Presentee Pour L'

Obtention Du

Doctorat En

Medecine Diplôme D'etat Papassin

Jérémie These

Soutenue Publiquement

A La

Faculte De Medecine De Grenoble

Président Du

Membres M Le Professeur

Mikael Mazighi

Tae-Hee Cho

M Le Docteur

Olivier Detante

Alexandre Krainik
email: alexandre.krainik@univ-grenoble-alpes.fr

Jérémie Papassin

Olivier Heck

Naïla Boudiaf Cd

Eric Condamine

Isabelle Favre

Sébastien Marcel

Kamel Boubagra

Katia Garambois

Florence Tahon

Johan Pietras

Altération de la vasoréactivité cérébrale en IRMf hypercapnique chez les patients présentant une sténose artérielle intracrânienne symptomatique d'origine athéromateuse à haut risque de récidive. THESE

Keywords: brain, stroke, intracranial arterial stenosis, DSC perfusion, BOLD fMRI, hypercapnia, cerebrovascular reserve

REMERCIEMENTS Aux membres du jury,

Au Professeur Mikael Mazighi, chercheur hors pair et neurologue interventionnel. Vous m'avez fait l'honneur de quitter la capitale pour venir présider ce jury.

Au Professeur Tae-Hee Cho, neurologue et excellent pédagogue. Je tenais absolument à ce que vous fassiez parti de ce jury pour apporter votre expertise à ce travail. Vos présentations en congrès ou en cours de DES sont toujours claires et pertinentes.

Au Docteur Olivier Detante, neurologue, show-man et chercheur passionné. Merci pour tes enseignements neurologiques et extra-neurologiques, tu as su me transmettre ton intérêt pour la science ainsi que ton dynamisme.

Au Professeur Alexandre Krainik, neuroradiologue et chercheur polyglotte. Toujours le mot pour rire. Merci pour la confiance que tu m'as accordé pour ce projet. Tu as su à la fois me laisser indépendant et être présent lorsqu'il le fallait.

Aux collègues et amis,

A Olivier Casez, ancienne star des terrains de foot, maintenant amateur de vin et d'arabica. Tu aurais fait aussi un excellent directeur de thèse. A tes côtés, j'ai appris à être médecin et (presque) neurologue, depuis le début de l'externat.

A Mathieu Vaillant. Les personnes qui t'ont élu neurologue le plus gentil du monde n'ont sûrement jamais couru ou monter à ski de rando avec toi, la cadence est insoutenable. Merci pour tes conseils et ta bienveillance.

A Gérard Besson. Homme érudit et musicien acharné vous avez façonné une véritable légende. J'ai hâte d'être CCA chez vous et d'apprendre à écrire mon prénom en hiéroglyphe.

A Katia Garambois. Je scrute maintenant avec attention le moindre ostium vertébral.

A Isabelle Favre « la dominatrice », assistante méticuleuse et avisée, tu aurais dû lire nos courriers d'hospitalisation jusqu'au bout… A Anne So, archétype de la femme du XXIème, capable de tout faire en même temps et très bien, à mes yeux (et à ceux de bon nombre d'hommes), c'est une chose incroyable.

A l'équipe médicale de neurologie A, merci de votre soutien pendant ces semestres au pays des stimulés et des implantés.

A l'équipe médicale de psychiatrie. Stage très enrichissant alors que je venais à reculons. J'ai appris les rudiments de la psychopathologie en abandonnant ma blouse de « somaticien » et mes objets contraphobiques (marteau réflexe et sthéto).

A l'équipe 5 du GIN dirigée par Emmanuel Barbier. Merci pour l'accueil que vous m'avez réservé dans le monde parallèle de la recherche. Pensées particulières à Claire, Nora et Ligia.

A Monsieur Tarel, neurologue passionné et homme juste, vous êtes un exemple pour moi. Merci pour les leçons du soir, vos expressions Shadoks et vos répliques à la Audiard.

A Marie Barre, une neurologue toujours classe en chaussures à paillettes. Jamais de fashion faux pas, Cristina Cordula serait fière de toi.

A Julien Gere. Merci à toi je sais dorénavant ce qu'est un waketeu.

A Nicolas Miret. Ton sens clinique aiguisé et ton bronzage de ski de rando m'ont toujours énervé (ceux sont plus des aveux que des remerciements, désolé…).

A toute les équipes paramédicales et secrétaires, merci pour votre attention et soutien tout au long de ces années. On s'est bien marré !! Aux co-internes et amis, Dans l'ordre d'apparition, Anne cath' ou Bernard pour les intimes, tu as donné le ton et le rythme (au pas de course) à cet internat ! Marine alias mariiiinnnnneeee a ensuite apporté sa douceur et son sourire. Alors que le bon Moumoun faisait semblant d'être un clinicien, mais tu ne trompes personne, on s'est que tu bluffes Martonni. Sérieusement, merci mec pour les bons et mauvais moments qu'on a passé ensemble. Formation par la suite du duo de choc avec Pauline, une co-interne brillante, esthète et championne toutes catégories confondues du radio-potin, j'ai hâte de reformer la team. Descente d'un étage et changement de pays, on se retrouve avec Emma (pulcino de la Basilicata) sous l'oeil attentif de Raul, à parler rigidité, voyages et fromages. Puis transfert chez l'ennemi voisin. Pendant que Bibi le bo goss, venu à Grenoble pour faire ses preuves en mouvement (pour finalement faire plomberie à Dijon), l'ami Seb assurait l'intendance… Qui aurait parié qu'avec ce zigoto chevelu nous allions trouver un remède miracle pour tous les zinzins, notre classique valiumtercian. La Ponce quant à elle affinait sa technique pour repousser les avances de nombreux prétendants et la Maze élaborait un sujet d'étude sur les trans-genres (bref des psychiatres, des vraies). Pour continuer sur le rythme effréné de la psychiatrie, rien de mieux qu'une année recherche. C'est avec Ligia (Lig' Lig') que j'apprenais à dompter les rongeurs. A l'écart du tumulte grenoblois, la bande de joyeux lurons composée d'Aurèle le mélenchoniste, Juju la présidente, la grosse Margo, Hélène IPA, Elo-psy et Louise le fou du volant collectionnaient les histoires de dingues !! Tout ça pour qu'au final, on décide de me faire redoubler… Heureusement, Catalina et Hugo bite de fer tiennent la boutique pendant que je finalise ce manuscrit. Pensées à tous les autres petits copains : Clem la pile électrique, Col-Col, le bon Gab', Marie la rêveuse, Nasty l'autobus, Anne la cycliste, Gio le plus grand neurologue, Rig', Thomas (je te prends quand tu veux au squash gros), la bonne Hélène, Guillaume et son baobab, Salma, Loïc le babyfooteux et Lucie (et son absence de second degré). Merci d'avoir été là, l'histoire aurait été moins drôle sans vous !

Aux copains,

Aux pedz', Badar, Vinc', Bilou, Malik et Valer, au plaisir de se matter une énième fois le pari et les 3 frères, ou de se retrouver pour un petit resto chinois à volonté et aux copines des bancs de l'école, Sophie, Mytien, Sandar' et Aurore. Amies de toujours et pour toujours.

Aux colocs de l'île verte. La bière, les nouilles chinoises, les cloisons en polystyrène et Fifa n'auront pas eu raison de nous. Alex&Aude vous êtes toujours prêts à m'accueillir sur Paris pour un F.I.E.A.L.D. ou un concert mais pour ce qui est de la grimpe… on a parlera à Peter. Ciol&Poupette, même en déménageant on arrive à être voisins, c'est con mais c'est très sympa. Merci Amel' pour ce que t'as fait pour la Grande et la Petite Jojo, et merci Gros pour la relecture de la thèse, je pense que tu seras la seule personne, peut être avec les membres du jury, à avoir lu ce papier.

Aux colocs de SMH. Nico l'OEdipe et Flo le poulpe, merci votre reprise de Toujours pas d'amour de Priscilla et vos fouines empaillées. Moumoun t'as bien essayé de incruster dans cette magnifique maison, on s'est que la moquette aux murs ça donne du cachet ! A la fine équipe, Ludo, Astrid, Yohan, Marjo', Flo & Flo, Martin, Jess, Nico, Krousti-Bat' et à tous les potes de promo, Marie Peg', la brune, Rom' et ses crocodiles, Z, Sof', Jean Luc, Manon, Jano, Simon. Je ne sais toujours pas pourquoi j'ai choisi neuro, à vous voir le cerveau n'est clairement pas un organe essentiel.

Pensée spéciale à Ludobite et la grosse Dièg', vous formez une excellente base arrière et de très bons con-pagnons de révision. « On s'est pas comment ça va finir, mais au moins on aura bien rigolé » A la bande de mecs (et meufs) sympas, Reda et Isle 187, La truite et MauMaud la Milf, Le nain et Bébéééee, Max et Alizée les petites personnes, Mat' Taïchi et Popo, Fred le romantique & Eva la teutonne. Vous êtes de grands malades ! Unis dès la P1 puis dispersés aux 4 coins de l'Europe et de la Savoie, nos retrouvailles donnent toujours mal au crâne.

A ma famille,

A Poup' et Mum, je ne serais pas là sans vous mais surtout je n'aurai jamais été celui que je suis sans votre soutien et votre amour. Je vous dois tout.

A ma tante Vivi, tu es la personne la plus drôle et aimante que je connaisse. Je te considère comme ma deuxième maman. Aux frérots, Raph' et Small T, mes complices. A courir derrière un ballon ou à de se mettre sur la gueule, je n'ai que de bons souvenirs avec vous.

A mes tantes, oncles, cousins et cousines et à tous les moments partagés ensemble. D'avoir une si belle famille est, à mes yeux, la plus grande des richesses.

A mes grands-parents, qui doivent sûrement me regarder d'où ils sont. Je pense souvent à vous, j'espère vous rendre fier.

A belle famille, qui me traîne à ski en haut de la Saulire ou dans les arcos. C'est toujours un plaisir de partager votre table! Vous faites beaucoup pour nous. Merci.

A Philippine.

Ravissante, pétillante, candide, tu es plus que ma moitié, je n'irai pas bien loin sans toi. Même s'il nous a fallu plus de 7 ans pour se rencontrer, j'espère ne plus perdre un seul instant et passer le restant de mes jours à tes côtés. Je t'aime ma belle.

A Agathe, MA fille. Introduction: Despite intensive medical management, intracranial atherosclerotic stenosis (IAS) remains at risk of recurrent ischemic events. Impaired cerebrovascular reserve is suggested to explain hemodynamic stroke. Cerebrovascular reactivity assessed by hypercapnic challenge using BOLD functional MRI (CVR BOLD fMRI) has been proposed to estimate cerebrovascular reserve and to identify patients at higher risk. To discuss patients' selection for additional therapy such as intracranial angioplasty and stenting, we studied the relationships between baseline characteristics of patients with unilateral symptomatic IAS, recurrence of ischemic events, and CVR BOLD fMRI.

LIST OF ABBREVIATIONS

Subjects and methods:

Nineteen patients with symptomatic unilateral IAS of middle cerebral artery (MCA) or internal carotid artery were selected. We calculated statistical relationships between individual clinical and biological baseline characteristics, recurrent ischemic events, basal perfusion estimated by dynamic susceptibility contrast MRI, and CVR BOLD fMRI measured in MCA territories (CVR MCA ), and reported using laterality indices (LI).

Results: Eight patients (42%) had an abnormal LI CVR MCA (|LI| CVR MCA ≥ 0.08). During a mean follow-up of 3.6 years, recurrent ischemic events occurred within the first year. They were more frequent in impaired CVR MCA group (n=6/8) than in normal CVR MCA group (n=1/11), with different survival curves (log rank, p=0.003). Baseline characteristics were similar in both groups.

