Soline Leblanc
email: soline.leblanc@ehesp.fr

J Roux

H Tillaut

E Le Page

E Leray

Disease-modifying therapy usage in patients with multiple sclerosis in France: a 6-year population-based study

Keywords: Multiple sclerosis, disease-modifying therapies, health administrative database, neurologists, state sequence analysis

Background: Most data regarding the use of disease-modifying therapies (DMTs) in multiple sclerosis (MS) comes from clinical series or regional databases that have a risk of recruitment bias. French health administrative data offers the significant advantage of being extensive in regards to both MS population coverage and DMT prescriptions.

Objectives: To describe patterns of DMTs usage at the level of the entire French population of MS patients from 2010 to 2015.

Methods: MS patients were identified during a 6-year study period via the French national health data system (covering 97% of the general population) and characteristics of patients who received at least one treatment were compared to those that never received treatment over the indicated period. A state sequence analysis was performed to study in a longitudinal way MS patients who started DMTs in 2010 and then to classify them into groups of similar therapeutic patterns. DMTs were categorized into firstline, second-line and off-label use, and included untreated periods for at least six months. Groups that were obtained were described and compared using a multinomial logistic regression.

Results: A total of 112,415 patients with MS were identified, of whom 54.0% received at least one DMT over the 6 years. The probability of being treated significantly decreased with age. Comorbidities and physical limitations appeared to be more frequent in not treated patients than in treated patients.

Significant differences were also found between the two groups regarding the use of healthcare services (hospitalizations and visits to general practitioner, neurologist and nurse). Based on the 6-year therapeutic sequences, a four-cluster typology was obtained on the 4,474 patients who started a DMT in 2010. The first group which consisted of more than half of the patients (57.0%) mainly used first-line DMTs. The second group (13.1%) represented patients with second-line DMTs whereas the third group (7.3%) was comprised of off-label users and the last group (22.6%) was composed of MS patients who received no or minimal treatments. Classification into one of these groups was associated with patient's age, long-term disease status, pregnancy occurrence, estimated level of disability, levels of care (visits to a neurologist, nurse and/or physiotherapist and hospital/rehabilitation stays) and occurrence of death.

Conclusions:

The exhaustive population-based dataset from the French national health data system gave the opportunity to provide a detailed description regarding the use of DMTs for MS at national level.

The innovative method of state sequence analysis allowed obtaining four homogeneous groups of patients among thousands of longitudinal therapeutic sequences. The predominant place of first-line treatments was confirmed even if the type of first-line treatments has probably changed since 2015.

Introduction

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system which affects 2.8 million people worldwide [START_REF] Walton | Rising prevalence of multiple sclerosis worldwide: Insights from the Atlas of MS, third edition[END_REF] . There is currently no cure for MS, however, around 15 diseasemodifying therapies (DMTs) which are only prescribed by neurologists in France are now available [START_REF] Vargas | Tyor WR Update on disease-modifying therapies for multiple sclerosis[END_REF] with the purpose of reducing the occurrence of relapse and delaying disability progression. DMTs can be classified according to their order in the therapeutic strategy (first-line, second-line and off-label use) or by their mode of administration (subcutaneous injections, intravenous infusions and oral pills) [START_REF] Vermersch | Chapitre 17. Traitements de fond et leurs complications[END_REF] . As first-line treatments, beta-interferon or glatiramer acetate are administered by injection and delivered via pharmacy, and two oral treatments (dimethyl fumarate and teriflunomide) have been marketed in 2014. Other treatments, even if not MS-specific, may be prescribed with an off-label use such as azathioprine, methotrexate, and mycophenolate mofetil. For active MS with many relapses or for when a first-line treatment is not effective, a second-line treatment can be proposed. Administered orally, fingolimod is the only second-line treatment distributed at pharmacies. Natalizumab, alemtuzumab, cyclophosphamide and mitoxantrone are administered intravenously or orally in hospitals.

Increasing numbers and varieties of DMTs have led neurologists to modify treatments when needed for cases such as safety concerns or therapeutic failure. Discontinuation of a treatment may also be related to a patient's choice for convenience or for family planning. Regardless, these recent therapeutic advances have led to major changes in the attitude of patients and neurologists toward drug prescriptions [START_REF] Elsisi | Expenditure, Utilization, and Cost of Specialty Drugs for Multiple Sclerosis in the US Medicaid Population, 2008-2018[END_REF] .

Previous studies about DMTs in France were mainly effectiveness studies and came from clinical regional or national data with a lack of descriptive data about use of DMTs over time. In that context, the French health insurance database offers the opportunity to get a national population-based overview, on a large number of patients without any risk of recruitment bias but with a lack of clinical data. The primary objective of this study was to describe therapeutic sequences in MS patients from the treatment initiation in 2010 to the end of follow-up in 2015. The secondary objective was to describe characteristics of treated and never-treated MS patients over the 6-year period.

Materials and methods

Data source

Data from the French national health data system (Système National des Données de Santé; SNDS) [START_REF] Tuppin | Value of a national administrative database to guide public decisions: From the système national d'information interrégimes de l'Assurance Maladie (SNIIRAM) to the système national des données de santé (SNDS) in France[END_REF] was used which is an administrative database and covers about 97% of the general French population. It contains exhaustive individual data regarding the reimbursement of ambulatory healthcare procedures such as doctor consultations, biological tests and drug prescriptions. It also includes patient hospital activity (inpatient/outpatient visits), demographics data, general insurance coverage, universal health insurance plans (Couverture Maladie Universelle (CMU) which applies to specific low-income people) and medical characteristics such as long-term disease (LTD) which entitles a patient to 100% reimbursement for all medical costs. Individuals on the system are identified by a unique anonymized personal identifier. Ethical and data access approvals for the present study were obtained in accordance with applicable French legislation.

Study population

People with MS were identified from 2010 to 2015 using a three-criterion algorithm proposed by the French health insurance system [START_REF] Foulon | Prevalence and mortality of patients with multiple sclerosis in France in 2012: a study based on French health insurance data[END_REF] . Subjects were considered as having MS if they met at least one of the following criteria: (i) having at least one reimbursement for an MS-specific DMT (including betainterferon, glatiramer acetate, fingolimod, natalizumab, teriflunomide or dimethyl fumarate); (ii) having an active LTD status for MS, or (iii) having at least one hospital admission with a diagnosis of MS based on the International Classification of Diseases, 10 th version (ICD-10) G35 diagnosis code 7 . The date of MS identification was defined as the earliest date between the date of admission into LTD status for MS (potentially before 2010), the first date of hospitalization for MS or the first date of DMT prescription from 2010 to 2015 8 . To estimate some study inclusion parameters, data was extracted for the years from 2007 to 2015.

Firstly, the overall MS population was considered before focusing on MS patients who started a DMT in 2010 and had no DMT prescription over the period from 2007 to 2009. This was done to ensure a sixyear follow up for each patient over the period from 2010 to 2015 and to get the opportunity to explore their therapeutic patterns in a longitudinal way.

Data

Patients were considered as treated if they had at least one delivery of beta-interferon, glatiramer acetate, fingolimod, natalizumab, teriflunomide, dimethyl fumarate, azathioprine, methotrexate or mycophenolate mofetil over the study period. Neither mitoxantrone, nor cyclophosphamide and alemtuzumab were considered since they were not available in the hospital data. DMTs were grouped according to their level in therapeutic strategy: first-line (glatiramer acetate, beta-interferon, teriflunomide and dimethyl fumarate), second-line (natalizumab and fingolimod) and off-label use (mycophenolate mofetil, methotrexate and azathioprine). Only DMT treatment cessation of at least six months was considered.

