PhD H Koffijberg
email: h.koffijberg@umcutrecht.nl

MD E Buskens

MD Gje Rinkel

ANEURYSM OCCLUSION IN ELDERLY PATIENTS WITH ANEURYSMAL SUBARACHNOID HEMORRHAGE: A COST-UTILITY ANALYSIS

Keywords: Subarachnoid haemorrhage, Intracranial aneurysm, Elderly, Disease Management, Cost Effectiveness

Background: Aneurysm occlusion after subarachnoid hemorrhage (SAH) aims to improve outcome by reducing the rebleeding risk. With increasing age overall prognosis decreases and the complications of aneurysm occlusion increase. The balance of risks for aneurysm occlusion in elderly SAH patients in different age categories and clinical conditions is unknown.

Methods: A Markov model was used to evaluate quality-adjusted life years (QALY), additional costs, and incremental cost-effectiveness ratios (ICER) of aneurysm occlusion in 192 patient subgroups, based on age, gender, neurological condition at admission, time since SAH, and aneurysm size and location. Probabilistic sensitivity analyses were performed.

Results: For patients admitted in poor condition ≥10 days after SAH, and patients older than 80 year, admitted in poor condition admitted ≥4 days after SAH, occlusion implied QALY loss and increased costs. Only for women younger than 79 and men younger than 74 years admitted in good condition within 4 days the ICER of occlusion fell below € 50,000 per QALY. Occlusion was beneficial and cost-saving in women aged 74 years or younger admitted in good condition within 4 days and a small posterior circulation aneurysm.

Conclusions:

Aneurysm occlusion is harmful in some subgroups of elderly patients and beneficial in others. It is cost-effective only in specific subgroups that comprise a large part of the patients encountered in clinical practice. Beyond the age of 80 years the balance between risks and benefits is often no longer positive for occlusion, and it should only be considered if the predicted life expectancy leaves margin for benefit.

INTRODUCTION

Almost half the patients with aneurysmal subarachnoid hemorrhage (SAH) die within the first months, whereas 10-20% remain dependent on help for activities of daily life. [START_REF] Hop | Case-fatality rates and functional outcome after subarachnoid hemorrhage: a systematic review[END_REF] In patients surviving the initial hours after SAH, rebleeding is an important complication. The risk is particularly high immediately after SAH, and decreases steadily over time after the first 24 hours. [START_REF] Brilstra | Effectiveness of neurosurgical clip application in patients with aneurysmal subarachnoid hemorrhage[END_REF] Untreated aneurysms have a cumulative risk of rebleeding within the first month after SAH of approximately 40%. [START_REF] Brilstra | Rebleeding, secondary ischemia, and timing of operation in patients with subarachnoid hemorrhage[END_REF] If no rebleeding occurs before day 10, the remaining risk within the first month decreases to 25%. At day 15 this risk is 15% and at day 20 only 5%. [START_REF] Brilstra | Rebleeding, secondary ischemia, and timing of operation in patients with subarachnoid hemorrhage[END_REF] Although generally SAH occurs in relatively young patients, currently 15-20% of the patients with SAH are over 70 years old. [START_REF] Braun | Treatment and outcome of aneurysmal subarachnoid haemorrhage in the elderly patient[END_REF][START_REF] Horiuchi | Surgical treatment for aneurysmal subarachnoid hemorrhage in the 8th and 9th decades of life[END_REF] Aneurysm occlusion reduces the risk of poor outcome (death or dependence). [START_REF] Brilstra | Effectiveness of neurosurgical clip application in patients with aneurysmal subarachnoid hemorrhage[END_REF] However, the evidence is limited to the typical patient population, and may not apply to the elderly. The risk of complications of aneurysm treatment increases with age, [START_REF] Brilstra | Effectiveness of neurosurgical clip application in patients with aneurysmal subarachnoid hemorrhage[END_REF][START_REF] Qureshi | Prevention and treatment of thromboembolic and ischemic complications associated with endovascular procedures: Part II--Clinical aspects and recommendations[END_REF] as does the prevalence of co-morbidity. [START_REF] Fortin | Prevalence of multimorbidity among adults seen in family practice[END_REF] For unruptured aneurysms the risk of poor outcome from preventive aneurysm occlusion can be higher than 30% for patients older than 70 years, depending on the size and site of the aneurysm. [START_REF] Wiebers | Unruptured intracranial aneurysms: natural history, clinical outcome, and risks of surgical and endovascular treatment[END_REF] In patients with SAH, the risks associated with aneurysm treatment are likely to be higher. Moreover as life expectancy decreases, aneurysm occlusion to prevent recurrent SAH in the long term loses relevance. Thus, occlusion in elderly patients probably has worse costeffectiveness compared to younger patients, and may even decrease the risk of good outcome, for example in patients in a poor clinical condition, especially if already several days have elapsed after the SAH. The (cost-) effectiveness does not depend on patient age only, but also on gender, clinical condition on admission, time since onset, type of treatment, and aneurysm site and size. We used Markov model Monte Carlo simulation to assess health effects and costs of aneurysm occlusion in elderly patients with SAH according to age, clinical condition, days since onset, and site and size of the aneurysm. [START_REF] Sonnenberg | Markov models in medical decision making: a practical guide[END_REF][START_REF] Hunink | Decision Making in Health and Medicine: Integrating Evidence and Values[END_REF]

METHODS

Model structure

A Markov model was developed to reflect patients over 70 years of age admitted to the hospital with SAH, using data from the literature. Supportive medical treatment only was compared with aneurysm occlusion (i.e. coiling as preferred treatment and clipping if coiling is not feasible). Figure 1 Federation of Neurological Surgeons Scale grade IV-V, or Hunt and Kosnik Scale grade IV-V. Poor outcome was defined as modified Rankin Scale grade 4-5, or Glasgow Outcome Scale grade 2-3. In all outcome health states, except dead, a distinction was made between the first month after the SAH, the second to eighteenth month after the SAH, and subsequent months. In the first month a patient is at high risk of rebleeding and may be treated with aneurysm occlusion or not. Patients may be admitted early after onset of SAH, but also later due to patient or doctor delay. Since treatment effects decrease with time lapsed, and the risk of treatment varies over time, different time frames were considered.