Conclusion:

Impaired CVR assessed by BOLD hypercapnic fMRI is associated with increased risk of stroke in patients with symptomatic IAS. CVR mapping should be proposed to select high-risk patients in order to discuss additional treatment.

INTRODUCTION:

Intracranial atherosclerotic stenosis management

Intracranial atherosclerotic stenoses (IAS) account for approximately 10% of cerebrovascular ischemic strokes, and up to 50% in Asian populations [START_REF] Sacco | Race-ethnicity and determinants of intracranial atherosclerotic cerebral infarction. The Northern Manhattan Stroke Study[END_REF][START_REF] White | Ischemic stroke subtype incidence among whites, blacks, and Hispanics: the Northern Manhattan Study[END_REF][START_REF] Wong | Global burden of intracranial atherosclerosis[END_REF] . IAS are associated with high rates of recurrent ischemic event and cerebrovascular mortality when compared with other stroke subtypes [START_REF] Chimowitz | Comparison of warfarin and aspirin for symptomatic intracranial arterial stenosis[END_REF][START_REF] Holmstedt | Atherosclerotic intracranial arterial stenosis: risk factors, diagnosis, and treatment[END_REF] . The recurrence rate of ischemic events in the territory of the stenotic artery remains high [START_REF] Mazighi | Prospective study of symptomatic atherothrombotic intracranial stenoses: the GESICA study[END_REF][START_REF] Weber | Symptomatic Intracranial Atherosclerotic Stenoses: Prevalence and Prognosis in Patients with Acute Cerebral Ischemia[END_REF] , with a major risk of subsequent disabling stroke 8 , despite optimal medical treatment.

Large randomized trials demonstrated better outcomes with aggressive medical management compared to IAS recanalization using intracranial stenting [START_REF] Chimowitz | Stenting versus Aggressive Medical Therapy for Intracranial Arterial Stenosis[END_REF][START_REF] Zaidat | Effect of a balloon-expandable intracranial stent vs medical therapy on risk of stroke in patients with symptomatic intracranial stenosis: the VISSIT randomized clinical trial[END_REF] or surgical extracranial-intracranial bypass [START_REF] The | Failure of extracranial-intracranial arterial bypass to reduce the risk of ischemic stroke. Results of an international randomized trial. The EC/IC Bypass Study Group[END_REF][START_REF] Powers | Extracranial-intracranial bypass surgery for stroke prevention in hemodynamic cerebral ischemia: the Carotid Occlusion Surgery Study randomized trial[END_REF] to prevent recurrent stroke because of the high rate of procedural complications. Actually, a combination of antiplatelet therapies (aspirin 325mg per day plus clopidogrel 75mg per day for 90 days) is recommended with an intensive medical management of risk factors: high blood pressure, elevated low-density lipoprotein cholesterol (LDLc) levels, diabetes, smoking, overweight, and insufficient exercise [START_REF] Hoak | Management of Symptomatic Intracranial Stenosis[END_REF] . When life style adaptation is insufficient, antihypertensive drug and statin should be used to obtain a systolic blood pressure below 140 mmHg and LDLc level below 0.7g/l, respectively.

Vitamin K antagonists were associated with higher rates of adverse events and without benefit over aspirin [START_REF] Chimowitz | Comparison of warfarin and aspirin for symptomatic intracranial arterial stenosis[END_REF] . No clinical benefit was demonstrated for direct oral anticoagulant (direct IIa and Xa factor inhibitors) or other anti-platelet agents such as cilostazole or dipyridamole.

Despite optimal medical management, IAS remains associated with a recurrence rate of stroke events at 2 years of 15-25% [START_REF] Chimowitz | Comparison of warfarin and aspirin for symptomatic intracranial arterial stenosis[END_REF][START_REF] Chimowitz | Stenting versus Aggressive Medical Therapy for Intracranial Arterial Stenosis[END_REF] . The identification of risk factors of stroke recurrence among IAS patients under aggressive medical management would be helpful to consider alternative therapy [START_REF] Attyé | Normalization of cerebral vasoreactivity using BOLD MRI after intravascular stenting[END_REF][START_REF] Mandell | Quantitative Measurement of Cerebrovascular Reactivity by Blood Oxygen Level-Dependent MR Imaging in Patients with Intracranial Stenosis: Preoperative Cerebrovascular Reactivity Predicts the Effect of Extracranial-Intracranial Bypass Surgery[END_REF] . Indeed, old infarct in the territory of the stenosis, new stroke presentation, and absence of statin use at enrollment were independently associated with high recurrence rates of stroke events in the medical group in the SAMMPRIS trial [START_REF] Waters | Factors Associated With Recurrent Ischemic Stroke in the Medical Group of the SAMMPRIS Trial[END_REF] .

Additionally, impaired cerebrovascular reserve was suggested as a risk factor of stroke recurrence [START_REF] Gupta | Cerebrovascular reserve and stroke risk in patients with carotid stenosis or occlusion: a systematic review and meta-analysis[END_REF] .

Cerebrovascular functions

The cerebral vasomotricity leads to active changes of vessels resistance, through dilation and contraction, in order to adjust cerebral blood flow (CBF) in response to variations of neural activity (neurovascular coupling), to cerebral perfusion pressure (autoregulation), and to circulating gases and metabolites (vasoreactivity).

The neurovascular coupling adapts the cerebral blood flow to local neuronal activity providing oxygen, glucose and adenosine triphosphate to neurons and glia, and removing heat and catabolites [START_REF] Krainik | Functional imaging of cerebral perfusion[END_REF] .

The cerebral autoregulation refers to the ability of vasculature to maintain CBF constant, despite changes of perfusion pressure, to prevent ischemia-related brain damage.

Combination of myogenic, humoral and neurogenic feedback mechanisms are implicated in the regulation of adequate CBF maintaining constant distal perfusion pressure in brain capillaries during large arterial pressure variations [START_REF] Mchedlishvili | Physiological mechanisms controlling cerebral blood flow[END_REF][START_REF] Powers | Cerebral hemodynamics in ischemic cerebrovascular disease[END_REF] .

The cerebrovascular reactivity (CVR) modulates CBF in response to changes of circulating stimulus. Circulating gases such CO 2 and O 2 elicit vascular dilation and contraction, respectively, to maintain brain oxygenation.

Magnitude of the cerebrovascular properties is modulated by physiological changes (e.g. age, sex, hypoxia, arterial pressure, basal perfusion…), brain diseases (e.g. Alzheimer's disease; stroke,…), and structural vascular damage such as atherosclerosis (chronic arterial hypertension, diabetes,…) [START_REF] Krainik | Functional imaging of cerebral perfusion[END_REF][START_REF] Krainik | Regional impairment of cerebrovascular reactivity and BOLD signal in adults after stroke[END_REF] .

CVR assessment

When perfusion pressure decreases downstream the IAS, autoregulation may maintain CBF by vasodilation and cerebral blood volume increase. This additional dilation, known as cerebrovascular reserve, might be insufficient to compensate further perfusion pressure decrease. When cerebrovascular reserve is exhausted, patients are at risk of low grade ischemia and recurrent hemodynamic events [START_REF] Conklin | Mapping white matter diffusion and cerebrovascular reactivity in carotid occlusive disease[END_REF][START_REF] Bouvier | Reduced CMRO₂ and cerebrovascular reserve in patients with severe intracranial arterial stenosis: a combined multiparametric qBOLD oxygenation and BOLD fMRI study[END_REF] . Thus, the estimation of the cerebrovascular reserve using perfusion measures before and after vasodilatory stimulus has been proposed to identify patients at risk of ischemia [START_REF] Gupta | Cerebrovascular reserve and stroke risk in patients with carotid stenosis or occlusion: a systematic review and meta-analysis[END_REF][START_REF] Smeeing | Arterial Spin Labeling and Blood Oxygen Level-Dependent MRI Cerebrovascular Reactivity in Cerebrovascular Disease: A Systematic Review and Meta-Analysis[END_REF] .

While Positron Emission Tomography (PET) remains the "gold standard" technique [START_REF] Herold | Assessment of cerebral haemodynamic reserve: correlation between PET parameters and CO2 reactivity measured by the intravenous 133 xenon injection technique[END_REF] , noninvasive alternative methods have been advocated, such as transcranial Doppler sonography (TDS) [START_REF] Chen | Impaired dynamic cerebral autoregulation and cerebrovascular reactivity in middle cerebral artery stenosis[END_REF] , xenon-enhanced computed tomography [START_REF] Pindzola | Cerebrovascular Reserve in Patients With Carotid Occlusive Disease Assessed by Stable Xenon-Enhanced CT Cerebral Blood Flow and Transcranial Doppler[END_REF] , single-photon emission computed tomography (SPECT) [START_REF] Ogasawara | Cerebrovascular Reactivity to Acetazolamide and Outcome in Patients With Symptomatic Internal Carotid or Middle Cerebral Artery Occlusion[END_REF] , and more recently by functional magnetic resonance imaging (fMRI) using blood oxygenation level dependent (BOLD) contrast or arterial spin labelling (ASL) [START_REF] Smeeing | Arterial Spin Labeling and Blood Oxygen Level-Dependent MRI Cerebrovascular Reactivity in Cerebrovascular Disease: A Systematic Review and Meta-Analysis[END_REF] .

Most common vasodilatory stimuli are acetazolamide and CO 2 17,18 .

Among these techniques, BOLD CVR fMRI is an accessible, non-invasive, and reproducible whole brain imaging method [START_REF] Donahue | Routine Clinical Evaluation of Cerebrovascular Reserve Capacity Using Carbogen in Patients With Intracranial Stenosis[END_REF][START_REF] Spano | CO2 blood oxygen level-dependent MR mapping of cerebrovascular reserve in a clinical population: safety, tolerability, and technical feasibility[END_REF] . Among vasoactive stimuli, CO 2 challenge is safer when compared to hypotensive provocation. Intravenous acetazolamide administration is exposed to side effects, contraindications, and large inter-subject variability [START_REF] Fierstra | Measuring cerebrovascular reactivity: what stimulus to use?[END_REF] . Thus, well tolerated CO 2 inhalation with immediate and transient vasodilation is now advocated to be the most suitable stimulus [START_REF] Donahue | Routine Clinical Evaluation of Cerebrovascular Reserve Capacity Using Carbogen in Patients With Intracranial Stenosis[END_REF][START_REF] Spano | CO2 blood oxygen level-dependent MR mapping of cerebrovascular reserve in a clinical population: safety, tolerability, and technical feasibility[END_REF][START_REF] Fierstra | Measuring cerebrovascular reactivity: what stimulus to use?[END_REF] .

Objectives

Our objective was to investigate the relationships between clinical and biological characteristics of patients with unilateral symptomatic IAS, recurrence of ischemic events, basal perfusion parameters, and individual CVR mapping using BOLD hypercapnic fMRI. The study allowed to estimate: 1°) CVR and basal perfusion characteristics among patients with recurrent ischemic event, and 2°) occurrence of recurrent ischemic event in patients with CVR impairment.

SUBJECTS AND METHODS

Study participants

We conducted an observational study on adult patients referred at the University Hospital

Clinical data collection and follow-up

Qualifying ischemic event-related data was obtained from medical records and included stroke risk factors, medical history, National Institutes of Health Stroke Scale (NIHSS; 0 to 42, higher score indicating greater severity) at hospital admission, modified Rankin Scale (mRS; 0: no symptom to 6: death) at discharge, serum creatinine, glycosylated haemoglobin and lipid testing. Clinical follow-up period ranged from qualifying event until death, loss of follow-up or study end. All patients were seen yearly or more frequently if needed.