The following patient characteristics were identified: gender, age at the start of the study (2010), region of residence, occurrence of death, insurance coverage (including CMU), LTD status and pregnancy occurrence. Pregnancies were identified through their outcome based on the last hospital stay for birth or abortion (diagnosis and/or medical procedures) which were derived from hospital databases or the last reimbursement transaction for a non-hospital medical abortion [START_REF] Blotière | Development of an algorithm to identify pregnancy episodes and related outcomes in health care claims databases: An application to antiepileptic drug use in 4.9 million pregnant women in France[END_REF] . The Charlson Comorbidity Index, adapted for French administrative databases [START_REF] Bannay | The best use of the Charlson comorbidity index with electronic health care database to predict mortality[END_REF] , was calculated based on data from the 12 months preceding the date of MS identification and categorized as a four-level score (0, 1-2, 3-4, ≥5). This score was found to predict the 1-year mortality [START_REF] Charlson | A new method of classifying prognostic comorbidity in longitudinal studies: Development and validation[END_REF] and was used here to approximate the general health status.

Patients were classified as missing if 12 months of data were not available.

In terms use of healthcare services, visits with general practitioners (GPs), neurologists, nurses and physiotherapists were considered. Hospitalizations in medicine, surgery and obstetrics wards (MSO) and rehabilitation wards (REHAB) were also analyzed. Hospitalizations corresponding to DMT injections were excluded from these analyses. Outpatient consultations performed in hospitals were also included and assigned by default to the GP category when the medical specialty was missing.

An approximated level of disability was computed based on prescriptions of technical aids at inclusion and categorized as follows: mild if the patient never had a technical aid, moderate if the patient had at least one prescription for a walking stick, walker or wheelchair, and severe if the patient had at least one prescription of a medical bed, a patient lift or an anti-pressure ulcer mattress.

Statistical analysis

Patients in the overall population who took at least one DMT over the study period were compared to patients who never received DMT using the Wilcoxon or Pearson chi-square tests when applicable. A multivariate logistic regression including parameters related to demographics and use of healthcare services was also performed. After that, a state sequence analysis [START_REF] Abbott | Sequence Analysis and Optimal Matching Methods in Sociology: Review and Prospect[END_REF][START_REF] Studer | Discrepancy Analysis of State Sequences[END_REF][START_REF] Roux | Use of state sequence analysis for care pathway analysis: The example of multiple sclerosis[END_REF] (SSA) was performed among the subgroup of patients who initiated a DMT in 2010 (without DMT from 2007 to 2009) to identify groups of similar patterns regarding the use of DMTs over the six-year time frame.

The general principle of SSA is to compare sequences regarding to the succession of their states. The term "sequence" referred to the entire individual therapeutic pathway and states were defined as the level in the therapeutic strategy of the DMTs prescribed. The four following states were considered: first-line, second-line, off-label use and no treatment. The time unit in the sequence was chosen as monthly, therefore, data was managed to assign one of these four states for each patient and each month.

When different states could be assigned to the same month, the first occurring state was considered. For periods without treatment of less than six months, the preceding state was assigned. An additional fifth state which was coded non-attributed (NA) was used for the states following the occurrence of death. This procedure created right-truncated sequences and avoided the creation of a specific cluster dedicated to patients who died. All patients had the same sequence length of 72 months, except for right-truncated sequences.

After creating individual therapeutic sequences, a two-by-two comparison of sequences was performed using the optimal matching (OM) method to measure dissimilarity between each couple of sequences [START_REF] Studer | What matters in differences between life trajectories: a comparative review of sequence dissimilarity measures[END_REF][START_REF] Robette | Harpoon or bait? A comparison of various metrics in fishing for sequence patterns[END_REF] . The matrix of substitution costs was estimated empirically using the transition rates observed in the dataset [START_REF] Biemann | Analyzing Sequence Data: Optimal Matching in Management Research[END_REF][START_REF] Gabadinho | Analyzing and Visualizing State Sequences in R with TraMineR[END_REF] . The dissimilarity matrix was used to cluster sequences and to create a typology of homogeneous patterns of DMT use with an agglomerative hierarchical clustering method using the Ward criterion [START_REF] Dlouhy | Optimal matching analysis in career research: A review and some best practice recommendations[END_REF] . The optimal number of clusters was chosen using the fall in inertia. All grouped sequences were visually presented on an index plot [START_REF] Dlouhy | Optimal matching analysis in career research: A review and some best practice recommendations[END_REF] .

Once the clusters were obtained, they were described and compared using a Kruskal-Wallis test, a Pearson chi-square test, or a Fisher exact test, where appropriate. A multinomial logistic regression [START_REF] Hosmer | Applied Logistic Regression[END_REF] was also performed. All computational and statistical analyses were performed with R v3.4.3 software [START_REF] Core | R: A language and environment for statistical computing[END_REF] . The sequence analysis and the clustering used the TraMineR library 2.2-0.1 [START_REF] Gabadinho | Analyzing and Visualizing State Sequences in R with TraMineR[END_REF] and the WeightedCluster library v1.4 [START_REF] Studer | WeightedCluster Library Manual: A practical guide to creating typologies of trajectories in the social sciences with R[END_REF] .

Results

Comparison of treated to untreated patients

Among the 112,415 patients identified as having MS in France, 54.0% received at least one DMT over the period. The most prescribed DMT was beta-interferon for more than half of treated patients, followed by glatiramer acetate which was prescribed for one quarter of these patients. The evolution in the use of DMTs from 2010 to 2015 is presented in Figure 1. The impact of the arrival of new oral treatments on the market is observable from 2012 for fingolimod, and from 2014 for dimethyl fumarate and teriflunomide. Use of DMTs over the study period differed somewhat between various French regions (Figure 2).

Figure 1 and 2 here

Number of women among treated patients (72.0%) was slightly higher than untreated patients (69.6%).

Treated patients were significantly younger with a median age in 2010 of 41 years versus 53 years for untreated patients. Accordingly, there was less occurrence of death over the study period in the treated group (1.6%) than in the untreated group (7.8%). The difference in the number of admissions for LTD for MS between the two groups (92.8% for treated patients versus 76.1% for untreated patients) most likely reflected the need for LTD status due to the high costs of DMT treatment. Additional characteristics are presented and compared between the two groups in Table 1 and differences between the two groups from the multivariate logistic regression model are summarized in Figure 3. DMT use was associated with lower age groups because the probability of being treated over the study period decreased significantly with age. Moreover, the Charlson Comorbidity Index and the approximated level of disability showed that health and physical limitations of untreated patients were worse than those of treated patients.

Figure 3 here

In addition, the use of healthcare services over the period was found to be different between the two groups (Table 1). There were more patients with at least one visit to a GP, neurologist or nurse among patients who received at least one DMT, while the number of patients with at least one visit to a physiotherapist was similar in the two groups. Moreover, the number of patients with at least one MSrelated hospitalization in MSO was significantly higher for treated patients (47.2%) versus 29.9% for untreated patients. The same was noted for MS-related hospitalizations in REHAB. However, the length of stay of MS-related hospitalizations per patient in MSO were similar for the two groups but the length of stay of MS-related hospitalizations in REHAB were slightly higher for untreated patients (5.8 days versus 7.2 days per patient-year, in median).

Table 1 here

Identification of homogeneous patterns of DMT use over time

Among treated patients, 4,474 initiated DMTs in 2010 after being untreated from 2007 to 2009. These patients had approximatively the same characteristics as the 60,693 treated patients described previously (Table 2). Among these 4,474 patients, 2,481 different 72-monthly therapeutic sequences were identified and compared. Their partitioning led to a four-cluster typology (Figure 4) which was helpful understanding therapeutic practices. Clearly, Cluster 1 predominantly contained more than half the patients and corresponded to patients who spent most of their follow-up under first-line DMTs with a median of 86.1% of the follow-up. Cluster 2 comprised almost one quarter of the patients who were mostly not treated (83.3% of the follow-up, in median) after a short period with either a first-line DMT or an off-label treatment (median of 12.5 and 13.9% of the follow-up, respectively). Patients in Cluster 3, which represented 7.3% of all the patients, had mainly prescriptions for off-label use treatments with a median of 81.9% of the follow-up. Finally, Cluster 4 represented 13.1% of the patients and most of them were treated by second-line DMTs (65.3% of the follow-up, in median). This period of second-line DMT treatment was preceded, for half of them, by a short first-line DMT treatment period that lasted, in median, only one quarter of the time.