Patients eligible for treatment <4 days were assumed to be treated the day after admission. Patients eligible for treatment between days 4-10 were assumed to be treated on day 10, whereas patients eligible ≥10 days after SAH were assumed to be treated the day after treatment became viable.

Rebleeding may be fatal, or cause neurological deterioration (i.e. patients may move from good to poor health states). We assumed conservatively managed patients may rebleed during the entire first month, whereas patients with occluded aneurysms can rebleed only up to occlusion. After the first month treatment is assumed to have ended.

In the second to eighteenth month after SAH, patients may die from unrelated causes, experience recurrent SAH, or recover (i.e. they may move from poor to good health states). Patients in poor health states were assumed to have a high age-dependent risk of dying from unrelated causes. Patients in good health states were assumed to be healthy but still experiencing excess mortality compared with the general population. [START_REF] Ronkainen | Evidence for excess long-term mortality after treated subarachnoid hemorrhage[END_REF] After eighteen months patients may still die from unrelated causes, or have recurrent SAH. Recovery from the initial SAH, however, was no longer considered possible.

Model parameters

Table 1 shows the model parameters. The utilities in Table 1 were derived from the literature, and are allocated to the similarly named health states depicted in Figure 1. The costs of aneurysm coiling and clipping from Table 1 are event costs associated with treatment options at the start of subtree (D) in Figure 1. Note that the cost of medical management is incurred for both healthy and disabled patients in the conservative treatment strategy, which is not shown in Figure 1. Moreover, regardless of treatment strategy the annual costs of a nursing home are accounted for in patients remaining in a disabled state. The cost associated with death is incurred once for each patient at the time of death. For both treatment strategies, recurrent SAH may occur from 18 months onwards after the initial episode of SAH, in both healthy and disabled patients. A cost equal to the cost of conservative treatment is assumed. Transition probabilities and relative effects dependent on subgroup characteristics are shown in Table 2. Briefly, beta distributions were used for binomial data and Dirichlet distributions for multinomial data whenever possible, i.e. when event counts and non-event counts were available. In case actual (count) data were not available uniform distributions were used, with ranges based on expert opinion. Finally, triangular distributions were used for recalculated estimates from systematic review studies, and in case the range of uncertainty was not completely contained in the interval [0, 1].

Only actual medical costs were taken into account. Age and gender-specific mortality risks were used to model survival unrelated to SAH. P(recurrent SAH per year) after coiling, year 1 0.026 0.017-0.038 Beta [START_REF] Molyneux | International subarachnoid aneurysm trial (ISAT) of neurosurgical clipping versus endovascular coiling in 2143 patients with ruptured intracranial aneurysms: a randomised comparison of effects on survival, dependency, seizures, rebleeding, subgroups, and aneurysm occlusion[END_REF] P(recurrent SAH per year) after coiling, year 2+ 0.002 0.001-0.005 Beta [START_REF] Molyneux | International subarachnoid aneurysm trial (ISAT) of neurosurgical clipping versus endovascular coiling in 2143 patients with ruptured intracranial aneurysms: a randomised comparison of effects on survival, dependency, seizures, rebleeding, subgroups, and aneurysm occlusion[END_REF] P(recurrent SAH per year) after clipping, year 1 0.010 0.005-0.018 Beta [START_REF] Molyneux | International subarachnoid aneurysm trial (ISAT) of neurosurgical clipping versus endovascular coiling in 2143 patients with ruptured intracranial aneurysms: a randomised comparison of effects on survival, dependency, seizures, rebleeding, subgroups, and aneurysm occlusion[END_REF] P(recurrent SAH per year) after clipping, year 2+ 0.0006 0.00008-0.0024 Beta [START_REF] Molyneux | International subarachnoid aneurysm trial (ISAT) of neurosurgical clipping versus endovascular coiling in 2143 patients with ruptured intracranial aneurysms: a randomised comparison of effects on survival, dependency, seizures, rebleeding, subgroups, and aneurysm occlusion[END_REF] P(recurrent SAH per year) after cons. tr., year 1 0.113 0.09-0.139 Beta [START_REF] Locksley | Report on the cooperative study of intracranial aneurysms and subarachnoid hemorrhage. Section V. 2. Natural history of subarachnoid hemorrhage, intracranial aneurysms and arteriovenous malformations[END_REF] P(recurrent SAH per year) after cons.tr., year 2+ 0.142 0.106-0.185 Beta [START_REF] Locksley | Report on the cooperative study of intracranial aneurysms and subarachnoid hemorrhage. Section V. 2. Natural history of subarachnoid hemorrhage, intracranial aneurysms and arteriovenous malformations[END_REF] P(poor outcome) due to coiling complications 0.033 0.009-0.083 Beta [START_REF] Sedat | Endovascular treatment of ruptured intracranial aneurysms in patients aged 65 years and older: follow-up of 52 patients after 1 year[END_REF], [START_REF] Lubicz | Endovascular treatment of ruptured intracranial aneurysms in elderly people[END_REF], † P(death) due to coiling complications 0.025 0.005-0.071 Beta [START_REF] Sedat | Endovascular treatment of ruptured intracranial aneurysms in patients aged 65 years and older: follow-up of 52 patients after 1 year[END_REF], [START_REF] Lubicz | Endovascular treatment of ruptured intracranial aneurysms in elderly people[END_REF], †