Recurrent stroke or TIA, adverse events and assessment of the patient's functional abilities and mobility using the mRS were conducted by a neurologist (JP, IF, KG, SM, OD) during visits or by telephone interview. Any stroke or TIA in the territory of the qualifying artery was considered to be a recurrent ischemic event. Ischemic events out of the territory of the qualifying artery or death were also analyzed.

MRI Protocol

All participants were scanned using a 3T ACHIEVA TX MR scanner (Philips Healthcare®, the Netherlands) at University Hospital Grenoble Alps, using a whole-body RF transmit and 8 channels head receive coils. All participants had anatomical, basal perfusion, and BOLD CVR studies.

Anatomical study

Anatomical study consisted in a 3D gradient recalled echo (GRE) T1-weighted image (WI) (160 contiguous slices, slice thickness=1mm, TR/TE/α: 9.9/4.6ms/8°, 256x256 matrix, field of view (FOV) of 256x160 mm for 4.5 min acquisition time).

Basal perfusion study

Perfusion-WI was performed using dynamic T2

Images processing and analyses

Data analysis was performed with Amigo, an in-house post-processing suite written in Python 3.6 using Matlab (MathWorks, Inc., Natick, MA, USA) and SPM12 (SPM, Wellcome Department of Imaging Neuroscience).

Anatomical data

White and gray matters (GM) were segmented through the 3D GRE T1 sequence using the standard space tissue probability maps from SPM12. GM maps were spatially normalized to the Montreal Neurologic Institute (MNI) T1-weighted template and resampled at 2x2x2mm resolution. GM maps were further smoothed with a 6-mm Gaussian Kernel for Regions of Interest (ROI) analyses.

Basal perfusion data

Basal perfusion images preprocessing consisted in coregistration, normalization, resampling onto anatomical images, and spatial smoothing with a 6-mm Gaussian Kernel. The arterial input function (AIF) was estimated by averaging 5 voxels from all slices of the perfusion scan during the dynamics. These 5 voxels were automatically detected by optimizing a function with a signal evolution characterized by the higher peak height, a faster dropout, concomitant to a smaller full-width-half-maximum and bolus arrival time (brain-feeding artery detection). Mean Transit Time (MTT) maps were then calculated pixel-wise with a deconvolution approach based on a singular value decomposition using a tracer arrival timing insensitive method and an automatic regularization of oscillations [START_REF] Wu | Tracer arrival timing-insensitive technique for estimating flow in MR perfusion-weighted imaging using singular value decomposition with a block-circulant deconvolution matrix[END_REF] . The relative Cerebral Blood Volume (CBV) was estimated from the area under the curve of the voxel concentration. To obtain quantitative maps, the mean brain CBV was normalized to 5%. The MTT maps were estimated from the area under the curve and from the time to maximum of the deconvolved function respectively. CBF was calculated as the ratio CBV/MTT from the central volume theorem. The excluded voxels from the computation were averaged with the nearby voxels.

CVR data

BOLD CVR images preprocessing consisted in coregistration, normalization, resampling onto anatomical images, and spatial smoothing with a 6-mm Gaussian Kernel. Statistical analysis was conducted using a general linear model and the individual PetCO 2 in mmHg as a physiological regressor. CVR maps were expressed as percent change of BOLD signal per mmHg change of PetCO 2 (%BOLD/ PetCO 2 mmHg). Illustrative case is shown in Figure 1. Calculation of a LI was also used for all basal perfusion parameters (CBF, CBV, or MTT) and in other ROI.

Statistical analyses

Analyses were performed using the SPSS 20.0. Non-parametric statistics were conducted because of small sample sizes. Intergroup comparisons were conducted using Mann-Whitney U tests. Relationship between CVR MCA status and recurrent ipsilateral ischemic event was determined using Kaplan-Meier analysis with log rank comparison. Correlations between basal perfusion parameters and CVR MCA were assessed by Spearman's ρ correlation coefficient. All tests were two-tailed and a p value < 0.05 was considered statistically significant.

RESULTS:

Twenty-one patients satisfied inclusion criteria. No adverse reaction to the Gadolinium-dota administration and to hypercapnic stimulus was reported. Two patients were excluded because of incomplete protocol realization secondary to discomfort due to the face mask within the head coil (n=1) and inappropriate hypercapnic stimulus (n=1), leaving 19 patients for further analyses. Finally, 13 men and 6 women were included, with a mean age of 61.0 years (SD ±12.5). Clinical and biological baseline characteristics are presented in During follow-up (mean±SD=3.57±1.43 years), we identified 2 groups: 12 patients had a single ischemic qualifying event (SINGLE), and 7 patients experienced a recurrent ipsilateral ischemic event (RECURRENT), of which 3 strokes and 4 TIA (Table 2). Overall annual risk of recurrent ipsilateral ischemic event was 18.4% per year. An ischemic event out of the qualifying IAS territory occurred in 3 patients (2 in RECURRENT group and 1 in SINGLE group).

No intracranial hemorrhage was detected on follow-up. One death caused by acute pulmonary edema was reported at 3.5 years follow-up for a patient from SINGLE group.

Annual risk of recurrent combination of all ischemic events and death was 24.2% per year. 1.

N°

Comparisons between SINGLE and RECURRENT groups

When compared with SINGLE, RECURRENT patients were older (69.5±9.1. vs 56.1±11.8 p=0.04). There were no differences among other clinical and biological data (Table 3). Patients who experiment recurrent ipsilateral ischemic event are significantly older than SINGLE patients. Data are mean ± standard deviation. Abbreviations are defined in Table 1.

SINGLE

RECURRENT patients had higher |LI| CVR MCA (0.14±0.05 vs 0.05±0.03, p=0.001). There were no differences among |LI| CVR in other arterial territories. Subtle intergroup differences in basal perfusion parameters did not reach significance (Table 4). 4: Laterality indices between SINGLE and RECURRENT groups for each vascular ROI and each hemodynamic parameter (cerebrovascular reactivity, basal perfusion parameters). The |LI| CVR MCA is significantly increased in patients who experiment recurrent ipsilateral ischemic event, other hemodynamic parameters differ between these two groups. Data are mean ± standard deviation. |LI|=absolute value of laterality index, CVR=cerebrovascular reactivity, CBF=cerebral blood flow, CBV=cerebral blood volume, MTT=mean time transit, ACA=anterior cerebral artery territories, PCA=posterior cerebral artery territories, other abbreviations are defined in Table 1.

SINGLE

Illustrative cases are shown in Figure 3.

Comparisons between IMPAIRED and NORMAL CVR MCA groups

Among all patients, 11 patients had NORMAL CVR MCA , and 8 had IMPAIRED CVR MCA . There were no intergroup differences among clinical and biological baseline data (Table 5). 1.

NORMAL CVR

The occurrence of recurrent ipsilateral ischemic event in IMPAIRED CVR MCA (n=6/8) was more frequent than in NORMAL CVR MCA group (n=1/11) with different survival curves (p=0.003) (Figure 4). The annual risk of recurrent ipsilateral ischemic event was higher in IMPAIRED CVR MCA group compared to NORMAL CVR MCA group (39.1%/year vs 3.4%/year, p=0.012). There were neither differences among |LI| CVR in other arterial territories nor in other basal perfusion parameters (Table 6). 6: Laterality indices between NORMAL and IMPAIRED CVR MCA groups for each vascular ROI and each hemodynamic parameter (cerebrovascular reactivity, basal perfusion parameters). Except |LI| CVR MCA , no other hemodynamic parameters differ significantly between these two groups. Data are mean ± standard deviation. Abbreviations are defined in Table 4.

NORMAL CVR

CVR MCA and basal perfusion parameters correlations

We found a positive correlations between LI CVR MCA and LI CBF MCA (ρ=0.89, p=0.007 vs ρ=0.59, p=0.043) for RECURRENT and SINGLE patients, respectively (Figure 5). A significant negative correlation was found between LI CVR MCA and LI MTT MCA in RECURRENT group (ρ=-0.86, p=0.014) but not significant in SINGLE group (ρ=-0.47, p=0.12). For both groups, LI CVR MCA was not significantly correlated with LI CBV MCA .

DISCUSSION:

In patients with symptomatic intracranial atherosclerotic stenosis, recurrent ischemic events occur despite optimal medical therapy. Additional treatments such as endovascular angioplasty and stenting are still not validated. Indeed, large trials failed to demonstrate significant clinical benefits when compared to higher risks of mordibity and mortality. To further address additional therapy, the estimation of cerebrovascular reserve may help to better identify patients at higher risk of stroke recurrence. In our observational study, we showed that 1°) patients with recurrent ischemic events have an impaired CVR downstream the IAS, using BOLD fMRI with hypercapnic challenge; 2°) patients with abnormal CVR defined by a laterality index ≥0.08 are at higher risk of recurrent ischemic events. These results emphasized the potential role of CVR fMRI to select patients for additional treatment.

In our study, the global rate of recurrence of ischemic event was 37%, similar to 38% observed in GESICA study [START_REF] Mazighi | Prospective study of symptomatic atherothrombotic intracranial stenoses: the GESICA study[END_REF] . The annual rate of stroke downstream the qualifying IAS was also close to 18% reported in the severe IAS subgroup of WASID trial, but higher than 12% in the SAMMPRIS trial [START_REF] Chimowitz | Comparison of warfarin and aspirin for symptomatic intracranial arterial stenosis[END_REF][START_REF] Chimowitz | Stenting versus Aggressive Medical Therapy for Intracranial Arterial Stenosis[END_REF] . We used identical restrictive inclusion and exclusion criteria. This led to analyze a much smaller population in our monocentric study. However, clinical baseline characteristics were similar. In SAMMPRIS, a more intensive control of cardiovascular risk factors, based on a tight clinical and biological follow-up and a lifestyle modification program may explain this difference [START_REF] Chimowitz | Stenting versus Aggressive Medical Therapy for Intracranial Arterial Stenosis[END_REF] .

We identified a high-risk subgroup, i.e. patients with IMPAIRED CVR MCA had a rate of ipsilateral recurrent ischemic event of 39%/year when compared to 3%/year in NORMAL CVR MCA patients. The 13x higher rate in patients with CVR impairment advocates for a tight relationship. Reduced CVR has been identified as a strong and independent predictor on stroke recurrence in steno-occlusive diseases, using multivariate analysis among other variables (cardiovascular risk factors, degree of stenosis) [START_REF] Ogasawara | Cerebrovascular Reactivity to Acetazolamide and Outcome in Patients With Symptomatic Internal Carotid or Middle Cerebral Artery Occlusion[END_REF][START_REF] Markus | Severely impaired cerebrovascular reactivity predicts stroke and TIA risk in patients with carotid artery stenosis and occlusion[END_REF][START_REF] Reinhard | Cerebrovascular reactivity predicts stroke in high-grade carotid artery disease[END_REF] . Most of these CVR studies used TDS with several advantages, such as high temporal resolution, arterial velocity quantification, non-invasiveness, cost, and availability, and limitations such as insonation window access, interoperator variability, absence of parenchymal imaging. Functional brain imaging techniques using SPECT, and MRI have been proposed to explore whole brain CVR [START_REF] Gupta | Cerebrovascular reserve and stroke risk in patients with carotid stenosis or occlusion: a systematic review and meta-analysis[END_REF][START_REF] Krainik | Functional imaging of cerebral perfusion[END_REF] . However, fMRI studies on steno-occlusive diseases were heterogeneous with extracranial and/or stenosis or occlusion, and with different etiologies such as atheromatous or moya-moya [START_REF] Mandell | Quantitative Measurement of Cerebrovascular Reactivity by Blood Oxygen Level-Dependent MR Imaging in Patients with Intracranial Stenosis: Preoperative Cerebrovascular Reactivity Predicts the Effect of Extracranial-Intracranial Bypass Surgery[END_REF][START_REF] Smeeing | Arterial Spin Labeling and Blood Oxygen Level-Dependent MRI Cerebrovascular Reactivity in Cerebrovascular Disease: A Systematic Review and Meta-Analysis[END_REF][START_REF] Donahue | Routine Clinical Evaluation of Cerebrovascular Reserve Capacity Using Carbogen in Patients With Intracranial Stenosis[END_REF][START_REF] Spano | CO2 blood oxygen level-dependent MR mapping of cerebrovascular reserve in a clinical population: safety, tolerability, and technical feasibility[END_REF][START_REF] Goode | Impaired Cerebrovascular Reactivity Predicts Recurrent Symptoms in Patients with Carotid Artery Occlusion: A Hypercapnia BOLD fMRI Study[END_REF][START_REF] Haller | Reduced cerebrovascular reserve at CO2 BOLD MR imaging is associated with increased risk of periinterventional ischemic lesions during carotid endarterectomy or stent placement: preliminary results[END_REF] . Our study is the first one to evaluate CVR using fMRI in a homogeneous group of patients with symptomatic atherosclerotic stenosis of a major intracranial artery, like in large randomized trials [START_REF] Chimowitz | Comparison of warfarin and aspirin for symptomatic intracranial arterial stenosis[END_REF][START_REF] Chimowitz | Stenting versus Aggressive Medical Therapy for Intracranial Arterial Stenosis[END_REF] .