Figure 4 and Table 2 here

Comparison of clusters

Patient characteristics, use of healthcare and DMTs are summarized for each cluster in Table 1. Cluster 1 was chosen as the reference group in the multinomial logistic regression since it comprised the largest part of the study population. Results are presented on Figure 5.

Compared to Cluster 1, patients in Cluster 2 (mainly not receiving DMTs) were older with a median age in 2010 of 44 years versus 38 years old. The approximated level of disability was higher and there were more occurrences of death over the study period in this cluster (4.0% versus 0.4%). There were fewer patients with at least one visit to a neurologist (91.5% versus 96.9%), while the number of patients with at least one visit to a physiotherapist was higher (57.1% versus 49.8%). In accordance, the probability of being in Cluster 2 in comparison to Cluster 1 was associated with higher age and estimated level of disability.

Patients in Cluster 3 (mainly treated using off-label treatments) were significantly older than patients in Cluster 1 (median age of 51 years old versus 38 years old in 2010). The number of patients with a moderate or severe level of estimated disability was also higher (36.9% versus 5.5%) and there were more occurrences of death in this cluster (4.9% versus 0.4%). The number of patients with at least one visit to a neurologist was similar in Clusters 3 and 1, while there were more patients with at least one visit to a physiotherapist in Cluster 3 (79.1% versus 49.8%). The probability of being in Cluster 3 compared to Cluster 1 was thus associated with higher age and estimated level of disability.

Patients in Cluster 4 (mainly on second-line DMTs) were slightly younger than patients in Cluster 1 with a median age of 35 years old. The number of patients who had visited a neurologist was very high (99.5%) and Cluster 4 had the highest rate of MS-related hospitalizations in MSO (80.5%). The probability of being in Cluster 4 compared to Cluster 1 was associated with younger age. Moreover, this probability was higher for patients who had visited a neurologist at least once.

Discussion

This study allowed a comparison to be made between patients with MS who were treated and untreated patients from 2010 to 2015 and was based upon the entire population of MS patients in France. Our study showed that patients who had not received DMT were older, used less healthcare services, and had a higher estimated level of disability. Some differences were found between French regions in the choice of DMTs over time, but interpretation should be cautious since no adjustment was done and these are crude results.

The primary objective of the study was to describe therapeutic practices among patients who initiated a treatment in 2010 and identify specific patterns of DMT usage. From the 2,481 different 6-year sequences identified among the 4,474 patients, a four-cluster typology was obtained from the state sequence analysis and indicated a correspondence with actual therapeutic practices according to MS phenotypes. Half the patients (Cluster 1) were treated with first-line DMTs that may reflect the most common form of MS, i.e. relapsing remitting MS (RRMS). A proportion of these patients needed to be treated with second-line DMTs due to an aggressive or active MS and/or first-line DMT failure. They were classified into Cluster 4 (13.1%). Cluster 4 also showed patients who directly started with a highly effective DMT, which was probably due to early negative prognostic factors. A small percentage of patients (7.3%), shown in Cluster 3, used off-label treatments which are not approved for MS and most likely corresponded to patients with a progressive form of MS. Lastly, a quarter of patients were not treated (Cluster 2) which was probably due to either the benign form of the disease or the evolved form of their disease which could be the most plausible hypothesis because patients appeared to be older and with higher disability than in the other groups. Moreover, although these patients were not treated during the six year study period, they may have received treatment earlier in the course of the disease, however data was unavailable before 2007.

To our knowledge, there are very few studies conducted on the entire population of MS patients in France that provide such a detailed description of DMT usage. A recent study was conducted in France using the same administrative database to assess real-world use of first-line DMTs in naïve patients with RRMS. Between September 1, 2014 and August 31, 2016, 10,240 patients starting a first-line DMT for RRMS were identified. Two-thirds of patients were mainly treated with oral forms (teriflunomide and dimethyl fumarate) and the other third with interferon and glatiramer acetate [START_REF] Vermersch | An analysis of first-line disease-modifying therapies in patients with relapsing-remitting multiple sclerosis using the French nationwide health claims database from 2014-2017[END_REF] . Another study was carried out between 2013 and 2015 dedicated to self-employer workers (Régime Social des Indépendants, RSI) that represents 6% of the French population [START_REF] Ha-Vinh | Health care services and disease modifying therapies use in community-based multiple sclerosis patients: Evolution from 2013 to 2015 and demographic characteristics[END_REF] . They found a DMT utilization rate increased due to recently developed DMTs (teriflunomide and dimethyl fumarate) while first-generation DMT (beta-interferon) utilization rate decreased. As in our study, they showed that DMT utilization significantly decreased with age and that there were significant variations according to French geographic regions.

In our study, the population came from a nearly exhaustive database of the French general population (97% coverage) with systematic data collection provided by the national health insurance system. It should be noted that neither mitoxantrone, nor cyclophosphamide were available in the database which may lead to misclassification of some patients who started DMT in 2010, however, this should not strongly impact the results since they are rarely prescribed. This population-based data allowed avoiding any recruitment bias and the opportunity to get complete follow-up over the six-year period. This may represent a significant advantage over clinical series or regional databases that may not be populationbased and recruitment through MS expert centers may led to more severe MS patients [START_REF] Debouverie | Earlier disability of the patients followed in Multiple Sclerosis centers compared to outpatients[END_REF] . However, the main limitation of the present study was the lack of clinical data, especially MS-related data such as EDSS (Expanded Disability Status Scale) scores, laboratory data or MRI results because the database was principally designed for administrative functions.

Due to the absence of neurologist-based data collection, several assumptions were required to be made.

The date of MS onset was approximated by the date of MS identification in the database. This approximation did not allow the whole therapeutic sequence from MS onset to be analyzed. This is the reason why therapeutic sequences started to be studied from the first initiation of treatment in 2010.

Since the date of DMT administration was not available (except for natalizumab), the date of delivery from pharmacists was used even if there may have been several days or weeks lag time between delivery and real intake. Moreover, the assumption that patients initiated their first treatment in 2010 was based on the absence of any DMT prescriptions over the period from 2007 to 2009. However, data were not available for some specific insurance plans during this period that indicates that around 10% of patients may have been classified as newly treated in 2010 when in fact they had been previously treated before.

This may have created a limited misclassification bias. Finally, the level of disability was approximated using prescription records for technical aids without knowing the precise applications of such materials. This approximation, however, was mainly based on the purchases of such equipment rather than shortterm rentals that may be caused by limited traumatic events instead of MS. In the same way, the Charlson Comorbidity Index was used to approximate the general health status as it identifies comorbid conditions that alter the risk of 1-year mortality [START_REF] Bannay | The best use of the Charlson comorbidity index with electronic health care database to predict mortality[END_REF][START_REF] Charlson | A new method of classifying prognostic comorbidity in longitudinal studies: Development and validation[END_REF] . This score is based on a list of 17 defined comorbidities and did not take into account all the patient's conditions.

A strength of this study was the use of SSA that is an innovative and flexible method that allows the whole therapeutic sequence to be considered in contrast to conventional approaches that analyze each state independently. Because MS onset dates were not available, the decision was made to start the therapeutic pathway analysis from January 2010 that allowed for the same length and left-aligned sequences except for deceased patients, hence, clustering may not have been driven by the length of the sequences. Furthermore, this work was based on calendar months and, periodically, different states could have been assigned to the same month that probably corresponded to a switch between DMTs. In this case, only the first DMT was considered and the second was considered in the next state. Moreover, the choice was made to consider only treatment cessations lasting at least six months. When precisely considering the months without treatment as a sensitivity analysis, similar clusters were obtained and showed only an 11% discrepancy. This may be explained by the larger number of distinct individual therapeutic sequences; 4,208 different sequences compared to 2,481 initially among the 4,474 patients. Such significant variability highlights the need for appropriate methods of partitioning to determine a relevant typology of therapeutic practices based on thousands of sequences summarized into only four comprehensive homogeneous clusters.