Costs in Euros

Discounting

Cost discount per year 4% ---Benefits (effects) discount per year 4% ---* Values are recalculated from the referenced studies. P (X) denotes the probability of the event X occurring. † Data from these two studies were combined in order to get a more robust estimate. The probability of the outcomes poor and death for conservative treatment were set to the respective probabilities of these outcomes for coiling with the risk of perioperative complications resulting in poor outcome or death subtracted. ‡ Costs are updated to 2005 with Dutch inflation indices, and converted to Euros (€1 = $1.27; December 2007) # Cost of treatment is assumed to include costs due to possible rebleeding before or during the treatment. § Costs were obtained by summing up the medical and hospital stay components of the cost of aneurysm coiling. % Recurrent SAH is assumed to be treated conservatively (due to the expected age and condition at recurrence). $ Estimates of the utility of patients after major stroke vary widely, [START_REF] Post | The utility of health states after stroke: a systematic review of the literature[END_REF] thus a large range was used. Relative effect on cost of treatment, 0.85 0.70-1.00 Uniform Good [START_REF] Elliott | Predicting length of hospital stay and cost by aneurysm grade on admission[END_REF] based on length-of-stay hospital data 1.15 1.00-1.30 Uniform Poor [START_REF] Elliott | Predicting length of hospital stay and cost by aneurysm grade on admission[END_REF] * Values are recalculated from the referenced studies. P (X) denotes the probability of the event X occurring. †

We assumed a 10% uncertainty in the estimates, standard analyses resulted in just 1% uncertainty as 43,510 patients were assessed in the reference study (with 10% age categories overlap slightly). ‡ Probability is zero by definition: A rebleeding may cause a degradation of health condition (e.g. from good condition to poor condition), but never an improvement.

#

Unpublished data obtained from Swedish registries [START_REF] Koffijberg | Subarachnoid haemorrhage in Sweden 1987-2002: regional incidence and case fatality rates[END_REF]. This is the standardized mortality ratio (SMR) for patients in good clinical condition after treatment, compared with the general population. §

The relative effect calculated from the referenced study, containing patients in poor clinical condition, was also applied to patients in good clinical condition.

%

Here favourable outcome is defined as 'good clinical condition', unfavourable is defined as 'poor clinical condition' or 'dead'.

Model assumptions

The complication rate of clipping was assumed to depend on patient age. [START_REF] Horiuchi | Surgical treatment for aneurysmal subarachnoid hemorrhage in the 8th and 9th decades of life[END_REF] However, this was not assumed for the less invasive coiling procedure. The likelihood of recovery from the initial SAH was assumed to be equal for the treatment modalities. Patients with recurrent SAH were assumed to always be treated conservatively due to advanced age and presumed very poor condition after subsequent SAH. As the model focused on elderly patients eligible for occlusion, it was assumed that in the occlusion strategy all patients would be coiled or clipped. The model did not account for costs of follow-up after occlusion. It was assumed that follow up angiograms would not be performed in elderly patients. Severe complications (rebleeding, treatment complications or recurrent SAH) occurring in patients in poor health states were presumed to be fatal. Likewise, patients in good health states experiencing complications were assumed to (temporarily) move to poor health states. The utility of patients in poor health states was set equal to the health-related quality of life of survivors of a major stroke. Furthermore, these patients were assumed to move to nursing homes after hospital discharge.

Model simulation

The Markov model was constructed using TreeAge (2009, TreeAge Software, Williamstown, MA). For each subgroup a Monte Carlo simulation was performed comprising 1,000 hypothetical cohorts of 10,000 elderly patients. The clinical course of the patients over time was evaluated.

Model outcomes

For each subgroup the expected number of patients with one or more recurrent haemorrhages, expected costs and quality-adjusted life expectancy (QALE) were calculated. Also, the management outcome of patients at discharge, one month after SAH, was determined (i.e. the health state occupied by patients). The expected incremental costs and health benefits, and incremental cost-effectiveness ratios (ICER) for occlusion were calculated for each subgroup. In addition, cost-effectiveness acceptability curves (CEAC) were constructed. [START_REF] Van Hout | Costs, effects and C/E-ratios alongside a clinical trial[END_REF] Our base group consisted of 70-74 year old women admitted in good clinical condition <4 days after SAH, with an anterior aneurysm <10mm. This group represents the largest proportion of elderly with SAH, and may expect the highest benefit from occlusion. Probabilistic sensitivity analyses were performed. [START_REF] Briggs | Handling uncertainty in cost-effectiveness models[END_REF]35] Also, the effects of a 1.5% discount rate instead of 4%, and a doubled mortality risk were assessed.

RESULTS

Table 3 shows the expected outcomes per strategy. The number of patients with good outcome at one month increased rapidly with time since onset for the conservative treatment strategy, but not for the occlusion strategy. The QALEs in Table 3 reflect the balance between the (remaining) risk of rebleeding, the risk of treatment complications, and the risk of recurrent SAH, i.e., summarize the overall health benefits.

Figure 2 shows a nomogram with the absolute change in QALE for the occlusion strategy. Occlusion did not provide health benefits in patients admitted in poor condition ≥10 days after SAH. It provided minimal or no health benefits in patients older than 80 years admitted in poor condition ≥4 days after SAH. For most other subgroups of elderly, occlusion resulted in health benefits.

In Figure 3 the uncertainty with respect to the .incremental costs and effects of aneurysm occlusion compared with conservative treatment is shown. This is the uncertainty in model outcomes that is due to parameter uncertainty caused by sampling values for the model parameters for which distributions were defined in Tables 1 and2. Figure 3 indicates that there is relatively little uncertainty with respect to the difference in health effects: the incremental health effect is positive for all subgroups of men and women shown, except for men or women admitted in poor condition > 10 days after SAH where it is clearly negative. Furthermore, for all subgroups of men the incremental costs are highly likely to be positive. For women incremental costs are likely to be positive for women admitted in poor condition < 4 days after SAH and women admitted in good condition > 10 days after SAH. Incremental costs for women admitted in good condition < 4 days after SAH may be positive or negative, as well as the incremental costs for women admitted in poor condition > 10 days after SAH.