BOLD fMRI with hypercapnic challenge has been shown as a safe and reliable brain imaging technique to estimate cerebrovascular reserve [START_REF] Donahue | Routine Clinical Evaluation of Cerebrovascular Reserve Capacity Using Carbogen in Patients With Intracranial Stenosis[END_REF][START_REF] Spano | CO2 blood oxygen level-dependent MR mapping of cerebrovascular reserve in a clinical population: safety, tolerability, and technical feasibility[END_REF] . However BOLD signal, which reveals changes in blood oxygenation, remains an unclear combination of variation in oxygenation consumption, CBF, CBV, and vasomotricity. Perfusion MRI techniques such as ASL were also proposed to monitor quantitative CBF changes to vasomotor stimuli [START_REF] Smeeing | Arterial Spin Labeling and Blood Oxygen Level-Dependent MRI Cerebrovascular Reactivity in Cerebrovascular Disease: A Systematic Review and Meta-Analysis[END_REF][START_REF] Villien | Changes in cerebral blood flow and vasoreactivity to CO2 measured by arterial spin labeling after 6days at 4350m[END_REF] . In our experience, CVR fMRI using ASL remains difficult to implement in clinical work-flow, mostly limited by a poor signal to noise ratio, a lower temporal resolution (8 sec between 2 pairs of tag-control images), a critical sensitivity to labeling temporal parameters with aging and arterial transit time asymmetry a fortiori downstream IAS, sophisticated postprocessing that requires parametric assumptions and signal corrections for "absolute" CBF quantification [START_REF] Vincent | Bayesian joint detection-estimation of cerebral vasoreactivity from ASL fMRI data[END_REF][START_REF] Villien | Per-subject characterization of bolus width in pulsed arterial spin labeling using bolus turbo sampling[END_REF] .

Because of the variability of basal perfusion and CVR, we chose to estimate these parameters independently, to calculate LI to minimize interindividual amplitude effects, and to test their relationships [START_REF] Bouvier | Reduced CMRO₂ and cerebrovascular reserve in patients with severe intracranial arterial stenosis: a combined multiparametric qBOLD oxygenation and BOLD fMRI study[END_REF] . Using classical LI, as defined for hemispheric lateralization for language, we previously shown that 95% of 100 healthy subjects, had CVR |LI|<0.08 [START_REF] Boudiaf | BOLD fMRI of cerebrovascular reactivity in the middle cerebral artery territory: A 100 volunteers' study[END_REF] . In the present study, all RECURRENT patients but one had a CVR |LI|≥0.08. Based on both of these results, IMPAIRED CVR MCA had a much higher risk of ischemic event, suggesting a reliable threshold to select patients at high risk in a future prospective study. However, the asymmetry characterization is less relevant and limits results interpretation in case of bilateral stenosis. Thus, absolute CVR quantification would be helpful to further address these limitations, although physiological and pathological confounds account for a large inter-individual variability [START_REF] Krainik | Functional imaging of cerebral perfusion[END_REF][START_REF] Smeeing | Arterial Spin Labeling and Blood Oxygen Level-Dependent MRI Cerebrovascular Reactivity in Cerebrovascular Disease: A Systematic Review and Meta-Analysis[END_REF][START_REF] Boudiaf | BOLD fMRI of cerebrovascular reactivity in the middle cerebral artery territory: A 100 volunteers' study[END_REF] .

In a previous study, basal CBF decrease and CVR impairment explained decreased parenchymal oxygenation, suggesting chronic low grade ischemia in patients with symptomatic IAS [START_REF] Bouvier | Reduced CMRO₂ and cerebrovascular reserve in patients with severe intracranial arterial stenosis: a combined multiparametric qBOLD oxygenation and BOLD fMRI study[END_REF] . Here, CBF and CVR asymmetry were correlated in both RECURRENT and SINGLE patients. The correlation coefficient was higher in the RECURRENT group. However the small groups' size did not allow to conduct appropriate statistical comparison. Despite these relationships, CVR asymmetry was the only significant parameter which differed across RECURRENT and SINGLE groups.

In fact, most recurrent ischemic events downstream IAS occurred during the first year after qualifying event, in line with large clinical trials [START_REF] Chimowitz | Comparison of warfarin and aspirin for symptomatic intracranial arterial stenosis[END_REF][START_REF] Chimowitz | Stenting versus Aggressive Medical Therapy for Intracranial Arterial Stenosis[END_REF] . This observation suggests time-dependent changes of the plaque under aggressive medical management, collateral supply development, and adaptive cerebrovascular reserve increase. Indeed, IAS are dynamic and degree of stenosis may progress or regress over time [START_REF] Akins | Natural history of stenosis from intracranial atherosclerosis by serial angiography[END_REF] . The risk of new stroke is attenuated after 1 year by the stabilization of vulnerable plaque, and development of collateral circulation [START_REF] Liebeskind | Collaterals dramatically alter stroke risk in intracranial atherosclerosis[END_REF] . Intensive medical management should therefore accelerate these different protective processes [START_REF] Sander | Improved Cerebral Vasoreactivity After Statin Administration in Healthy Adults[END_REF][START_REF] Sterzer | Pravastatin Improves Cerebral Vasomotor Reactivity in Patients With Subcortical Small-Vessel Disease[END_REF] . Beside structural changes of vascularization, functional changes of arterial supply may also occur. Several cases of spontaneous improvement of cerebrovascular reserve were reported using SPECT [START_REF] Hasegawa | Sequential change of hemodynamic reserve in patients with major cerebral artery occlusion or severe stenosis[END_REF] . However, temporal changes of cerebrovascular reserve remain to be documented in larger studies. A systematic CVR mapping and basal perfusion imaging follow-up would be interesting in order to test spatial agreement between CVR impairment and recurrent stroke, and to monitor natural evolution of CVR and basal perfusion.

Additionally to hemodynamic ischemic event related to CVR impairment, artery-to-artery embolism, in situ thrombo-occlusion, and occlusion of perforating arteries are other key pathophysiological mechanisms underlying cerebral ischemia in patients with IAS [START_REF] Van Den Wijngaard | Treatment and imaging of intracranial atherosclerotic stenosis: current perspectives and future directions[END_REF] . Dual antiplatelet therapy and restrictive medical management of cardiovascular factors decrease the risk of disability and death following recurrent stroke in and out the stenosis territory over extended follow-up [START_REF] Chimowitz | Stenting versus Aggressive Medical Therapy for Intracranial Arterial Stenosis[END_REF] . Indeed, stroke out the qualifying artery territory and cardiovascular death also occurred, as in large trials [START_REF] Chimowitz | Comparison of warfarin and aspirin for symptomatic intracranial arterial stenosis[END_REF][START_REF] Mazighi | Prospective study of symptomatic atherothrombotic intracranial stenoses: the GESICA study[END_REF][START_REF] Weber | Symptomatic Intracranial Atherosclerotic Stenoses: Prevalence and Prognosis in Patients with Acute Cerebral Ischemia[END_REF][8][START_REF] Chimowitz | Stenting versus Aggressive Medical Therapy for Intracranial Arterial Stenosis[END_REF] , in 4 patients out of 19, independently of CVR MCA status.

Given to our results, prevention of stroke recurrence within the first year remains the most critical therapeutic challenge after the acute stroke management. CVR fMRI would be useful to select high-risk patients and to may help to justify peri-procedural adverse events related to additional invasive treatment. We suggest that future therapeutic trials on endovascular techniques using stents [START_REF] Ding | Role of stenting for intracranial atherosclerosis in the post-SAMMPRIS era[END_REF] or angioplasty alone [START_REF] Dumont | Submaximal angioplasty for symptomatic intracranial atherosclerosis: a prospective Phase I study[END_REF] , should be first conducted on IAS patients with CVR impairment, only.

CONCLUSION:

Symptomatic intracranial atherosclerotic stenosis is associated with high rates of subsequent stroke and cerebrovascular mortality. Prevention of recurrent ischemic events remains challenging. Using noninvasive CVR BOLD fMRI, LI CVR MCA derived from asymmetric BOLD signal change, elicited by hypercapnic stimulus, shows that CVR impairment is observed in more than 40% of patients with unilateral symptomatic IAS. An increased |LI| CVR MCA is associated with a major risk of ipsilateral recurrent ischemic event. CVR MCA impairment is more frequent in patients with recurrent versus single event. CVR impairment significantly shortens event-free survival during the first year, despite optimal medical management. CVR status should be considered to identify among IAS patients those at a higher risk of recurrent ischemic event and to select those who may benefit from additional treatment, such as endovascular procedures.

ACA:

  anterior cerebral artery AIF: arterial input function ASL: arterial spin labelling BOLD: blood oxygenation level dependent CBF: cerebral blood flow CBV: cerebral blood volume CVR: cerebrovascular reactivity EPI: echo-planar imaging fMRI: functional magnetic resonance imaging FOV: field of view GM: gray matter GRE: gradient recalled echo IAS: intracranial atherosclerotic stenosis ICA: internal carotid artery LDLc: low-density lipoprotein cholesterol LI: laterality index MCA: middle cerebral artery MNI: Montreal Neurologic Institute mRS: modified Rankin scale MTT: Mean Transit Time NIHSS: National Institutes of Health Stroke Scale PCA: posterior cerebral artery PET: positron emission tomography PetCO 2 : end-tidal CO 2 pressure RECURRENT: recurrent ipsilateral ischemic event ROI: regions of interest SINGLE: single ischemic qualifying event SPECT: single-photon emission computed tomography TDS: transcranial Doppler sonography TIA: transient ischemic attack WI: weighted images ABSTRACT:

Figure 1 :

 1 Figure 1: FLAIR-T 2 weighted image (A), Time-Of-Flight weighted image (B), basal perfusion parameters and CVR maps in 68-year woman referred for symptomatic right MCA stenosis in red arrow, without ischemic recurrence (radiological convention).