In conclusion, a clustering method on therapeutic sequences on a nationwide level to describe DMT prescriptions over a six year period was applied and four main clusters were found. Overall, more than half the patients (57%) were treated with first-line DMTs, 13% with second-line DMTs (either moving from first-line or starting directly with such highly effective therapies), 7% with off-label treatments and 23% who rapidly stopped treatment. Unfortunately, the dataset used was outdated due to the quickly evolving therapeutic progress in MS treatment. The present analysis is planned to be updated to include data up to 2019 that may offer an opportunity to better characterize current therapeutic practices and may show a potential increasing place of new drugs, such as anti-CD20 and S1P drugs.

Figure 5

 5 Figure 5 here

Figure 1 .

 1 Figure 1. Characteristics associated with treated status in multiple sclerosis (MS) patients over the period from 2010 to 2015 (N= 112,415)Forest plot of adjusted odds ratios (with 95% confidence intervals) obtained from a multivariate logistic regression analysis

Figure 2 .Figure 3 .Figure 4 .Figure 5 .

 2345 Figure 2. Use of multiple sclerosis-specific disease modifying therapies (DMTs) over the period from 2010 to 2015 (n= 60,693)

  p-value comparing the two groups treated with at least one DMT vs. untreated by the Wilcoxon or Pearson's chi-square tests; b Median (q1 -q3); c percentage calculated only for women; d approximated level of disability based on prescription of technical aids; e based on data from the 12 months preceding study entry (if available); f hospitalizations corresponding to DMT injections were excluded. MS = multiple sclerosis; CMU = universal health insurance (Couverture Maladie Universelle); MSO = medicine, surgery or obstetrics; REHAB = rehabilitation; DMT = disease-modifying therapy.

	Physiotherapist	61,332 (54.6%)	32,965 (54.3%)	28,367 (54.8%)	0.076
	At least one hospitalization in MSO, n (%)
	All diagnoses	92,007 (81.8%)	49,483 (81.5%)	42,524 (82.2%)	0.003
	MS-related f	44,125 (39.3%)	28,643 (47.2%)	15,482 (29.9%)	<0.001
	At least one hospitalization in REHAB, n (%)
	All diagnoses	27,236 (24.2%)	13,172 (21.7%)	14,064 (27.2%)	<0.001
	MS-related	20,117 (17.9%)	11,235 (18.5%)	8,882 (17.2%)	<0.001
	At least one DMT prescription of, n (%)				-
	Beta-interferon	--	31,871 (52.5%)	--
	Glatiramer acetate	--	15,329 (25.3%)	--
	Dimethyl fumarate	--	9,573 (15.8%)	--
	Fingolimod	--	8,941 (14.7%)	--
	Natalizumab	--	8,248 (13.6%)	--
	Teriflunomide	--	7,203 (11.9%)	--
	Mycophenolate mofetil	--	3,883 (6.4%)	--
	Azathioprine	--	3,713 (6.1%)	--
	Methotrexate	--	2,698 (4.4%)	--
	At least one prescription among, n (%)				-
	First-line	--	48,483 (79.9%)	--
	Second-line	--	14,154 (23.3%)	--
	Off-label use	--	9,506 (15.7%)	--
	Year of treatment start, n (%)				-
	Before 2010	--	32,952 (54.3%)	--
	2010	--	4,474 (7.4%)	--
	2011	--	4,477 (7.4%)	--
	2012	--	4,850 (8.0%)	--
	2013	--	4,209 (6.9%)	--
	2014	--	4,401 (7.3%)	--
	2015	--	5,330 (8.8%)	--

a

Table 2 .

 2 Characteristics of the four groups of naïve multiple sclerosis (MS) patients obtained by the clustering procedure over the period from 2010 to 2015 (n= 4,474) p-value comparing the four groups by the Kruskal-Wallis, Pearson's chi-square test, or Fisher's exact test; b Median (q1 -q3); c percentage calculated only for women; d approximated level of disability based on prescription of technical aids; e based on data from the 12 months preceding study entry (if available); f hospitalizations corresponding to DMT injections were excluded. MS= multiple sclerosis; CMU= universal health insurance (Couverture Maladie Universelle); MSO= medicine, surgery or obstetrics; REHAB= rehabilitation; DMT= disease-modifying therapy.

	Overall	Cluster 1 "First-line DMTs"	Cluster 2 "Not treated"	Cluster 3 "Off-label use"	Cluster 4 "Second-line DMTs"	p-value a
	4,474 (100.0%)	2,552 (57.0%)	1,011 (22.6%)	325 (7.3%)	586 (13.1%)

a

Acknowledgements

The authors acknowledge the Institut National des Données de Santé and the Commission Nationale Informatique et Libertés for use of their data (Authorization DE-2017-026) and would like to thank Sarina Yaghobian (AcaciaTools) for reviewing the manuscript.

Emmanuelle Leray reports research grants from the French National Agency for Medicines and Health Product Safety (ANSM), the EDMUS Foundation and the ARSEP Foundation; consulting and lecture fees or travel grants from Biogen, Genzyme, MedDay Pharmaceuticals, Merck Serono, Novartis, and Roche. Nothing related to the contents of the present work.

Funding

This work was supported by the "Institut des Neurosciences Cliniques de Rennes".

Contributors

EL and SL conceived and designed the study. SL performed the data analysis. SL wrote the first draft of the manuscript. EL, ELP, JR and HT provided revisions.

All authors participated in the interpretation of the results, and writing of the manuscript, and approved the decision to submit the final version of the paper for publication


MD Kévin Bigaut
email: kevin.bigaut@chru-strasbourg.fr

Laurent Kremer

Marie-Céline Fleury

Livia Lanotte

Nicolas Collongues

Jérôme De Sèze

Jérôme De Seze

Impact of disease-modifying treatments on humoral response after COVID-19 vaccination: A mirror of the response after SARS-CoV-2 infection

Keywords: Multiple sclerosis, COVID-19, Vaccine, Humoral response, Antibody

ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

The development of vaccines and the capacity to implement quick and large vaccination campaigns play a key role in COVID-19 pandemic control. The Pfizer-BioNTech (Brooklyn, NY, USA) and Moderna (Cambridge, MA, USA) COVID-19 mRNA vaccines received authorization by the European Medicines Agency in December 2020.

Among patients with multiple sclerosis (MS), those treated with anti-CD20 monoclonal antibodies (mAb) have a higher risk of severe COVID-19 leading to their being vaccinated as a priority [START_REF] Sormani | Disease-Modifying Therapies and Coronavirus Disease 2019 Severity in Multiple Sclerosis[END_REF][START_REF] Louapre | Clinical Characteristics and Outcomes in Patients With Coronavirus Disease 2019 and Multiple Sclerosis[END_REF]. However, a reduced humoral response was observed after tetanus, seasonal flu and pneumococcus vaccinations in this population. Only limited data are available on the immune response after COVID-19 vaccinations in MS patients [START_REF] Achiron | Humoral immune response to COVID-19 mRNA vaccine in patients with multiple sclerosis treated with highefficacy disease-modifying therapies[END_REF].

The objective of our study was to analyze the humoral response after COVID-19 vaccination in MS patients according to disease-modifying treatments (DMTs) and in comparison with the humoral response after COVID-19.

Methods

Patients

We included 28 MS patients with serological results after COVID-19 vaccination and 61 MS patients with serological results after COVID-19 between January and April 2021 from the MS center of Strasbourg, France.

All 28 vaccinated patients had received 2 doses of Pfizer-BioNTech or Moderna COVID-19 vaccine.