Figure 4 shows the estimated health gains and additional costs of occlusion, for selected subgroups. It is apparent that incremental costs are larger for patients admitted in poor condition than for patients admitted in good condition. Incremental costs are similar for men and women, whereas incremental effects are higher for women and in patients admitted <4 days.

Applying a willingness-to-pay threshold of € 50,000/QALY the probability that aneurysm occlusion is costeffective varied from 0% to 90%. Thus, occlusion is likely to be cost-effective only in some subgroups of elderly. The estimated ICER of occlusion fell below € 50,000/QALY only for women aged 70-79 year, and men aged 70-74 years admitted in good condition <4 days.

In all subgroups except in women aged 70-74 years, admitted in good condition <4 days after onset, with a small posterior aneurysm, occlusion was more costly than conservative treatment. In this subgroup occlusion saved € 1,409 and resulted in 0.36 QALY gain, i.e. the occlusion strategy dominated the conservative strategy.

Figure 5 presents cost-effectiveness acceptability curves for subgroups in which occlusion may be costeffective. For all other subgroups it appeared unlikely that occlusion will ever become cost-effective.

Cost-effectiveness of occlusion was slightly worse in patients with large aneurysms than in patients with small aneurysms, and slightly better when the aneurysm is located in the posterior circulation compared with the anterior circulation (not shown).

In our base group the preferred treatment would be aneurysm occlusion, resulting in 0.29 QALY gain, at an additional cost of € 72 (ICER € 247/QALY). Probabilistic sensitivity analysis in this subgroup demonstrated results were sensitive to the parameter relating treatment costs to clinical condition of the patient, for both strategies. Also, results for conservative treatment were sensitive to the probability of poor or good outcome after rebleed and to risk of recurrent SAH after conservative treatment. Results for occlusion were sensitive to the probability of poor or good outcome after coiling.

With a 1.5% discount rate for costs and effects instead of 4% the ICER of occlusion in the base group improved from € 247 to € 118/QALY. Doubling the mortality rate due other causes, e.g. due to additional cardiovascular events, resulted in a worse ICER (€ 26054/QALY).

DISCUSSION

Occlusion of ruptured intracranial aneurysms instead of conservative treatment improves outcome only in some subgroups of elderly patients. Moreover, even if the outcome is (slightly) improved the costs may be prohibitive. Therefore, no single optimal strategy for all elderly patients with SAH exists.

In patients admitted in poor condition and >10 days after SAH occlusion will even decrease the QALE. From our nomogram it is apparent that the health benefits provided by occlusion decrease with patient age and with time elapsed after SAH onset (Figure 2). In addition, these health benefits are lower for men than for women, are lower for small compared to large aneurysms, and are lower for aneurysms in the posterior rather than the anterior circulation. The particular nomogram format chosen facilitates rapid inspection in clinical practice of the estimated health benefits of occlusion, given the specific characteristics of an individual patient and the ruptured aneurysm. In subgroups of patients in which occlusion results in health benefits, the cost-effectiveness varied considerably and depended foremost on the clinical condition of the patient and time elapsed since onset of SAH. In addition, cost-effectiveness decreased with increasing age and was worse for men than for women. Occlusion was cost-effective in women aged 70-79 years, and men aged 70-74 years, admitted in good condition <4 days after SAH. Although the limited data available in the literature on elderly patients with SAH resulted in uncertainty surrounding estimates of cost-effectiveness, this uncertainty has little impact on our conclusions. The ICER of occlusion was less than € 50,000/QALY for only 7 of the 192 subgroups of elderly. However, these subgroups consist of the youngest elderly, admitted to the hospital early, and therefore contain the most patients.

Our study provides new insight for indications where as yet no randomized controlled trial has been conducted, and very likely never will be. For many elderly conservative treatment appears to be the preferred option. Our model-based findings are in fact quite similar to evidence obtained in an actual RCT in patients with abdominal aorta aneurysms (AAA). [START_REF]Endovascular aneurysm repair and outcome in patients unfit for open repair of abdominal aortic aneurysm (EVAR trial 2): randomised controlled trial[END_REF] Our study has certain limitations. Firstly, we could not include in the model all patient and aneurysm characteristics (risk factors) that may affect the risk of rebleeding, treatment outcome, and the risk of recurrent SAH. Accurate estimates of the effect of characteristics such as smoking, hypertension and aneurysm shape, are not available from the literature. Therefore, our model provides estimates for 'average' values of these characteristics.

Secondly, co-morbidities and disease histories were not explicitly accounted for. Elderly patients may already have a reduced life expectancy (e.g. due to a cardiovascular event preceding the SAH). In the model patients surviving SAH in good condition experience only excess mortality due to SAH. Thus, the predicted health benefits of occlusion are probably overestimated.

Thirdly, we did not include uncertainty regarding the cost estimates used in our model, due to lack of detailed data on these costs. Consequently, the already considerable uncertainty in our model results

still is an underestimation of the total uncertainty.

Finally, the assumptions underlying our analysis may have influenced our results. Most notably, the assumption that no angio or MRA follow-up would be performed after coiling will result in overly optimistic cost-effectiveness estimates for the occlusion strategy when in actual practice follow-up would be performed. Similarly, the assumption that recurrent SAH in patients in poor health states will be fatal, and in patients in good health states will cause them to (temporarily) move to poor health states, may also lead to overly optimistic cost-effectiveness estimates for the occlusion strategy when in fact the consequences of recurrent SAH might be less severe, e.g. due to improved medical care.

A low risk of perioperative complication of occlusion was used, and a high risk of recurrent SAH following the index SAH (Table 1). Actual perioperative complication risks in elderly patients may be higher (e.g. the mortality risk from coiling may be 5%) [START_REF] Cai | Endovascular treatment of intracranial aneurysms in the elderly: single-center experience in 63 consecutive patients[END_REF] and the risk of recurrent SAH may be lower (e.g. 3.5% per year) [START_REF] Winn | The long-term prognosis in untreated cerebral aneurysms: I. The incidence of late hemorrhage in cerebral aneurysm: a 10-year evaluation of 364 patients[END_REF]. Consequently, health benefits may again be overestimated.