Figure 2 :

 2 Figure 2: Individual regions of interest in major cerebral arteries territories.

Figure 3 :

 3 Figure 3: Basal perfusion parameters and CVR maps in patients referred for symptomatic right MCA severe stenosis (radiological convention). Upper row: 65-years man without ischemic recurrence (SINGLE group). Both basal perfusion (CBF, CBV, MTT) and CVR MCA were symmetrical: |LI| CBF MCA =0.00, |LI| CBV MCA =0.00, |LI| MTT MCA =0.01, |LI| CVR MCA =0.02 (NORMAL CVR MCA ). Lower row: 83-years woman with 2 recurrent transient ischemic attacks (RECURRENT group). Autoregulation with increased CBV failed to maintain CBF symmetrical. Additionally, CVR decreased downstream MCA stenosis: |LI| CBF MCA =0.18, |LI| CBV MCA =0.06, |LI| MTT MCA =0.22, |LI| CVR MCA = 0.19 (IMPAIRED CVR MCA ).

Figure 4 :

 4 Figure 4: Kaplan-Meier survival curves illustrating the relationship between CVR MCA and the occurrence of ipsilateral ischemic event. The vertical cross-lines indicates patient whose data were censored due to study end, death, or recurrent ischemic event.

Figure 5 :

 5 Figure 5: Positive correlations between LI CBF and LI CVR from middle cerebral artery territories (ρ=0.89, p=0.007 vs ρ=0.59, p=0.043) for RECURRENT and SINGLE patients with intracranial stenosis, respectively.

  This injection was flushed by a bolus of physiological saline (60mL). To obtain an accurate estimate of the baseline MR signal intensity S(0) prior to the arrival of contrast agent an injection delay of 10 seconds was applied. Eighty single-shot, gradient-echo, echo-planar images, were obtained in each of the slices during the 2'11 minute acquisition time.

	CVR study
	CVR imaging consisted in BOLD sensitive T2* WI GRE EPI acquisition (32 axial slices, slice
	thickness=4mm, TR/TE/α: 3000/35ms/90°, 64x64 matrix, FOV=256x256 mm, 240 dynamics)
	with a whole brain coverage. Hypercapnic challenge was conducted according to the
	*-WI GRE echo-planar imaging (EPI) (25
	contiguous slices, thickness=4mm, TR/TE/α: 1660/40ms/75°, 112x112 matrix,

FOV=224x184mm), tracking a bolus of 0.1mmol/kg of Gadolinium (Guerbet®, France), injected at a rate of 5mL/s with a MR compatible injector (MEDRAD®, USA). following block-designed paradigm [air(1′)-hypercapnia(2′)-air(1′)]×3, for a total duration of 12 minutes. Each participant was exposed alternatively to medical air and to a hypercapnic normoxic gas mixture (CO 2 (8%), O 2 (21%), and N 2 (71%) through a non-rebreathing face mask. Physiological parameters, including end-tidal CO 2 pressure (PetCO 2 ), arterial oxygen saturation, breath frequency and heart rate were monitored using a MR compatible device (Maglife, Schiller medical). This protocol induces an increase PetCO 2 about 10 mm Hg, recorded via nasal cannula.

Table 1

 1

	. IAS

Table 1 :

 1 Clinical and biological baseline characteristics. Data are mean ±standard deviation. IAS=intracranial atherosclerotic stenosis, TIA=transient ischemic attack, MCA=first segment of middle cerebral artery, ICA=internal carotid artery, NIHSS=National Institutes of Health Stroke Scale, mRS=modified Rankin Scale, [IQR]=interquartile range.

Table 2 :

 2 Summary details of RECURRENT patients. |LI|CVR MCA =absolute value of laterality index of cerebrovascular reactivity in middle cerebral artery territories, other abbreviations are defined in Table

		Age	Sex Qualifying	Location	|LI|	Days to	Details of
		(years)		event	of	CVR MCA	recurrent	recurrent
					stenosis		event	event
	1	80	F	Stroke	MCA	0.05	84	TIA
	2	63	F	Stroke	MCA	0.12	182	TIA
	3	63	M	Stroke	MCA	0.12	24	Stroke
	4	72	M	TIA	ICA	0.13	110	TIA
	5	64	M	Stroke	ICA	0.14	173	Stroke
	6	84	F	TIA	MCA	0.19	2	TIA
	7	62	M	Stroke	MCA	0.20	9	Stroke

Table 3 :

 3 Clinical and biological baseline characteristics of SINGLE and RECURRENT groups.

	group	RECURRENT	p value
	(n=12)	group (n=7)

Table 5 :

 5 Baseline characteristics of NORMAL and IMPAIRED CVR MCA groups. Clinical and biological data are similar between patients with and without CVR impairment downstream the intracranial stenosis. Data are mean ± standard deviation. CVR MCA =cerebrovascular reactivity on middle cerebral artery territories, other abbreviations are defined in Table

	MCA	IMPAIRED CVR MCA	p value
	group (n=11)	group (n=8)

Impaired cerebrovascular reactivity assessed by BOLD hypercapnic fMRI is associated with increased risk of stroke in patients with symptomatic intracranial atherosclerotic stenosis

Introduction: Despite intensive medical management, intracranial atherosclerotic stenosis (IAS) remains at risk of recurrent ischemic events. Impaired cerebrovascular reserve is suggested to explain hemodynamic stroke. Cerebrovascular reactivity assessed by hypercapnic challenge using BOLD functional MRI (CVR BOLD fMRI) has been proposed to estimate cerebrovascular reserve and to identify patients at higher risk. To discuss patients' selection for additional therapy such as intracranial angioplasty and stenting, we studied the relationships between baseline characteristics of patients with unilateral symptomatic IAS, recurrence of ischemic events, and CVR BOLD fMRI.

Subjects and methods:

Nineteen patients with symptomatic unilateral IAS of middle cerebral artery (MCA) or internal carotid artery were selected. We calculated statistical relationships between individual clinical and biological baseline characteristics, recurrent ischemic events, basal perfusion estimated by dynamic susceptibility contrast MRI, and CVR BOLD fMRI measured in MCA territories (CVR MCA ), and reported using laterality indices (LI).

Results

Conclusion:

Impaired CVR assessed by BOLD hypercapnic fMRI is associated with increased risk of stroke in patients with symptomatic IAS. CVR mapping should be proposed to select high-risk patients in order to discuss additional treatment.


Présentée Pour L'

Obtention Du

Doctorat En

Médecine Diplôme D'état Mademoiselle

MD Sandie Pestour

Président Du

Monsieur Le Professeur

Vincent Leroy

Bruno Bonaz Monsieur Le Professeur Stéphane

Nancey Monsieur Le Docteur

PhD Nicolas Mathieu
email: nmathieu@chu-grenoble.fr

Monsieur Le Docteur

S Nancey

PhD A L Charlois

B Bonaz

PhD G Boschetti

Influence de la localisation des maladies inflammatoires chroniques de l'intestin sur l'efficacité du Védolizumab : une étude multicentrique THÈSE

Keywords: Crohn's Disease, Ulcerative colitis, ileal location, colonic location, extensive colitis

À Monsieur le Professeur Vincent LEROY, Chef du service d'Hépato-gastro

ABBREVIATIONS

Colitis (UC), are characterized by a chronic and excessive inflammation located in the gastro-intestinal tract. In UC, lesions are localized exclusively in the rectum and colon whereas in CD, all parts of the digestive tract can be involved (ileocaecal location most frequently). IBD have a chronic evolution, with an alternation of remission periods and flares [START_REF] Baumgart | Crohn's disease[END_REF].

Owing to early life beginning, chronic evolution, and disabling digestive symptoms during flares, IBD induce a high morbidity rate leading to an impaired quality of life [2; 3]. Moreover, although the impact of IBD on global mortality is low, complications such as acute severe colitis, occlusion, perforation, infection, abscess, and malnutrition can occur and be life-threatening for the patient [START_REF] Peyrin-Biroulet | The natural history of adult Crohn's disease in population-based cohorts[END_REF].

The IBD incidence (CD, 12.7 per 100,000 person-years / UC, 24.3 per 100,000 person-years in Europe) and prevalence (CD, 322 per 100,000 / UC, 505 per 100,000 in Europe) are increasing worldwide, resulting in a heavy social and economic burden for healthcare systems. This is due firstly to possible disease complications (hospitalization, surgery) and secondly because of the use of strong, costly, and long-term therapies [5; 6]. Therefore, the management of available therapies is a real public health issue, in particular for moderate to severe disease forms. Current therapies include corticosteroids (CS), immunosuppressant drugs (azathioprine, mercaptopurine, methotrexate), and tumor necrosis factor (TNF) antagonists (infliximab/adalimumab/golimumab/certolizumab pegol). CS are effective when used to induce remission but not as a maintenance therapy.

Immunosuppressants are slow-acting drugs that are not able to induce remission.

TNF antagonists can induce and maintain remission but not in the long term for most (more than 50% of secondary loss of response at 1 year) [1; 4]. Current therapies have been reported to induce several systemic and potentially disabling adverse effects. That is why there is an increasing interest for emerging drugs with more selective mechanism of action, such as anti-migration therapies.

Vedolizumab (VDZ) is a fully humanized immunoglobin G 1 monoclonal antibody which specifically targets the  4  7 -integrin on activated leukocytes and inhibits its ability to bind with Mucosal Addressin Cell Adhesion Molecule (MadCAM-1) localized in the digestive endothelium. By blocking  4  7 -integrin, VDZ prevents translocation of leukocytes, especially gut-homing T lymphocytes, from the blood to inflamed intestinal tissue, and then selectively downregulates gut inflammation. Such a mechanism of action, restricted to the gastrointestinal tract, should not affect the whole systemic immune responses, allowing to reduce the risk of infection and to minimize adverse effects of systemic usual IBD immunosuppressive therapies. VDZ can induce and maintain remission both in CD and UC as demonstrated in 3 pivotal phase 3 clinical trials [START_REF] Feagan | GEMINI 1 Study Group. Vedolizumab as induction and maintenance therapy for Ulcerative Colitis[END_REF][START_REF] Sandborn | GEMINI 2 Study Group. Vedolizumab as induction and maintenance therapy for Crohn's disease[END_REF][START_REF] Sands | Effects of vedolizumab induction therapy for patients with Crohn's disease in whom tumor necrosis factor antagonist treatment failed[END_REF].

Identifying the predictive factors of therapeutic response is crucial since it allows choosing more personalized therapeutic strategies for each patient, in particular in terms of cost-effectiveness. Various factors associated with a pejorative response to VDZ in IBD patients have been identified, including smoking history, prior TNF antagonist therapy, active perineal disease for CD, elevated C-Reactive Protein (CRP) in UC, severe activity of IBD, and also trough levels of VDZ during the induction regimen [7; 8; 10-12]. Moreover, albumin serum level and body weight values have been reported to impact drug clearance [START_REF] Rosario | Population pharmacokinetics-pharmacodynamics of vedolizumab in patients with ulcerative colitis and Crohn's disease[END_REF].