For the 61 MS patients with COVID-19, COVID-19 diagnostic criteria were: positive SARS-CoV-2 PCR on nasopharyngeal swab (40/61, 65.6%); or typical thoracic computed tomography (CT) abnormalities (ground-glass opacities) in epidemic areas (8/61, 13.1%); or anosmia or ageusia of sudden onset in the absence of rhinitis or nasal obstruction (23/61, 37.7%); or COVID-19 typical symptoms (triad of cough, fever and asthenia) in an epidemic zone of COVID-19 (43/61, 70.5%).

Collected data were: age, sex, disease-modifying treatment (DMT) at the time of vaccination or COVID-19 (anti-CD20 mAb, sphingosine 1-phosphate receptor [S1PR] modulator and other treatments) and the time between COVID-19 or COVID-19 vaccination and the serology.

The primary endpoint was the IgG index according to DMTs in the COVID-19 vaccine or COVID-19 groups.

SARS-CoV-2 antibody detection

Serum samples were tested using the Abbott or Roche SARS-CoV-2 IgG assay (spike protein). Tests were classified as positive if the index exceeded the threshold defined by the manufacturer (range of the threshold between 0.72 and 1.54 U/ml).

Standard Protocol Approvals, Registrations, and Patient Consent

This study was approved by local ethics committee. All patients gave written informed consent to be included in the cohort.

Statistical analysis

Descriptive analyses were performed with results presented as means (standard deviation) and median (interquartile range [IQR]).

Only univariate analyses were done because of the limited size of the population expected for serological response according to COVID-19 vaccine and COVID-19 groups, using a linear regression model adjusted for age, sex, time between the onset of COVID-19 or the first dose of the vaccine and the serology and the DMT group. For this multivariate analysis, as the distribution of residuals did not following a normal distribution, we calculated confidence intervals and p-value by bootstrap (1000 iterations) [START_REF] Medistica | .io, a graphic user interface to the R statistical analysis software for scientific medical publications[END_REF].

Results

We included 28 MS patients in the COVID-19 vaccine group and 61 MS patients in the COVID-19 group.

Descriptive analysis

The descriptive analysis is summarized in Table 1. The proportion of patients treated with anti-CD20 mAb was higher in the COVID-19 vaccine group (11 patients [39%]) than in the COVID-19 group (5 patients [8.2%]; p<0.01). Patients treated with anti-CD20 mAb were more often vaccinated than other patients, due to the recommendations of the French National Authority for Health prioritizing this population at a higher risk of severe COVID-19 [START_REF] Sormani | Disease-Modifying Therapies and Coronavirus Disease 2019 Severity in Multiple Sclerosis[END_REF][START_REF]La stratégie vaccinale et la liste des publics prioritaires[END_REF]. The delay between the onset of COVID-19 and serology was greater than the delay between the first dose of the vaccine and serology, due to the unavailability of serology during the first wave of the outbreak.

Humoral response after COVID-19 vaccination and COVID-19

In vaccinated MS patients, the median IgG index was lower in patients treated with anti-CD20 mAb and in patients treated with S1PR modulator compared to patients receiving other or no DMT (4.80 2). A similar result was found for MS patients after COVID-19 (Table 2).

In the multivariate analysis, no differences were found between the IgG index in MS patients after COVID-19 vaccination and MS patients after COVID-19 (coefficient = 649 [-2622; 3918], p=0.58).

Sensitivity analysis

Among the 11 patients treated with anti-CD20 mAb, patients vaccinated in 4 months from the last infusion had a weak humoral response (figure). After 4 months, 2/3 patients developed a humoral response and the patient with a low IgG index had anti-CD20 mAb infusion between vaccination and the serology (37 days after the first dose of vaccine and 15 days before the serology) probably influencing the result.

Discussion

Our study showed a reduced humoral response after COVID-19 vaccine in MS patients treated with anti-CD20 mAb or S1PR modulator compared to other patients. These results mirrored the humoral response in MS patients after COVID-19.

Patients treated with anti-CD20 mAb or S1PR modulator had a reduced humoral response to pneumococcal or seasonal influenza vaccines [START_REF] Bar-Or | Effect of ocrelizumab on vaccine responses in patients with multiple sclerosis: The VELOCE study[END_REF][START_REF] Kappos | Randomized trial of vaccination in fingolimod-treated patients with multiple sclerosis[END_REF]. Achiron et al. showed similar results after COVID-19 vaccination with only 22.7% of serological positivity in patients treated with ocrelizumab (10/44) and 3.8% with fingolimod (1/26) compared to 100% in patients treated with cladribine (23/23) or without DMT (32/32) [START_REF] Achiron | Humoral immune response to COVID-19 mRNA vaccine in patients with multiple sclerosis treated with highefficacy disease-modifying therapies[END_REF]. Thus, these patients could be at risk of infection with SARS-CoV-2 even after vaccination. However, only one patient, treated with ocrelizumab, was reported to have vaccine failure. This patient developed COVID-19 symptoms 19 days after receiving the second dose of Pfizer-BioNTech COVID-19 vaccine and serological assay was negative for IgG to the spike protein. This apparent low frequency of vaccine failure in patients treated with anti-CD20 mAb could be explained by preservation of a cellular response to vaccination [START_REF] Sahin | COVID-19 vaccine BNT162b1 elicits human antibody and TH1 T cell responses[END_REF].

Although the size of the population is very small and so, interpretation should be taken with caution, a time from the last infusion of anti-CD20 mAb higher than 4 months seems to play a role in the humoral response after vaccination probably linking to the beginning of B-cells repopulation which around of 6 months [START_REF] Hauser | B-cell depletion with rituximab in relapsing-remitting multiple sclerosis[END_REF]. Thus, to increase the humoral response after COVID-19 vaccination, the first dose may be delayed to up to 4 months from the last infusion of anti-CD20 mAb and the next infusion need to be potentially delayed of 1 month after the second dose. However, the risk of rebound of disease activity must be considered on a case-by-case basis.

Our study has some limitations. First, the small size of the cohort limited the power of the study, especially for a comparison between the various DMTs. Second, the comparison of humoral response after COVID-19 vaccine and COVID-19 was limited by the large variation in the delay between the onset of COVID-19 or the first dose of COVID-19 vaccine and the serology.

In conclusion, the humoral response after COVID-19 vaccination was lower in MS patients treated with S1PR modulator or anti-CD20 mAb. In France, based on previous results of humoral response after vaccination, patients treated with anti-CD20 mAb receive three doses of COVID-19 vaccine but data is needed on the effectiveness of this recommendation. Our results need to be confirmed in a larger study, such as the COV-POPART cohort (NCT04824651) evaluating immune response to COVID-19 vaccines in specific populations, including MS patients.

[ 1 .

 1 58 -28.6], 16.5 [16.3 -48.5], 1116[434 -1747] and 1272 [658 -1886], respectively, p<0.001), indicating a weaker humoral response to vaccination (Table

Acknowledgments

The authors thank Thomas Senger for his assistance in collecting data.

Competing interests

Authors have no competing interests to declare.


François Mifsud

Diane Messager

Anne-Sophie Jannot

Benoît Védie

Nadia Aissaoui Balanant

Tigran Poghosyan

Edouard Flamarion

Claire Carette

Léa Lucas-Martini

Sébastien Czernichow

Nadia Aissaoui Balanant

Claire Rives-Lange
email: claire.rives-lange@aphp.fr

Clinical diagnosis, outcomes and treatment of thiamine deficiency in a tertiary hospital

Keywords: Thiamine deficiency, Wernicke's Encephalopathy, Malnutrition, Alcohol-Related Disorders

ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

Thiamine is an important cofactor for several enzymes that are essential for energy metabolism including the Krebs cycle. It also has a critical protective role in neuronal structure and function, both in the central nervous system and in peripheral nerves. [START_REF] Frank | Thiamin in Clinical Practice[END_REF] In case of insufficient intake, decrease of intestinal absorption or increased renal excretion, clinical manifestations of thiamine deficiency can develop in only a few weeks especially in situations of high carbohydrate intake, chronic alcohol consumption, or when the metabolic demand is high. [START_REF] Sechi | Wernicke's encephalopathy: new clinical settings and recent advances in diagnosis and management[END_REF] Thiamine deficiency can rapidly lead to irreversible neurological damage, heart disease and life-threatening complications. [START_REF] Donnino | Myths and misconceptions of Wernicke's encephalopathy: what every emergency physician should know[END_REF][START_REF] Akhouri | Wernicke-Korsakoff Syndrome[END_REF] Prompt diagnosis and supplementation are thus required to limit short-and long-term consequences. However, diagnosis of thiamine deficiency is challenging and several autopsy studies suggest that it often remains undiagnosed during life. [START_REF] Harper | An international perspective on the prevalence of the Wernicke-Korsakoff syndrome[END_REF][START_REF] Harper | Clinical signs in the Wernicke-Korsakoff complex: a retrospective analysis of 131 cases diagnosed at necropsy[END_REF][START_REF] Kohnke | Don't seek, don't find: The diagnostic challenge of Wernicke's encephalopathy[END_REF] The most frequent form of acute or subacute thiamine deficiency is Wernicke's encephalopathy (WE), historically defined by a triad of gait ataxia, nystagmus or ophthalmoplegia and global confusion. However in a 1986 study, only 16% of patients with confirmed WE presented with the classical clinical triad and 19% had none of them. [START_REF] Harper | Clinical signs in the Wernicke-Korsakoff complex: a retrospective analysis of 131 cases diagnosed at necropsy[END_REF] To improve the identification of patients with WE, Caine and al. modified the classical triad to propose an operational criteria with better sensitivity and specificity [START_REF] Caine | Operational criteria for the classification of chronic alcoholics: identification of Wernicke's encephalopathy[END_REF] : this criteria require only two of the four following signs : 1-dietary deficiency or malnutrition ; 2oculomotor abnormalities ; 3-cerebellar dysfunction ; 4-either an altered mental state or mild memory impairment. As measurement of blood thiamine does not necessarily reflect the vitamin store and is not performed urgently, it is recommended to rely on clinical criteria to start treatment and then assess clinical evolution. [START_REF] Galvin | EFNS guidelines for diagnosis, therapy and prevention of Wernicke encephalopathy[END_REF] There is currently no formal evidence on the optimal administration of thiamine in patients with thiamine deficiency. Because of the frequent decreased intestinal absorption and limited biodisponibility of orally administered thiamine, it is widely recommended to use the IV route, at least during the initial phase.(9) However, there is no evidence available regarding the optimal dosage and duration of treatment.(10) A Cochrane review concluded that a dose of 200 mg per day was more effective than lower doses on the neurologic and cognitive symptoms. [START_REF] Ambrose | Thiamin treatment and working memory function of alcohol-dependent people: preliminary findings[END_REF][START_REF] Day | Thiamine for Wernicke-Korsakoff Syndrome in people at risk from alcohol abuse[END_REF] Many authors recommend higher doses of 50 to 1000 mg per injection per day, and based on the 96 min half-life of free thiamine in the blood multiple daily injections are now recommended, but their superiority has not been demonstrated to date. [START_REF] Tallaksen | Kinetics of thiamin and thiamin phosphate esters in human blood, plasma and urine after 50 mg intravenously or orally[END_REF][START_REF] Cook | B vitamin deficiency and neuropsychiatric syndromes in alcohol misuse[END_REF][START_REF] Boulanger | Wernicke encephalopathy: Guiding thiamine prescription[END_REF][START_REF] Chataway | Thiamine in Wernicke's syndrome--how much and how long?[END_REF][START_REF] Nakamura | Clinical Characteristics and Outcomes Associated With High-Dose Intravenous Thiamine Administration in Patients With Encephalopathy[END_REF] The benefit of a switch to an oral thiamine supplementation and the total duration of treatment has never been proven but it is considered good practice to continue the latter for at least several weeks, as the tolerance is generally excellent. [START_REF] Latt | Thiamine in the treatment of Wernicke encephalopathy in patients with alcohol use disorders[END_REF][START_REF] Shoaib | An Atypical Long-Term Thiamine Treatment Regimen for Wernicke Encephalopathy[END_REF] Given the difficulty of the diagnosis and the uncertainties in treatment modalities, the aim of this study was to review all cases of thiamine deficiency reported in a tertiary hospital in France over a 10 years period. The objectives were to describe the clinical presentation of cases as well as imaging results, review treatments that had been prescribed in accordance or not with available guidelines, and study the short-term outcome of these patients.

Patients and methods

This is a retrospective analysis of all cases of thiamine deficiency reported in health medical records of the Georges Pompidou European Hospital in Paris (France) between January 1st 2008 and December 31th 2018. Cases were identified by searching electronic medical charts over this period for the corresponding ICD-10 diagnosis encoded by physicians. All medical charts were then manually reviewed by an investigator to confirm diagnosis and collect data from medical history, physical examination, lab and imaging results, treatment and clinical evolution during the hospital stay. Nutritional status was determined by body mass index (kg/m 2 ) and weight loss percent criteria. The diagnosis of malnutrition was established retrospectively based on the Global Leadership Initiative on Malnutrition (GLIM) that requires at least one etiologic criterion among reduced food intake or assimilation, inflammation or disease burden, and at least one phenotypic criterion among non-volitional weight loss, low BMI and reduced muscle mass.(20) Phenotypic criteria were assessed using BMI and percent weight loss. Moderate malnutrition was defined by weight loss of 5 to 10 percents within the past 6 months or 10 to 20 percents over more than 6 months and/or BMI <20 kg/m 2 (if age <70 years) or BMI <22 kg/m 2 (if age >70). Severe malnutrition was defined by weight loss greater than 10 percents within the past 6 months or greater than 20 percents over more than 6 months and/or BMI <18.5 kg/m 2 (if age <70 years) or BMI <20 kg/m 2 (if age >70). [START_REF] Cederholm | GLIM criteria for the diagnosis of malnutrition -A consensus report from the global clinical nutrition community[END_REF] The study protocol was approved by the local ethic committee (CERAPHP.5)

Statistical analysis

The collected characteristics are reported using median, 25 th (Q1) and 75 th (Q3) percentiles for quantitative variables. For categorical variables counts and percentages are reported.

Differences between groups were tested with a Fischer's exact test for categorial variables and with the Mann-Whitney test for quantitative variables. The association between studied variables and improvement of symptoms was tested by univariate logistic regression; odds ratios and their confidence intervals were calculated to quantify their prognostic impact.

Quantitative variables were dichotomized to plot the corresponding odds ratios along with binary variables' odds ratios. The cut-off was the median value for age, number of infusions and duration of supplementation. For BMI, oral and IV doses the cut-offs were respectively ≥20 kg/m 2 and ≥1000 mg. The absence of significant association with symptoms improvement was also verified when these variables were analyzed as continuous. All statistical tests were performed in R statistical software at a 95% confidence level.( 21)

Results

The electronic search identified 86 patients with a diagnosis of thiamine deficiency encoded during the study period. In 30 patients, individual review of the medical charts found no justification for this encoding and did not confirm suspicion of thiamine deficiency. Fifty-six cases of thiamine deficiency were identified, from 8 different departments including the intensive care unit. The total number of reported cases varied from 2 to 8 per year and was stable over the study period (supplementary figure 1). All patients had at least two of the four practical criteria as defined by Caine and al for the diagnosis of WE. [START_REF] Caine | Operational criteria for the classification of chronic alcoholics: identification of Wernicke's encephalopathy[END_REF] The repartition of patients in the different hospital departments is shown in supplementary table 1.