With an ageing population the number of elderly patients with SAH increases. How to provide optimal treatment to these patients is a multi-facetted problem. Studies concluding that age alone should not preclude aneurysm treatment often performed coiling or clipping in all (treatable) elderly patients with SAH. [START_REF] Braun | Treatment and outcome of aneurysmal subarachnoid haemorrhage in the elderly patient[END_REF][START_REF] Horiuchi | Surgical treatment for aneurysmal subarachnoid hemorrhage in the 8th and 9th decades of life[END_REF] However, the favourable outcomes found in some patients with occluded aneurysms were never compared directly with outcomes of patients in a condition suitable for occlusion but offered conservative treatment. Since a very poor clinical condition of patients is a major reason for not performing aneurysm treatment, the fatality and morbidity rates reported for these patients are high indeed. This may simply be explained by the poor prognosis from the outset, and not from withholding aneurysm treatment.

From our direct (model-based) comparison of no aneurysm treatment and occlusion we conclude that occlusion is harmful in some subgroups of patients and beneficial in others. It is cost-effective only in specific subgroups that comprise a large part of the patients encountered in clinical practice. Beyond the age of 80 years the balance between risks and benefits is often no longer positive for occlusion, and it should only be viewed as option in patients with a prolonged life expectancy. A final important finding is that if aneurysm occlusion is considered, it should be done as soon as possible, because postponing will render occlusion ineffective and inefficient. Table 3. The expected number of patients (95% CI) surviving the first month after treatment, in poor condition and good condition, in a hypothetical cohort of 10,000 women with SAH from an anterior aneurysm <10mm. Also, the expected number of patients with recurrent SAH and the estimated QALE per patient are shown.

  depicts the occlusion strategy. Outcomes were assessed for 5 year age categories (70-74, 75-79, 80-84, 85+), gender, neurological condition at admission (poor-grade or good-grade), day of treatment since onset (<4, 4-10, 11-21), aneurysm size (<10 or ≥10 mm) and aneurysm location (anterior or posterior). Ultimately, outcomes in terms of costs (Euros, € 1 = $1.20 as of November 2008) and effects (qualityadjusted life-years (QALYs)) were estimated for 192 subgroups. The model used time cycles of one month and a lifetime horizon. Two entry health states were defined through which patients enter the model: good or poor clinical condition at admission. Three outcome health states were distinguished for the conservative treatment strategy: good or poor clinical condition, and dead. The aneurysm occlusion strategy comprised five outcome health states: good or poor clinical condition after coiling, good or poor clinical condition after clipping, and dead. Separate health states for coiled and clipped patients were required, as these treatments imply different risks of recurrent SAH. Poor clinical condition on admission was defined as Hunt and Hess Scale IV-V, World

Figure 1 .

 1 Figure 1. Illustration of the aneurysm occlusion strategy part of the Markov model. Copies of the subtrees (A)-(D) are used at several locations in the model.

Figure 2 .

 2 Figure 2. Nomogram of the expected effect of aneurysm occlusion, in months of changes to the quality-adjusted life expectancy of patients.

Figure 3 .

 3 Figure 3. The cost-effectiveness plane showing the uncertainty in incremental costs and effects of aneurysm occlusion for selected subgroups of elderly men [A] and women [B]. All subgroups concern 70-74 years old patients with ruptured aneurysms <10mm of the anterior circulation.

Figure 4 .

 4 Figure 4. The cost-effectiveness of aneurysm occlusion for selected subgroups of elderly men [A] and women [B]. Subgroups differ with respect to age category, day of admission, and clinical status at admission. All subgroups concern patients with ruptured aneurysms <10mm of the anterior circulation.Lines connect the age categories 70-74,75-79,80-84, and 85+ years. In general, the health gain due to occlusion decreases with age, therefore age increases along the lines, from the right to the left.

Figure 5 .

 5 Figure 5. Cost-effectiveness acceptability curves for all subgroups of elderly men [A], and women[B], in which the probability that occlusion was cost-effective, compared with conservative treatment, exceeded 20% for a willingness-to-pay of € 100,000/QALY.

TABLE 1 .

 1

	Model parameter	Value *	Range	Distribution	Source
	Probabilities
	P(recovery to good state in month 1-18 after SAH) 0.281	0.121-0.494	Beta	[12]

TABLE 2 . Model parameters dependent on subgroup characteristics

 2

		Value *	Range	Distri-	Age	Gender	Day	Clinical	Aneurysm	Aneurysm	Source
				bution			adm.	state	size	location
	Probabilities
	P(aneurysm coiling is possible)	0.729	0.609-0.828	Beta						Anterior	[24]
		0.950	0.751-0.999	Beta						Posterior	[24]
	P(death in nursing home per year),	0.222	0.200-0.244	Uniform 70-74	Female					[25], †
		0.265	0.238-0.291	Uniform 75-79						[25], †
		0.315	0.284-0.347	Uniform 80-84						[25], †
		0.447	0.403-0.492	Uniform 85+						[25], †
	P(death in nursing home per year),	0.264	0.237-0.290	Uniform 70-74	Male					[25], †
		0.314	0.283-0.346	Uniform 75-79						[25], †
		0.374	0.337-0.412	Uniform 80-84						[25], †
		0.531	0.478-0.584	Uniform 85+						[25], †
	P(death after rebleeding before treatment)	0.558	0.407-0.754 Dirichlet 1				Good			[26]
		0.882	0.726-0.967 Dirichlet 2				Poor			[26]
	P(poor outcome after rebleeding before trm.)	0.294	0.151-0.475 Dirichlet 1				Good			[26]
		0.133	0.039-0.307 Dirichlet 2				Poor			[26]
	P(good outcome after rebleeding before	0.118	0.033-0.275 Dirichlet 1				Good			[26]
	treatment)	0	-	-				Poor			‡
	P(favourable outcome) after aneurysm	0.639	0.585-0.691	Beta	70-79			Good			[5]
	clipping)%
		0.235	0.162-0.322	Beta	70-79			Poor			[5]
		0.606	0.483-0.720	Beta	80+			Good			[5]
		0.111	0.014-0.347	Beta	80+			Poor			[5]
	P(unfavourable outcome after clipping is poor 0.389	0.173-0.643	Beta				Good			[27]
	clinical condition and not death)	0.107	0.023-0.282	Beta				Poor			[27]

TABLE 2 .