In UC, extensive colitis (pancolitis) usually has a more pejorative prognosis, with a higher risk of colectomy, than distal location [START_REF] Al-Darmaki | Clinical Predictors of the Risk of Early Colectomy in Ulcerative Colitis: A Population-based Study[END_REF]. In CD, ileal and perineal locations are more severe than colonic locations, probably owing to the subsequent associated complications such as fistula and strictures which occur more frequently, whereas the colonic involvement exhibits a preferential association with the inflammatory phenotype of the disease [START_REF] Laharie | Predictors of response to infliximab in luminal Crohn's disease[END_REF]. Moreover, the authors of several cohort studies have also assessed colonic CD as predictor of better response to anti-TNF therapy [START_REF] Laharie | Predictors of response to infliximab in luminal Crohn's disease[END_REF][START_REF] Vermeire | Belgian Group of Infliximab Expanded Access Program in Crohn's Disease Demographic and clinical parameters influencing the short-term outcome of anti-tumor necrosis factor (infliximab) treatment in Crohn's disease[END_REF][START_REF] Arnott | An analysis of factors influencing short-term and sustained response to infliximab treatment for Crohn's disease[END_REF][START_REF] Subramanian | Recent advances in clinical practice: a systematic review of isolated colonic Crohn's disease: the third IBD?[END_REF]. The mechanisms remain unclear and a genetic influence is suspected [18; 19]. Thereby, recent evidence has suggested that CD with ileal involvement (ileal and ileocolonic) and isolated colonic CD should be considered as separate conditions [START_REF] Subramanian | Recent advances in clinical practice: a systematic review of isolated colonic Crohn's disease: the third IBD?[END_REF]. Up to now, the contribution of IBD location on the response to VDZ remains unclear.

In the pivotal clinical randomized trials on VDZ in CD (GEMINI II study), there was no significant difference in term of effectiveness in isolated colonic disease compared with other disease locations [8; 18]. Nevertheless, the authors of a recent study reported that clinical response in CD was higher in isolated and moderately active ileal disease location, compared to isolated colonic and ileocolonic location. Concerning UC, higher clinical response has been observed in less extensive locations than in pan UC [START_REF] Christensen | Vedolizumab in the treatment of IBD: The University of Chicago experience[END_REF].

These poorly consistent results and the huge lack of evidence regarding the role of IBD disease location on therapeutic response to VDZ therapy justified carrying out our study.

Our goal was to determine whether a colonic location (versus ileal) for CD and a distal location (versus extensive) for UC were predictive factors of steroidfree clinical remission at 6 months, under VDZ therapy, in real world settings.

PATIENTS AND METHODS

Study population

All adult IBD patients having received a VDZ induction therapy between October 2014 and June 2017 in 2 IBD referral centers (Grenoble and Lyon-Sud University Hospital) were included. The patient's charts were retrospectively reviewed from medical records. The Harvey-Bradshaw index (HBI) for CD [START_REF] Harvey | A simple index of Crohn's-disease activity[END_REF] and the partial Mayo clinic score (PMS) for UC [START_REF] Peyrin-Biroulet | Defining Disease Severity in Inflammaory Bowel Diseases: Current and Future Directions[END_REF] were used to assess disease activity. Active disease was defined as a HBI > 4 for CD and a PMS>1 for UC and/or concomitant CS medication. [START_REF] Peyrin-Biroulet | Defining Disease Severity in Inflammaory Bowel Diseases: Current and Future Directions[END_REF][START_REF] Peyrin-Biroulet | Selecting Therapeutic Targets in Infl ammatory Bowel Disease (STRIDE): Determining Therapeutic Goals for Treat-to-Target[END_REF][START_REF] Adedokun | Association between serum concentration of infliximab and efficacy in adult patients with ulcerative colitis[END_REF][START_REF] Rutgeerts | Infliximab for Induction and Maintenance. Therapy for Ulcerative Colitis[END_REF][START_REF] Vermeire | Correlation between the Crohn disease activity and Harvey-Bradshaw indices in assessing Crohn's disease severity[END_REF].

Clinical assessment and end points

The primary outcome measure was the percentage of patients in steroidfree clinical remission (CR) at week 24 for both CD and UC. Steroid-free CR was defined as an HBI score  4 for CD patients and a PMS  2 with each sub-score of 1 or less for UC [START_REF] Peyrin-Biroulet | Defining Disease Severity in Inflammaory Bowel Diseases: Current and Future Directions[END_REF][START_REF] Peyrin-Biroulet | Selecting Therapeutic Targets in Infl ammatory Bowel Disease (STRIDE): Determining Therapeutic Goals for Treat-to-Target[END_REF][START_REF] Adedokun | Association between serum concentration of infliximab and efficacy in adult patients with ulcerative colitis[END_REF][START_REF] Rutgeerts | Infliximab for Induction and Maintenance. Therapy for Ulcerative Colitis[END_REF][START_REF] Vermeire | Correlation between the Crohn disease activity and Harvey-Bradshaw indices in assessing Crohn's disease severity[END_REF]. CS had to be stopped at least 1 month before the evaluation to consider the CR as steroid-free. When HBI scoring was impossible (stoma, pouch), evaluation of clinical remission was performed by stoma emptying count and/or physician global assessment.

Patients having discontinued VDZ therapy whatever the reason during the 6 first months as well as patients referred to surgery and patients lost to follow up before week 24 were considered as failure to VDZ therapy and classified in the group of patients having failed to achieve steroid free clinical remission.

Disease location

The disease location was defined from recorded patient medical charts, according to the Montreal classification and was assessed by endoscopy and/or bowel imaging (MRI, CT) at diagnosis and during disease history. In CD, inflammatory lesions can be isolated to ileum (L1: ieal) or colon (L2: colonic) or both (L3: ileocolonic). In UC, inflammation can be limited to the rectum (E1:

ulcerative proctitis), to a proportion of the colorectum distal to the splenic flexure (E2: Left sided UC) or extended to the proximal colon above the splenic flexure (E3: extensive UC) [START_REF] Satsangi | The Montreal classification of inflammatory bowel disease: controversies, consensus, and implications[END_REF].

Active perianal CD was defined as simple or complex perianal fistula and/or ulcerations and anal stenosis. All patients underwent clinical examinations, magnetic resonance imaging (MRI) to classify the type of fistula, and also endoscopy for the evaluation of rectal inflammation. Complex fistulas were defined as high (high intersphincteric, high transphincteric, suprasphincteric, or extrasphincteric) with either multiple external openings associated with such pain or fluctuation suggesting a perianal abscess, or with a rectovaginal fistula or anorectal stricture. The therapeutic management of perianal CD was made by the physician but fistula tracks were systematically treated by curettage, irrigation with saline, and apposition of loose seton to facilitate drainage; the seton drain was removed after VDZ induction if sepsis was not present. If there was no response, the seton was left in place [START_REF] Peyrin-Biroulet | gastroenterologist nominal group French national consensus clinical guidelines for the management of Crohn's disease[END_REF].

Statistical analysis

All included patients were evaluated at week 24 and analyzed on an intentto-treat basis in our study.

Categorical variables were expressed as a number (%) and compared using a Chi-square test whereas continuous variables were expressed as a mean +/-the standard deviation (SD) and compared, using Student's t tests. P values inferior to 0.05 were considered significant. Receiver operative characteristic (ROC) curves analyses were performed to identify the best cut-off points of clinical scores and biological parameters which could predict a steroid-free clinical remission at 6 months. When a relative risk (RR) was determined, the associated sensitivity (Se), specificity (Sp), positive predictive value (PPV), and negative predictive value (NPV) were reported.

All statistical evaluations were performed with the SPSS software. All authors had access to the study data and reviewed and approved the final article.

RESULTS

Study population

Two hundred and twenty five IBD patients (133 CD, 92 UC), with moderate to severe disease, mainly refractory to anti-TNF therapy and exposed to VDZ therapy, were recorded between 2014 and 2017. Two UC patients were excluded from the study: one presenting with undetermined colitis and one with pouchitis.

Ninety UC patients treated with VDZ were finally analyzed. Among those 90 UC patients, 2 patients were lost to follow up during the study period and were considered as failure to VDZ therapy.

VDZ was administered intravenously, according to the standard recommendations, and all IBD patients received an infusion of VDZ 300 mg at week 0, 2, 6 (induction regimen), and then once every 8 weeks thereafter (maintenance regimen). If there was no clinical response at week 6, patients received an additional infusion of 300 mg VDZ at week 10, and then once every 4 weeks (intensification dose) according to daily practice.

The demographic, clinical, biological, and endoscopic characteristics, as well as medication history and concomitant therapies are summarized in tables 1 and 2., The ileocolonic location (L3) was the most frequent (67%) in CD patients whereas isolated ileal location (L1) and isolated colonic location (L2) accounted for 22% and 11% of patients, respectively. Proctitis (E1), left sided colitis (E2), and extensive disease (E3) were reported in 3%, 31%, and 66% of UC patients, respectively.

The mean disease duration in CD patients was 14.2 ± 0.9 years (yrs) and in UC patients 8.7 ± 0.8 yrs. Seventy two CD patients (54%) underwent an intestinal resection. One hundred and seven CD patients (98%) and 85 UC patients (95%)

had received at least one (and most several) prior lines of anti-TNF therapies.

Among these, 64% of CD patients and 43% of UC patients had received at least 2 anti-TNF agents. The few IBD patients who had not received any anti-TNF agents were those for whom these were contraindicated.

At week 0, only 37 CD patients (29%) and 25 UC patients (28%) were under VDZ monotherapy whereas VDZ was given at the onset of therapy with concomitant corticosteroid therapy for most of them (74 CD (57%) and 48 UC (54%)). An immunosuppressant was associated to VDZ in 40 CD (31%) and in 28 UC (31%) patients. Finally, 20 CD (20%) and 21 UC (24%) patients received concomitant immunosuppressive therapy for more than 3 months in addition to VDZ infusion.

At baseline (week 0), the mean HBI score was 8.3 ± 0.5 points in CD patients and the mean PMS was 6.0 ± 0.2 points in UC patients.

Steroid-free clinical remission at week 24

At 6 months (week 24), steroid-free CR was achieved in 33.1 % (n=44/133) CD patients and 33.3% (n=30/90) UC patients.

VDZ was discontinued in 19 CD patients (14%) (lack of efficacy, n = 16; drug-intolerance, n = 3) who were switched to an alternative therapy, whereas 4 patients (3%) were referred to surgery before week 24. VDZ was discontinued in 5

UC patients (6%) for lack of efficacy (no case of drug-intolerance) whereas 7 patients (8%) were referred to surgery before week 24 for VDZ refractory disease.

All those patients were considered as having failed to achieve steroid-free CR.

The characteristics of patients having achieved steroid-free CR at week 24 compared to those having failed are summarized in tables 3 and 4.

Relationship between disease location and steroid-free clinical remission at week 24 under VDZ therapy

Steroid-free CR assessed at week 24 under VDZ therapy was achieved in 33%, 36%, and 35% of CD patients, respectively for L1, L2, and L3 disease locations (p=0.906) (Fig. 1A). Furthermore, the rate of patients in steroid-free clinical remission was quite similar when isolated colonic disease (L2) was compared to ileal disease (L1 and L3) (p=0.928) (Fig. 1B).

Twenty-nine out of the 133 CD patients (22%) presented with an active perianal disease at the initiation of VDZ therapy (week 0). Most presented with a simple or complex perianal fistulizing disease, isolated in most cases (n= 18; 67%), associated with anal stenosis (n= 4; 15%), associated with anal ulcers (n= 3; 11%), and associated with anal stenosis and ulcer (n=2; 7%). Perianal abscesses were observed in 8/27 cases (30%) before or at baseline. At week 0, 5 out of 29 patients with perianal disease (17%) were already in stoma for discharge. A significantly lower rate of patients with active perianal CD achieved steroid-free CR at week 24 when compared to CD patients who do not exhibit active perianal disease (17% versus 42%) (p= 0.037) (Fig. 2B). The rate of patients under combination therapy with an immunosuppressant drug was similar in both active perianal disease and patients without active perianal disease (p= 0.528).

Steroid-free CR at week 24 was achieved in 37% of UC patients with distal locations (E1 or E2) and in 31% of those with extensive diseases (E3), p=0.594 (Fig. 3).