The characteristics and reasons for hospitalization of all cases are shown in table 1. Patients were predominantly males over 50 years old. The main reason for admission was neurological symptoms, followed by general status alteration, a very unspecific symptom. One third of patients had a known chronic liver disease or cirrhosis and two thirds had abnormal liver test results at admission. Eighty-eight percent of patients had at least one comorbidity (liver, lung, heart, kidney, pancreatic, neurological or psychiatric disease). Eighty percent of patients had a history of alcohol abuse. History of bariatric surgery was found in 4 of the 11 non-alcoholic patients. Twenty five percents of patients met the GLIM criteria for malnutrition, all of them in the group of patients with history of alcohol abuse. Sixteen percents had severe malnutrition. Hypoalbuminemia was found in 73% of cases. Hyponatremia and hypokalemia were frequent at admission (25% and 40% respectively), the latter occurred more specifically in patients with alcohol abuse. The detailed symptoms of patients at admission are described in table 2. All patients had at least one neurologic or psychiatric symptom. The elements of the historical WE triad were the most frequent neurological symptoms but no patient was reported to have the three elements simultaneously. Nystagmus was reported in 36% of patients. No ocular motor palsy was reported at admission but four patients complained of diplopia. Ocular motor paresis was likely present in these patients but could have been missed because the examination was not performed by an ophthalmologist or neuro-ophtalmologist.

Eighty-four percents of patients were initially diagnosed with WE and 16% with Korsakoff syndrome. Digestive symptoms however were present in 25% of cases.

A brain MRI was performed in 54% of cases (table 3). The MRI was abnormal in 63% of these patients. The interpretation mentioned lesions typical of WE in 8 of the 30 MRIs, and typical of Korsakoff syndrome in 2 of them. One third of MRIs showed a combination of nonspecific anomalies and one third were considered normal. A brain CT was performed in 50% of cases and was normal in 75% of those patients.

Eighty-four percent of patients were treated by parenteral thiamine administration (table 4).

Thiamine supplementation was continued orally after the period of IV administration in sixtysix percent of them. The majority of patients received infusions of 1000 mg. The prescribed IV dose was higher among patients with history of alcohol abuse. The total number of infusions ranged from 1 to 40. The oral supplementation was prescribed for a median time of 19 days. The oral thiamine dose was heterogenous, predominantly of 1000 mg in patients with history of alcohol abuse and 500 mg in patients without. The duration of the hospital stay was shorter in non-alcoholic patients. At the time of discharge, partial or complete improvement of symptoms was noted in 59% of patients. The prognostic value of relevant clinical, radiological and therapeutic variables was tested by logistic regression on symptoms improvement. Odds ratios for symptoms improvement after thiamine supplementation and their confidence intervals are shown in figure 1. Apart from serum albumin below 30 g/L, none of these variables were significantly associated with a better outcome. Abnormal brain MRIs seemed associated with a lesser chance of symptoms improvement but the effect was at the limit of statistical significance.

Discussion:

We present a retrospective analysis of all reported cases of thiamine deficiency in a French tertiary hospital. All reported patients had neurological or psychiatric symptoms. As only diagnosed and electronically encoded cases were retrieved, this study does not allow to estimate the prevalence of thiamine deficiency in this population. Given that the prevalence of WE was estimated around 1% on autopsy studies [START_REF] Harper | An international perspective on the prevalence of the Wernicke-Korsakoff syndrome[END_REF][START_REF] Torvik | Wernicke's encephalopathy--prevalence and clinical spectrum[END_REF], the annual number of diagnosed cases was low in comparison with the 253659 hospital stays over the study period in this center. This suggests that thiamine deficiency remains underdiagnosed even in this tertiary care setting mainly because of insidious symptoms and poor awareness among physicians. [START_REF] Peck | Low rates of thiamine prescribing in adult patients with alcohol-related diagnoses in the emergency department[END_REF] Almost two thirds of thiamine deficiency cases were diagnosed in the internal medicine department; patients with unexplained neurological symptoms or alcohol misuse are mostly referred to this unit.

Alcohol intake significantly reduces thiamine absorption in the gut and is often associated with malnutrition. [START_REF] Thomson | Patterns of 35S-thiamine hydrochloride absorption in the malnourished alcoholic patient[END_REF] Thiamine deficiency is commonly suspected among alcohol-dependent subjects, but can also occur in non-alcoholic patients : hundreds of cases have been reported in patients with no history of alcohol use, mainly in clinical settings involving malnutrition, digestive and non-digestive cancer, bariatric surgery, gastro-intestinal diseases, hyperemesis of pregnancy, prolonged parenteral nutrition without thiamine supplementation, AIDS, bone marrow transplantation, chronic kidney disease and genetic disorder of thiamine metabolism. [START_REF] Oudman | Wernicke-Korsakoff syndrome despite no alcohol abuse: A summary of systematic reports[END_REF][START_REF] Scalzo | Wernicke-Korsakoff syndrome not related to alcohol use: a systematic review[END_REF][START_REF] Isenberg-Grzeda | Wernicke-Korsakoff syndrome in patients with cancer: a systematic review[END_REF][START_REF] Iannelli | Wernicke's encephalopathy after laparoscopic Roux-en-Y gastric bypass: a misdiagnosed complication[END_REF][START_REF] Tang | Prevalence and predictors of postoperative thiamine deficiency after vertical sleeve gastrectomy[END_REF][START_REF] Singh | Wernicke encephalopathy after obesity surgery: a systematic review[END_REF][START_REF] Chiossi | Hyperemesis gravidarum complicated by Wernicke encephalopathy: background, case report, and review of the literature[END_REF][START_REF] Butterworth | Thiamine deficiency and wernicke's encephalopathy in AIDS[END_REF][START_REF] Ihara | Wernicke's encephalopathy associated with hemodialysis: report of two cases and review of the literature[END_REF][START_REF] Oudman | Wernicke's encephalopathy in hyperemesis gravidarum: A systematic review[END_REF][START_REF] Divya | Atypical neurological manifestations in Wernicke's encephalopathy due to hyperemesis gravidarum[END_REF][START_REF] Long | Total parenteral nutrition caused Wernicke's encephalopathy accompanied by wet beriberi[END_REF][START_REF] Kono | Mutations in a thiamine-transporter gene and Wernicke's-like encephalopathy[END_REF][START_REF] Oudman | Wernicke's encephalopathy in Crohn's disease and ulcerative colitis[END_REF] The vast predominance of alcohol dependent patients in our series could suggest that thiamine deficiency is particularly underdiagnosed outside of this population. In spite of the important increase in the number of bariatric surgeries during the study period we did not find a significant increase of thiamine deficiency cases. Nonetheless 4 of the 11 cases unrelated to alcohol abuse had history of bariatric surgery, confirming the vulnerability of these patients. [START_REF] Zheng | Wernicke Encephalopathy and Sleeve Gastrectomy: A Case Report and Literature Review[END_REF] The neuropsychological manifestations of thiamine deficiency are known to be more diverse than the classic triad. [START_REF] Torvik | Wernicke's encephalopathy--prevalence and clinical spectrum[END_REF][START_REF] Ahmed | An Unusual Presentation of Catatonia in Nonalcoholic Wernicke Encephalopathy[END_REF] Although some neuro-ophtalmologic signs may have been missed by the non-specialized physicians performing the initial examination, nystagmus was found in 36% of cases. This confirms that nystagmus is one of the most frequent and early sign of thiamine deficiency. [START_REF] Dewardener | Cerebral beriberi (Wernicke's encephalopathy); review of 52 cases in a Singapore prisoner-of-war hospital[END_REF][START_REF] Victor | The Wernicke-Korsakoff syndrome. A clinical and pathological study of 245 patients, 82 with post-mortem examinations[END_REF][START_REF] Kattah | Vestibular signs of thiamine deficiency during the early phase of suspected Wernicke encephalopathy[END_REF][START_REF] Kattah | Early Signs of Thiamine Deficiency: A Case Report[END_REF][START_REF] Ikeda | Nystagmus in non-alcoholic Wernicke encephalopathy[END_REF][START_REF] Wiggli | Early recognition of thiamine deficiency: ocular motor deficits in a patient with nutritional deprivation due to persistent antibiotic-related nausea[END_REF] It is the most common ocular finding. The most frequent type is an early horizontal nystagmus, followed by the installation of a gaze-holding failure.