 2 CONTINUED

	Model parameters dependent on	Value *	Range	Distri-	Age	Gend	Day	Clinical	Aneurysm	Aneurysm	Source.
	subgroup characteristics			bution		er	adm.	state	size	location
	Probabilities
	P(death) after coiling	0.043	0.022-0.074	Dirichlet 3				Good			[28]
		0.121	0.034-0.282	Dirichlet 4				Poor			[28]
	P(poor outcome) after coiling	0.104	0.071-0.145	Dirichlet 3				Good			[28]
		0.394	0.229-0.579	Dirichlet 4				Poor			[28]
	P(rebleeding before treatment)	0.089	0.058-0.129	Beta			< 4		< 10 mm		[29]
		0.192	0.109-0.301	Beta			< 4		≥ 10 mm		[29]
		0.24	0.192-0.288	Uniform			4-10				[3],&
		0.41	0.328-0.492	Uniform			> 10				[3],&
	Relative effects on model parameters
	Standardized mortality ratio death other	1.565	1.422-1.751	Beta	70-79						#
	causes
		1.282	1.186-1.418	Beta	80+						#
	RR of good outcome after aneurysm	1	-	-					< 10 mm		[30], §
	occlusion
		0.592	0.200-1.389	Triangular					≥ 10 mm		[30], §

TABLE 3 .

 3

	Gender			Poor outcome at 1 month	Good outcome at 1 month	Patients with recurrent SAH	Quality-adjusted life expectancy
	Age	Clinical Day of
	cat.	cond.	adm.	Conservative	Occlusion	Conservative	Occlusion	Conservative	Occlusion	Conservative	Occlusion
	Men
	70-74	Poor	< 4	2,877 (1,910-3,970) 3,039 (1,697-4,610) 3,266 (2,093-4,413)	4,108 (2,663-5,833)	474 (343-610)	117 (63-187)	0.46 (0.33-0.58)	0.56 (0.45-0.70)
	years		4-10	3,240 (2,063-4,503) 2,994 (1,687-4,540) 3,833 (2,757-5,027)	3,939 (2,520-5,670)	538 (357-720)	115 (57-190)	0.52 (0.41-0.65)	0.54 (0.43-0.66)
			> 10	3,547 (1,980-5,023) 3,019 (1,510-4,573) 4,607 (3,343-6,317)	4,147 (2,673-5,887)	640 (473-823)	118 (73-180)	0.60 (0.47-0.75)	0.56 (0.44-0.68)
		Good	< 4	1,694 (1,157-2,287) 1,152 (660-1,807)	5,984 (5,083-6,930)	7,819 (6,370-9,283)	594 (433-770)	135 (83-197)	0.67 (0.56-0.78)	0.83 (0.74-0.93)
			4-10	1,468 (1,017-2,033) 1,120 (637-1,723)	6,901 (5,967-7,650)	7,630 (6,027-9,283)	639 (493-800)	130 (80-197)	0.74 (0.63-0.84)	0.82 (0.73-0.90)
			> 10	1,178 (827-1,580)	1,146 (680-1,723)	7,895 (7,297-8,357)	7,840 (6,370-9,313)	693 (540-863)	132 (80-207)	0.81 (0.73-0.90)	0.83 (0.75-0.93)
	80-84	Poor	< 4	2,954 (2,053-3,920) 3,108 (1,843-4,513) 3,255 (2,270-4,657)	3,736 (2,270-5,720)	319 (210-423)	73 (33-120)	0.23 (0.16-0.30)	0.26 (0.19-0.33)
	years		4-10	3,212 (2,157-4,537) 2,977 (1,643-4,720) 3,848 (2,463-5,280)	3,661 (2,197-5,323)	356 (240-470)	73 (37-113)	0.27 (0.18-0.34)	0.26 (0.18-0.33)
			>

Table legends Table 1 .

 legends1 Value, range, and distribution for model parameters independent of the subgroup under consideration.

Table 2 .

 2 Value, range, and distribution for model parameters that depend on the subgroup under consideration.

&The uncertainty in these estimates was not given or estimable directly. Therefore, a 20% degree of uncertainty was assumed and a uniform distribution was used. Dirichlet i Parameters denoted by d(i) follow a combined Dirichlet distribution, i.e. the uncertainty in the combined parameter set is evaluated simultaneously.

FUNDING

This study was funded by the Netherlands Heart Foundation (# 2006B082).

EXCLUSIVE LICENSE

The Corresponding Author has the right to grant on behalf of all authors and does grant on behalf of all authors, an exclusive licence (or non-exclusive for government employees) on a worldwide basis to the BMJ Publishing Group Ltd and its Licensees to permit this article (if accepted) to be published in Journal of Neurology, Neurosurgery & Psychiatry and any other BMJPGL products to exploit all subsidiary rights, as set out in our licence (http://jnnp.bmj.com/ifora/licence.pdf).

CONFLICTS OF INTEREST

The authors have no conflicts of interest to disclose.