Relationships between baseline disease clinical activity, CRP, serum albumin, and fecal calprotectin, and the occurrence of steroid-free clinical remission at week 24

The baseline mean HBI score measured at the onset of VDZ was significantly lower in CD patients having achieved steroid-free CR at week 24 (6.4 ± 0.6 points) compared to that of patients who had failed (9.4 ± 0.6 points), (p=0.005). A baseline HBI score ≥ 10 points was associated with a high risk of failure to achieve steroid-free CR assessed at week 24 (RR = 1.45, 95%CI [1.15-1.84], Se = 36%, Sp = 87%, PPV = 84%, NPV = 42%).

No significant difference was observed for serum CRP, serum albumin and fecal calprotectin levels measured at the onset of VDZ therapy in CD patients who had achieved steroid-free CR at week 24 when compared with those who had failed.

The baseline mean PMS was significantly lower in UC patients who had achieved steroid-free CR at week 24 (5.5 ±0.3 points) compared to that of patients who had not (6.3 ± 0.2 points), (p=0.033). A PMS score ≥ 7 points was associated with high risk of failure to achieve steroid-free CR at week 24 (RR = 1.34, 95%CI = [1.02-1.77], Se = 83%, Sp = 38%, PPV = 25%, NPV = 90%).

A significant difference in serum CRP levels at week 0 was observed in UC patients having achieved steroid-free CR at week 24 (11.2 ± 2.8 mg/l) compared with those of patients who had not (21.5 ± 3.4 mg/l). A baseline serum CRP >20 mg/l was predictive of failure to achieve steroid-free CR at week 24 (RR = 1.29, 95%CI = [0.97-1.70], Se = 81%, Sp = 37 %, PPV = 28%, NPV = 86%).

But we failed to detect any difference in baseline serum albumin and fecal calprotectin levels between patients who had achieve steroid-free CR at week 24 under VDZ compared with those who had not.

Relationships between disease clinical activity, CRP, serum albumin, and fecal calprotectin measured at week 14 after VDZ initiation and the occurrence of steroid-free clinical remission at week 24

A significantly lower HBI score was recorded at week 14 in CD patients having achieved steroid-free CR at week 24 (1.9 ± 0.3 points) compared to those who had failed (7.6 ± 0.6 points), (p < 0.001). As illustrated in Figure 6.A, the optimal threshold for HBI score allowing to identify accurately remitted patients from non-remitted patients assessed at week 24, was 4 points, with RR=2.82, 95%CI [1.91-4.17], Se=73%, Sp=88%, PPV=90%, NPV=68% (AUROC=0.88).

Indeed, 88% of patients with an HBI score ≤ 4 points at week 14 had reached steroid-free CR at week 24 compared to 11% with an HBI score > 4 points (p<0.001).

The CRP level was significantly lower in CD patients having achieved steroid-free CR at week 24 compared with those who had not (7.9 ±1.7 mg/l vs 15.1 ± 2.2 mg/l), (p<0.001). Figure 6.B is the ROC curve illustrating the performance of CRP level at week 14 to predict steroid-free CR at week 24 in CD (AUROC=0.65).

A significantly lower PMS (1.9 ± 0.3 points) at week 14 was found in UC patients having achieved steroid-free CR at week 24 compared with those who had failed (4.5 ± 0.3 points), (p<0.001). As illustrated in Figure 7, a threshold at 2 points for PMS calculated at week 14 allowed prediction of steroid-free CR at week 24 with RR= 2.83, 95%CI [1.73-4.64], Se=80%, Sp=85%, PPV=92%, NPV=67% (AUROC= 0.85).

The levels of serum CRP, serum albumin, and fecal calprotectin measured at week 14 were quite similar in both groups of UC patients who achieved or not steroid-free CR at week 24.

Relationship between prior and concomitant therapies in addition to

VDZ and the occurrence of steroid-free clinical remission at week 24

An immunosuppressant was associated to VDZ therapy in 13/44 CD patients (29%) having achieved steroid-free clinical remission at 6 months and in 27/89 patients (33%) who had not (p=0.697).

There was no statistical difference in the rate of UC patients under combotherapy (VDZ and concomitant immunosuppressants) having achieved steroid-free CR at week 24 and those who had not: 8/29 (28%) and 20/61 (34%), respectively (p=0.55).

Only 25% of patients having achieved steroid-free CR at week 24 were under steroids at week 0 compared to 49% in non-remitted patients (p=0.005).

We further address the potential impact of the previous number of lines of anti-TNF on the probability to reach steroid free clinical remission: there was no difference in steroid-free CR at week 24 in patients who had received 0 or 1 anti-TNF compared to patients who had received 2 or more anti-TNF drug before VDZ, and this was the case for CD patients (p = 0.273) as for UC patients (p = 0.253).

Relationship between disease duration and the occurrence of steroidfree clinical remission at week 24 under VDZ therapy

CD duration at onset of VDZ therapy was around 14.7 ± 1.8 yrs in patients having achieved steroid-free CR at week 24 and 13.7 ± 1.1 yrs in patients who had not (p=0.605). The disease duration was also similar in both UC groups, respectively: 9.4 ± 1.3 yrs and 8.6 ±1.0 yrs (p=0.77). In addition, the rate of steroid-free CR at week 24 was similar in patients with early CD or UC (diagnosis < 2 years) and in patients with longer disease duration (p = 0.591 in CD; p=0.227 in UC)).

DISCUSSION

This retrospective study performed in a real life setting, highlights several key clinical observations on VDZ therapy in moderate to severe IBD patients, refractory to anti-TNF for the vast majority. The primary endpoint was steroid-free CR assessed 6 months after VDZ onset, which represents the ultimate clinical goal in IBD outcome [START_REF] Peyrin-Biroulet | Selecting Therapeutic Targets in Infl ammatory Bowel Disease (STRIDE): Determining Therapeutic Goals for Treat-to-Target[END_REF]. We investigated the influence of various clinical and laboratory parameters measured at baseline and at the end of the induction regimen (week 14) on the occurrence of steroid-free CR at week 24. The effectiveness of VDZ therapy to induce steroid-free CR at 6 months in our study was similar in CD (33.1 %) and in UC patients (33.3%). Our findings correlate to those of pivotal studies. Indeed, in the GEMINI clinical trials, respectively 31% of CD patients and 45.2% of UC patients achieved steroid-free CR at 1 year [7; 8].

The data obtained in the whole prospective and retrospective "real-world" studies conducted later was consistent with GEMINI results since the steroid-free CR rates under VDZ maintenance regimen ranged from 27 to 34% in CD and around 41% in UC at 1 year [10; 30].

Based on these results and on the data of clinical response at weeks 6 (31.4% for CD and 47.1 for UC patients) in the GEMINI trials, it was initially considered that the benefits of VDZ were more marked in UC patients than in CD patients [7; 8; 11; 31]. It was suggested that the transmural inflammatory lesions and systemic inflammatory burden in CD could limit the efficacy of VDZ therapy [11; 31; 32].

We failed to detect any difference in the rate of steroid-free CR for CD and UC patients. Several hypotheses may be raised: firstly, our very selected and complex IBD cohort was characterized by a long disease duration (mean 14.2 ± 0.9 yrs) for CD and 8.7 ± 0.8 yrs for UC) and several previous therapeutic lines, especially anti-TNF antagonists (at least 2 prior anti-TNF agents in most CD and UC patients) that could reflect long-lasting and refractory diseases unlikely to be easily controlled by medical therapy. Moreover, the baseline high clinical score as well as a high inflammatory burden highlighted by elevated serum CRP were associated with high risk of therapeutic failure under VDZ maintenance therapy in UC patients.

In the literature, steroid-free CR rates at week 14 were reported to be similar in CD and UC patients: from 18.8 to 31% in CD patients, and 19.1 to 36% in UC patients [11; 33-36]. The remission rates improve progressively between 3 months and 1 year since an incremental benefit with ongoing VDZ therapy has been suggested [START_REF] Dulai | The Real-World Effectiveness and Safety of Vedolizumab for Moderate-Severe Crohn's Disease: Results From the US VICTORY Consortium[END_REF].

Steroid-free CR at 6 months had never been evaluated for UC patients and only one study is available for CD patients: the US Victory Consortium study [START_REF] Dulai | The Real-World Effectiveness and Safety of Vedolizumab for Moderate-Severe Crohn's Disease: Results From the US VICTORY Consortium[END_REF] whose authors reported steroid-free CR rates of 18% at 6 months and 34% at 1 year, indicating cumulative remission rates during a continuous treatment with VDZ between 6 and 12 years. In this study, the median time to achieve remission ranged around 25 weeks. Therefore, a minimum of 6 months of treatment should be achieved before evaluating clinical remission and guiding the decision to optimize VDZ in case of insufficient efficacy.

The CD location (L1, L2 or L3), did not influence steroid-free CR at 6 months. In addition, no difference was observed when isolated colonic disease was compared to ileal location (isolated or associated with colonic location). On the other hand, no influence of UC location (distal versus extensive) was highlighted. Such insignificant results could be explained by the lack of statistical power since only 14/133 patients (11%) presented with an isolated colonic CD, and since distal disease accounted for only 1/3 of the UC population (31/90 patients). Moreover, our study had limitations, especially because of its retrospective design. Furthermore, it could be supposed that the primary endpoint and/or the timing of disease outcome were not the most appropriate to assess the impact of disease location on VDZ effectiveness. Finally, the characteristics of IBD patients may explain this absence of difference between locations: the frequent clinical and endoscopic severity for UC patients, even for distal locations, the frequent aggressive behavior of the disease (stricturing and/or fistulizing in 71% of CD patients), and the frequent gut anatomy modifications due to multiple IBD surgeries (more than 80% of the CD patients had a past history of surgery). It is assumed that CD location is closely correlated with the course of the disease and age at onset [15; 18]. That is why the association observed between colonic CD and response to induction of anti-TNF therapies could result more from the global disease characteristics than from the exclusive contribution of the disease location.

Even if a role of the  4  7 -integrins has been established, the precise mechanisms controlling homing of T effector and T regulator lymphocytes to the inflamed gut in CD and UC remain unclear from a pathophysiologic point of view.

As suggested by a study on in vitro and in vivo models, T effector lymphocyte homing mechanisms, in particular involvement of  4  1 -integrins, were reported distinct between ileal and colonic inflamed intestinal mucosa [START_REF] Zundler | The α4β1 Homing Pathway Is Essential for Ileal Homing of Crohn's Disease Effector T Cells In Vivo[END_REF]. However, more studies are required to understand these potential consequences on VDZ efficacy.

On the other hand, an influence of gut microbiome on the response to VDZ has been recently suggested in CD and UC patients. Indeed, associations between taxonomic composition and function at baseline and clinical remission at week 14 were identified [START_REF] Ananthakrishnan | Gut Microbiome Function Predicts Response to Anti-integrin Biologic Therapy in Inflammatory Bowel Diseases[END_REF].

Nevertheless, even if luminal CD location did not seem to have an impact on the clinical remission rate, active pCD appeared to be correlated with treatment failure. It was a fistulizing disease in 67% of the cases, isolated or associated with stenosis or ulcers. About half of the pCD patients had undergone surgery at week 0 or before. Our study confirms the role of active perineal disease as a baseline predictor of failure to achieve clinical remission [START_REF] Dulai | The Real-World Effectiveness and Safety of Vedolizumab for Moderate-Severe Crohn's Disease: Results From the US VICTORY Consortium[END_REF].