Position upbeat nystagmus has also been described and can convert to a permanent downbeat nystagmus. [START_REF] Kattah | Conversion of upbeat to downbeat nystagmus in Wernicke encephalopathy[END_REF][START_REF] Kattah | Vertical nystagmus in Wernicke's encephalopathy: pathogenesis and role of central processing of information from the otoliths[END_REF] Vestibular reflexes should thus be tested at the bedside in every patient with a clinical history compatible with early WE. Nystagmus is easy to detect and does not depend on the patient's ability to stand. Patients with diplopia should undergo a detailed evaluation including a cross-cover test or a red glass test to uncover a possible abducens paresis. [START_REF] Leigh | The Neurology of Eye Movements. The Neurology of Eye Movements[END_REF][START_REF] Isen | Neuro-ophthalmic Manifestations of Wernicke Encephalopathy[END_REF] Thiamine deficiency can also cause peripheral neuropathy resulting in polyneuritis, as well as non-specific memory disorders. Non-neurological consequences such as heart failure (with high-output heart failure in the classic form of the "wet Beri-Beri"), gastrointestinal manifestations, lactic acidosis or isolated coma have also been frequently reported. [START_REF] Donnino | Myths and misconceptions of Wernicke's encephalopathy: what every emergency physician should know[END_REF][START_REF] Donnino | Gastrointestinal Beriberi: A Previously Unrecognized Syndrome[END_REF] In this study the initial clinical description of cases is indeed heterogeneous and demonstrates that the diagnosis should be considered in patients admitted for non-specific reasons such as general status alteration or fall, when associated with history of alcohol abuse or malnutrition. However, it is remarkable that only 25% of cases fulfilled the GLIM criteria for malnutrition, suggesting that manifestations of thiamin deficiency can appear before significant weight loss occurs. Nevertheless, the high frequency of hypoalbuminemia attests of the severity of pre-existing diseases and their potential impact on the nutrionnal status. Indeed, a serum albumin below 30g/L at admission was associated with significantly lower chances of clinical improvement. Digestive symptoms were frequent and could be related to the numerous comorbidities or to a specific gastro-intestinal manifestation of thiamine deficiency that has been suggested by previous works. [START_REF] Donnino | Gastrointestinal Beriberi: A Previously Unrecognized Syndrome[END_REF] Vomiting or malabsorption also contribute directly to the occurrence of thiamine deficiency. Only one patient with heart failure was reported; patients with an unexplained cardiomyopathy and a poor nutritional status should however be evaluated for thiamine deficiency.( 52) Five patients presented with concomitant magnesium deficiency, which might have been implicated in the occurrence of WE. Magnesium has been reported to be an essential cofactor of thiamine into its active diphosphate and triphosphate forms.( 53) Even if thiamine blood concentration is neither necessary nor sufficient for the diagnosis, the lack of a systematic thiamine measurement before supplementation is a limitation of our study. This underlines that clinicians do not use blood thiamine measurement for the practical diagnosis in our center, probably due the long delivery time of results.

WE can also be confirmed by brain magnetic resonance imaging (MRI) : specific alterations of the thalami, mammillary bodies, tectal plate, and periaqueductal area have been described on T2 and fluid-attenuated inversion recovery (FLAIR) sequences, and are often associated with non-specific or "atypical" signal alterations of the brain, forebrain, cerebellum and corpus callosum. [START_REF] Suzuki | Acute Wernicke's encephalopathy: comparison of magnetic resonance images and autopsy findings[END_REF][START_REF] Manzo | MR Imaging Findings in Alcoholic and Nonalcoholic Acute Wernicke's Encephalopathy: A Review[END_REF][START_REF] Ota | Comprehensive review of Wernicke encephalopathy: pathophysiology, clinical symptoms and imaging findings[END_REF] Mamillary body atrophy is a relatively specific abnormality described on MRI: it has been identified in approximately 80 percent of chronic Wernicke's encephalopathy and was not founded in controls or in patients with Alzheimer disease. [START_REF] Charness | Mamillary body atrophy in Wernicke's encephalopathy: antemortem identification using magnetic resonance imaging[END_REF] Mamillary body atrophy can be detected within one week of the onset of acute WE.(58) A study comparing 15 patients with acute WE with 15 asymptomatic alcohol abusers and 15 controls reported sensitivity of brain MRI of 53% and specificity of 93% for the diagnosis of WE but the results were not compared to autopsy.( 59) Abnormal T2 signal could disappear within 2 days after treatment with thiamine. [START_REF] Park | Magnetic resonance reflects the pathological evolution of Wernicke encephalopathy[END_REF] On the contrary brain computed tomography (CT) has a low sensitivity to detect WE. In this series, brain MRI was performed in only 54% of cases in spite of its previously reported utility. Sixty-three percents of these MRIs were abnormal but only 8 showed specific anomalies allowing to formally confirm of the diagnosis.

The lack of diagnostic value of MRI in this series emphasizes the difficulty of this diagnosis.

Although brain CT was often performed, mainly to rule out an alternative diagnosis at admission, it was normal in 75% of patients. This confirms the low sensitivity of CT scan in this indication. Although at the limit of statistical significance the presence of lesions on the brain MRI was associated with a lower chance of clinical improvement after treatment.

If not rapidly treated, WE can progress to permanent damages of mamillary bodies and diencephalon causing amnesia, confabulations and dementia known as Korsakoff syndrome. [START_REF] Foster | The Wernicke-Korsakoff Syndrome and Related Neurologic Disorders Due to Alcoholism and Malnutrition. 2nd Edition[END_REF] The important heterogeneity in the treatment strategies chosen inside a single center underlines the need for more consensual and widely communicated guidelines across medical specialties. The current lack of clinical trials to validate the administration route and dosage of thiamine supplementation is the main obstacle to such a consensus. Parenteral administration leads to high cerebral concentrations due a to a passive blood-brain barrier passage and is the initial recommended route. The actual recommendations to favor high dose infusions in alcohol-dependent patients were followed in a majority of cases but the dose was more variable outside this group. The duration of the IV and oral supplementation was highly heterogenous and reflects the lack of current evidence on this matter. These observations also confirm the need for intra-hospital referrals or teams specialized in nutritional medicine, able to provide homogenous management advice across the different specialty wards. [START_REF] Peck | Low rates of thiamine prescribing in adult patients with alcohol-related diagnoses in the emergency department[END_REF] The low cost and safety of thiamine argue for widespread supplementation, along with other vitamins or magnesium replacement in alcohol abusers and others patients prone to thiamine deficiency.

The retrospective collection of clinical data was the main study's limit and prevented access to a systematic and detailed evaluation of neurological symptoms and particularly eye movements. We also lacked statistical power to identify predictors of symptoms reversibility after thiamine supplementation. As expected, patients initially diagnosed with Korsakoff rarely saw an improvement of their neurological symptoms. The administration route, duration and dose were not associated with the probability of symptoms improvement in this series, but the statistical power was limited by the small number of patients.

Conclusion

This retrospective review of thiamine deficiency cases highlights the clinical and radiological heterogeneity of this under-diagnosed but life-threatening condition. The difficulty of diagnosis should lead to starting thiamine supplementation in patients with risk factors or suggestive symptoms, especially in patients with an history of alcohol abuse, as an early supplementation may allow a regression of symptoms. Evidence-based guidelines widely spread across medical specialties are strongly needed to validate and unify the management of this medical emergency.

Figure 1 .

 1 Figure 1. Odds ratios of symptoms improvement after thiamine supplementation and 95%

Table 1 . Characteristics of cases at admission

 1

	All patients	History of alcohol abuse
	No	Yes

Table 2 . Clinical symptoms of cases noted at admission

 2

	All patients	History of alcohol abuse
		No	Yes

Table 3 . Neuroradiological investigations performed in cases

 3

	All patients	History of alcohol abuse
	No	Yes	p

Table 4 . Modalities of prescribed thiamine supplementation and outcome of cases

 4

	All patients	History of alcohol abuse
	No	Yes	p

Funding statement: this research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Conflicts of interest: the authors declare that they have no competing interests.