Bednařík Josef

Sládková Dagmar

Kadaňka Zdeněk

Dušek Ladislav

Keřkovský Miloš

Voháňka Stanislav

Novotný Oldřich

Urbánek Igor

Němec Martin

MD Josef Bednařík

ARE SUBJECTS WITH SPONDYLOTIC CERVICAL CORD ENCROACHMENT AT INCREASED RISK OF CERVICAL SPINAL CORD INJURY AFTER MINOR TRAUMA?

Keywords: cervical spondylosis, spinal cord compression, myelopathy, trauma Word count: 1658

Introduction

Degenerative changes in the cervical spine are part of the normal aging process and are almost omnipresent in older people [START_REF] Matsumoto | MRI of cervical intervertebral discs in asymptomatic subjects[END_REF]. They may lead to the development of clinical symptoms in some individuals if the discs and/or osteophytes impinge on neural structures such as the nerve root or spinal cord. Spondylotic cervical cord encroachment (SCCE) detected by imaging methods, mostly MRI, is a prerequisite for the clinical diagnosis of cervical spondylotic myelopathy (CSM). However, SCCE can also be asymptomatic with regard to myelopathy [START_REF] Matsumoto | MRI of cervical intervertebral discs in asymptomatic subjects[END_REF][START_REF] Teresi | Asymptomatic degenerative disk disease and spondylosis of the cervical spine: MR imaging[END_REF]. CSM develops insidiously, but it has been reported to occur after trauma [START_REF] Foo | Spinal cord injury in forty-four patients with cervical spondylosis[END_REF][START_REF] Hughes | Spinal-cord damage from hyperextension injury in cervical spondylosis[END_REF][START_REF] Regenbogen | Cervical spinal cord injuries in patients with cervical spondylosis[END_REF][START_REF] Katoh | Influence of minor trauma to the neck on the neurological outcome in patients with ossification of the posterior longitudinal ligament (OPLL) of the cervical spine[END_REF]. Some authors have suggested that individuals who have asymptomatic spondylotic cervical cord encroachment (ASCCE) on the cervical spinal cord are at increased risk of acute myelopathy if they experience minor trauma [START_REF] Emery | Cervical spondylotic myelopathy: diagnosis and treatment[END_REF][START_REF] Shedid | Cervical spondylosis anatomy: pathophysiology and biomechanics[END_REF]. This has led some surgeons to recommend decompression surgery for the purpose of preventing this trauma-induced myelopathy in individuals presumed susceptible [START_REF] Epstein | Laminectomy for cervical myelopathy[END_REF][START_REF] Lauryssen | Severe cervical stenosis: Operative treatment of continued conservative care?[END_REF] and this topic became a matter of controversy [START_REF] Murphy | Cervical spondylosis with spinal cord encroachment: should preventive surgery be recommended?[END_REF].

The aim of our study was retrospectively to analyse all traumas of the cervical spine in our cohort of 199 individuals with ASCCE followed for the median period of 44 months, and investigate any relationship to clinical manifestation of myelopathy and type of cervical spinal cord compression.

Methods

Group

The study sample consisted of a cohort of 199 subjects (94 women and 105 men; median age 51 years, range 28-82 years) recruited consecutively between January 1993 and January 2005 and followed up to July 2007, who completed at least a 2-year follow-up. MRI examination of the cervical spine and spinal cord was performed in all patients who exhibited clinical signs and symptoms of cervical radiculopathy or moderate to severe chronic or intermittent axial cervical pain. All included patients had to meet the following inclusion criteria: MR signs of spondylogenic or discogenic compression of the cervical spinal cord with or without concomitant change in signal intensity from the cervical cord on T2/T1 images (see reference 12 for further details).

Axial pain or clinical signs and/or symptoms of radiculopathy that could be controlled by conservative treatment.

Absence of any current clinical signs and symptoms that could be possibly attributed to cervical cord involvement.

During the follow-up period (median 44 months) progression in symptomatic myelopathy was found in 45 patients (22.6%); the 25 th percentile time to clinically-manifested myelopathy was 48.4 months.

Further details of the clinical, imaging and electrophysiological evaluation and algorithm of the study that centred upon risk factors predicting clinical manifestation of myelopathy have been published elsewhere [START_REF] Bednarik | Presymptomatic spondylotic cervical myelopathy -an updated predictive model[END_REF]. The presence of any trauma, both before inclusion of a patient into the study and during the follow-up period, was detected with a questionnaire administered at the end of the follow-up period, and focused on:

Date and mechanism of trauma Short term sequelae (incl. loss of consciousness, fracture, weakness of extremities, disturbance of sensitivity or sphincters, therapy incl. surgery) Long-term sequelae (incl. disturbances of gait, loss of self-support, permanent disability, chronic pain.

Further, the patient case histories and a database containing complete relevant data on all patients included into the study were retrospectively analysed with respect to the occurrence and characteristics of any trauma. All traumatic episodes were subsequently classified as possibly relevant or irrelevant to cervical spinal cord injury. The following traumatic episodes were classified as possibly relevant: Traumatic episodes before the beginning of the follow-up period were correlated with the type of spinal cord compression (discogenic versus osteophytic) classified from MRI and CT scans, while traumatic episodes during the follow-up period were correlated with clinical manifestation of spondylotic cervical myelopathy.

Statistics: Univariate logistic regression models predicting probability of CSM were used for trauma as a potential risk factor, and the odds ratio was estimated with 95% confidence limits.

Results

During the follow-up period, 14 relevant traumatic events were recorded. None of them was of serious degree with fracture of the cervical spine and/or followed by immediate neurological deficit after the trauma. In terms of mechanism, there were 6 falls (all from height <6 meters), 4 sports injuries, 3 traffic accidents and one occupational injury. Among 45 patients (22.6%) who developed symptomatic myelopathy during the follow-up period, potentially relevant traumatic episodes were found in 3 patients: in two cases myelopathy became symptomatic 6 months before trauma and in one case manifestation developed 4 years after the trauma. There was no statistically significant association between traumatic events and subsequent development of symptomatic myelopathy (odds ratio [OR] 0.935; 95% confidence interval [CI]: 0.247 -3.535; p = 0.921).