According to our results, an active pCD associated with clinical severity according to the HBI score at week 0 in CD patients and clinical severity according to the partial Mayo score with a high systemic inflammatory burden at week 0 in UC patients seemed to be associated with less chance to achieve clinical remission at 6 months. Indeed, an HBI threshold of 10 and more and a partial clinical Mayo score of 7 and more seemed predictive of treatment failure, but with weak performances. Evidence has identified an HBI ≥ 10 and a global Mayo score ≥ 9 as factors associated with a pejorative response [START_REF] Amiot | Observatory on Efficacy and of Vedolizumab in Patients With Inflammatory Bowel Disease Study Group; Groupe d'Etude Therapeutique des Affections Inflammatoires du tube Digestif. Effectiveness and Safety of Vedolizumab Induction Therapy for Patients With Inflammatory Bowel Disease[END_REF]. It must be noted that clinical scores and CRP levels at week 0 in our study should be interpreted with caution because of the frequent concomitant use of corticosteroids which can alter these parameters. A higher rate of patients receiving CS at week 0 was observed in the non remission group, reflecting the initial clinical severity in this group.

The HBI score and partial clinical Mayo score were predictive factors for steroid-free clinical remission, among clinical and biological parameters at the end of the induction period. An HBI score > 4 for CD patients and a partial Mayo clinic score > 2 (absence of clinical remission) at week 14 predicted the absence of steroid-free CR at week 24, with relevant performances (Fig. 6 and7). CRP also appeared as a potential predictive factor in CD patients, but to a lesser extent since the analysis of performances was less convincing (Fig. 6B). These results are consistent with previous results showing that the absence of clinical remission at week 14 in CD patients and the absence of clinical response in UC patients indicated a low likelihood of clinical remission at 1 year, and that lower CRP levels at week 14 was a predictor of clinical remission at 1 year in CD and UC patients [START_REF] Stallmach | Vedolizumab provides clinical benefit over 1 year in patients with active inflammatory bowel disease -a prospective multicenter observational study[END_REF]. In another study, an early clinical response (week 6) was also found to be a predictor of steroid-free clinical remission [START_REF] Amiot | OBSERV-IBD study group and the GETAID. One-year effectiveness and safety of vedolizumab therapy for inflammatory bowel disease: a prospective multicentre cohort study[END_REF].

No benefit of combination therapy with a concomitant immunosuppressive drug for steroid-free clinical remission was observed. This correlates with data of clinical trials and real world cohorts [7-11; 34; 39]. In contrast, the benefit of concomitant immunosuppressive therapy was reported for anti-TNF antagonists in several trials [11; 40-42] and was secondary to a decrease of immunogenic mechanisms. The low rate of antibody formation with VDZ (3.7-4.1% of patients in the GEMINI studies) could explain this absence of benefit [7-9; 12]. Nevertheless, contradictory results have been reported in a retrospective study with a seeming predictive character of combination therapy for clinical response or remission at 1 year. However, these results were obtained in a selected population of patients who demonstrated an initial response to VDZ induction and should be confirmed by prospective studies [START_REF] Allegretti | Predictors of Clinical Response and Remission at 1 Year Among a Multicenter Cohort of Patients with Inflammatory Bowel Disease Treated with Vedolizumab[END_REF].

The main limitation of our study was the retrospective data collection from 2 different centers, with missing or imprecise data for some parameters. Moreover, even if patient populations were supposed to be similar in terms of demographic characteristics and disease severity, some differences in clinical practice between the 2 medical centers remained (evaluation of clinical and endoscopic remission, optimization during and after induction period). Although we tried to overcome these limitations by using objective parameters for outcomes measurements, the bias related to our study design may have influenced the results.

However, in spite of its limitations, a "real-life" assessment of effectiveness, safety, and predictors of remission seemed very important since it had previously been established that many IBD patients were not eligible for clinical trials assessing biological therapies (such as patients with an ostomy or an ileo-anal pouch for instance). Thus, because of the stringent selection criteria, patients enrolled in clinical trials are not entirely representative of those managed in routine clinical practice settings and generalization of the trial results to the whole IBD community could be discussed [34; 44].

In conclusion, in our study, the disease location did not appear to influence the VDZ effectiveness, except from active pCD which was associated with a lower remission rate at 6 months. A prospective study, based on the rigorous assessment of disease and flare locations thanks to endoscopic and radiologic evaluations should be made.

At week 14, clinical and biological predictors of steroid-free clinical remission at 6 months were identified.

Finally, an earlier initiation of VDZ for some patients (short disease duration, no more than 1 anti-TNF antagonist) could be appropriate: however, the strategies to appropriately select these patients need to be clarified.

FIGURES

CONCLUSION

Les maladies inflammatoires chroniques de l'intestin (MICI), Maladie de Crohn (MC, prévalence 322 / 100 000 en Europe) et Rectocolite Hémorragique (RCH, prévalence 505 / 100 000 en Europe), sont des maladies graves du sujet jeune, chroniques, invalidantes, responsables d'une morbidité élevée altérant la qualité de vie. Leur prise en charge représente un enjeu de santé publique car leur impact socio-économique est majeur du fait de la nécessité de traitements prolongés et coûteux.

La prise en charge actuelle des MICI est celle d'une médecine de précision, basée sur l'identification de facteurs prédictifs de réponse aux différentes thérapeutiques disponibles dans le but de choisir la stratégie thérapeutique la plus adaptée à chaque patient, en particulier en termes de coût/efficacité. Les thérapies systémiques actuelles (corticostéroïdes, immunosuppresseurs, anti-TNF) n'étant pas dénuées d'effets indésirables potentiellement sévères, de nouvelles molécules aux mécanismes d'action plus ciblés ont été récemment développées. Parmi elles, le Védolizumab (VDZ) est un anticorps monoclonal bloquant spécifiquement l'interaction entre les intégrines  4  7 des lymphocytes T activés circulants et les molécules d'adhésion endothéliales, empêchant ainsi la migration lymphocytaire vers la muqueuse digestive inflammatoire. Cette thérapie anti-migration leucocytaire a démontré son efficacité à induire et maintenir une rémission clinique dans 3 essais cliniques pivots.

Dans différentes études prospectives et rétrospectives, certains facteurs ont été associés à une moins bonne réponse au VDZ, tels que le tabagisme, l'exposition antérieure à un traitement anti-TNF, l'atteinte ano-périnéale et la sévérité clinico-biologique de la maladie. Il existe actuellement très peu de données concernant l'influence de la localisation de l'atteinte inflammatoire de la MICI sur la réponse au VDZ, alors que celle-ci a été identifiée comme facteur prédictif de réponse aux anti-TNF pour la MC et la RCH. L'objectif de ce travail était de déterminer si la localisation colique (versus iléale) pour la MC et distale (versus pancolique) pour la RCH sont des facteurs prédictifs de rémission clinique sans corticostéroïdes à 6 mois.

Pour la MC luminale comme pour la RCH, Il n'a pas été mis en évidence dans cette étude de différence de rémission entre les différentes localisations. L'atteinte colique dans la MC, pourtant considérée comme de phénotype moins agressif et associées à de meilleures chances de rémission avec les anti-TNF, n'apparait pas ici comme facteur prédictif de réponse au VDZ. Il en est de même pour la RCH étendue (pancolique), habituellement considérée comme un facteur péjoratif associé à un risque plus élevé de colectomie, versus la RCH distale. Pour expliquer ces résultats, nous pouvons supposer d'une part qu'il n'existe effectivement pas d'influence de la localisation sur la rémission sans CS à 6 mois sous VDZ, ou d'autre part que cette influence n'a pas pu être mise en évidence du fait des limitations de notre étude. En effets, son caractère rétrospectif peut être responsable d'une imprécision d'évaluation des certains paramètres. De même, les patients MICI inclus dans notre étude constituent une population très sélectionnée, suivie en centre spécialisé, présentant des maladies sévères, de longue durée d'évolution et de phénotype agressif, avec antécédents fréquents de résections chirurgicales et traitements médicamenteux multiples, toutes localisations confondues.

Dans la MC, même s'il n'existait pas de différence entre localisation luminale iléale et colique, notre étude a tout de même permis de confirmer l'influence de la maladie ano-périnéale active qui apparait clairement associée à des chances plus faibles de rémission clinique sous VDZ.

Grâce à cette étude menée sur une importante cohorte multicentrique, des résultats intéressants sur les performances prédictives de certains paramètres cliniques et biologiques ont pu être obtenus. En effet, pour la MC comme pour la RCH, il est apparu que l'absence d'obtention d'une rémission clinique (définie selon les scores d'activité validés) à la fin de la phase d'induction, soit à 14 semaines de traitement, était prédictif de l'absence de rémission sans corticostéroïdes à 6 mois. De même, dans la MC, une CRP élevée à la semaine 14 semble être associée à un risque d'échec, mais avec des performances moindres. Ces résultats constituent des outils utiles au clinicien pour apprécier les chances d'efficacité du VDZ dès la fin de la phase d'induction et guider l'adaptation thérapeutique précoce.

En conclusion, la localisation n'apparait pas dans cette étude comme un facteur prédictif d'efficacité du VDZ, en dehors de la localisation périnéale active qui est associée à moins de chances de rémission sans corticostéroïdes à 6 mois. Une étude prospective, avec caractérisation rigoureuse des localisations de la maladie apparait nécessaire pour confirmer ces résultats.

Le rôle du clinicien, aidé de scores validés, reste majeur pour la prédiction des chances de rémission sans corticostéroïdes à 6 mois.

  (IBD), Crohn's Disease (CD), and Ulcerative

Figures 4

 4 Figures 4 and 5 are the ROC curves illustrating the respective performances of the clinical disease activity scores (HBI for CD patients and PMS for UC patients) and the baseline serum CRP level in UC patients to predict steroid-free CR at week 24 under VDZ therapy (AUROC= 0.68, 0.64 and 0.64, respectively).

Figure 3 -

 3 Figure 3 -Steroid-free clinical remission at week 24 in UC patients according to disease location. Comparison between distal (E1, E2) and extensive (E3) UC.

Figure 4 -

 4 Figure 4 -Performances of the HBI score at week 0 in CD patients for the prediction of steroid-free clinical remission at week 24. AUC = 0.68. A score ≥ 10 was associated with failure to achieve steroid-free clinical remission at week 24 with RR = 1.45, 95%CI = [1.15-1.84], Se = 36%, Sp = 87%, PPV = 84%, NPV = 42%.

Figure 7 -

 7 Figure 7 -Performances of Partial Mayo clinic score at week 14 in UC patients for the prediction of steroid-free clinical remission at week 24. AUC = 0.85 A score > 2 was associated with failure to achieve steroid-free clinical remission at week 24 with RR = 2.83, 95%CI = [1.73-4.64], Se = 80%, Sp = 85%, PPV = 92%, NPV = 67%.

Table 2 - Biological characteristics of the 223 IBD patients at baseline (week 0).

 2 Variables are presented as mean +/-standard derivation (SD).

	Steroid-free	No steroid-free
	clinical remission	clinical remission
	n = 44	n = 89	p value

Table 3 - Baseline characteristics of CD patients demonstrating steroid-free clinical remission under VDZ at week 24 compared to those with no steroid-free clinical remission.

 3 Continuous variables are presented as mean +/-standard deviation (SD) and categorical variables are presented as raw number and percentage (%).

	Steroid-free	No steroid-free
	clinical remission	clinical remission
	n = 29	n = 61	p value

Table 4 - Baseline characteristics of UC patients demonstrating steroid-free clinical remission under VDZ at week 24 compared to those with no steroid-free remission.

 4 Continuous variables are presented as mean +/-standard deviation (SD) and categorical variables are presented as raw number and percentage (%).

. Luminal and perineal surgery, 26

.

Table 1 -

Demographic and disease characteristics, previous and concomitant medication of the 223 IBD patients at baseline (week 0).

Continuous variables are presented as mean +/-standard deviation (SD) and categorical variables are presented as raw number (n) and percentage (%).

A.

B.