We found 56 potentially relevant traumatic episodes before the beginning of the followup with possible relationships to the cervical disc herniation. In terms of mechanisms, 21 were falls (2 from height >6 meters), 12 sports injuries, 11 traffic accidents, 11 occupational injuries and 1 injury caused by a falling object.

The type of cervical spinal cord compression (herniation, osteophytes or both) was evaluated and classified as discogenic (due to disc herniation) in 50 patients (25.1%), osseous (due to osteophytes) in 67 patients (33.7%) and mixed (herniation + osteophytes) in 82 patients (41.2%) [START_REF] Bednarik | Presymptomatic spondylotic cervical myelopathy -an updated predictive model[END_REF]. We found no statistical association between traumatic events and discogenic (OR: 1.281; 95% CI: 0.636 -2.582; p = 0.484) or mixed type of compression (OR 1.767; 95% CI 0.879 -3.549, p = 0.106).

Discussion

In a cohort of 199 patients with ASCCE who progressed into symptomatic myelopathy we detected only 3 traumas of the cervical spine in those who became symptomatic, but without direct chronological relationship. Furthermore, traumatic events before detection of cervical spinal cord encroachment showed no impact on the type of spinal cord compression.

Increased risk of cervical spinal cord injury in patients with ASCCE presumed sufficient to justify preventive surgical decompression is based on case reports, case series or retrospective cross-sectional studies [START_REF] Emery | Cervical spondylotic myelopathy: diagnosis and treatment[END_REF][START_REF] Shedid | Cervical spondylosis anatomy: pathophysiology and biomechanics[END_REF][START_REF] Epstein | Laminectomy for cervical myelopathy[END_REF][START_REF] Lauryssen | Severe cervical stenosis: Operative treatment of continued conservative care?[END_REF]. Moreover, risks involved in surgery to the cervical spine in asymptomatic spinal cord encroachment have not been reported [START_REF] Murphy | Cervical spondylosis with spinal cord encroachment: should preventive surgery be recommended?[END_REF].

Some authors have reported increased risk of spinal cord injury in patients with cervical spondylosis. Regenbogen, et al [START_REF] Regenbogen | Cervical spinal cord injuries in patients with cervical spondylosis[END_REF], in a group 88 retrospectively analysed patients over the age of 40 with spinal cord injury resulting from trauma, found 25 cases with no bony or ligamentous injury but with signs of severe spondylosis as compared to 35 younger spinal cord injury patients (below 37 years of age) who showed severe bony or ligamentous injury in all but one case. Kang et al. [START_REF] Kang | Sagittal measurements of the cervical spine in subaxial fractures and dislocations. An analysis of two hundred and eighty-eight patients with and without neurological deficits[END_REF], in a retrospective analysis of 288 spinal injury patients, found significantly lower sagittal diameter of the spinal canal and Pavlov canal/body ratio at both compressed and uncompressed levels in patients with complete and incomplete spinal injury compared to those with no nerve or spinal cord injury. Yoo, et al [START_REF] Yoo | Spinal cord injury in cervical spinal stenosis by minor trauma[END_REF], among a series of 200 cases with cervical spondylosis or ossification of posterior longitudinal ligament, and symptomatic myelopathy, detected retrospectively minor trauma of the cervical spine in 63 cases, and deterioration of preexisting myelopathy or development of new myelopathy in 31 of them. Most of these cases (25) had narrow spinal canal (diameter < 10 mm).

Murphy et al. [START_REF] Murphy | Cervical spondylosis with spinal cord encroachment: should preventive surgery be recommended?[END_REF] addressed the question of whether patients with ASCCE are at increased risk of spinal cord injury after minor trauma and may thus warrant early decompression. They found none of the case-control or prospective cohort studies that are essential to drawing the firm conclusion that risk of spinal cord injury from minor trauma is increased in ASCCE.

Lauryssen et al. [START_REF] Lauryssen | Severe cervical stenosis: Operative treatment of continued conservative care?[END_REF], combining data from several databases, estimated the "worst case scenario" risk of myelopathy in the ASCCE population at 1:2100. This low risk estimate is largely consistent with our own findings.

Furthermore, Murphy et al. found no relevant study reporting the outcome of surgery in asymptomatic patients with cervical cord spondylotic encroachment [START_REF] Murphy | Cervical spondylosis with spinal cord encroachment: should preventive surgery be recommended?[END_REF]. The reported frequency of serious complications or mortality in surgical series of patients with symptomatic CSM is generally well above 1%. As reported postsurgical complications generally relate to the surgery itself rather than to myelopathy, it is not likely that the complication rate would be substantially different in asymptomatic individuals as compared to symptomatic patients.

The major limitation of our study was its retrospective design, which could have had an influence on the exact timing of trauma in some individuals. However, significant traumatic episodes were found in only 3 cases with symptomatic myelopathy and the timing of their traumas correlated with records found in their case histories. The low frequency of traumas in our cohort may have resulted, at least in part, from our recommendation to all patients with diagnosed ASCCE that they avoid risky activities, such as certain sports (skiing, climbing etc.), walking on slippery surfaces, and so on.

As we detected no severe trauma of the cervical spine in our cohort, we were not able to assess the hypothesis that stenosis of the cervical spinal canal (both degenerative and congenital) could worsen neurological sequelae of such a trauma.

We also investigated the possibility that disc herniation as a cause of spinal cord compression might more frequently be the result of preceding trauma, but found no such association.

In conclusion, the risk of spinal cord injury after minor cervical spine trauma in patients with asymptomptomatic spondylotic cervical cord encroachment appeared to be low in our cohort provided risky activities in these individuals are restricted. Implementation of preventive surgical decompression surgery into clinical practice in these individuals should be postponed until better designed studies show justification for giving it precedence over the conservative approach.

The Corresponding Author has the right to grant on behalf of all authors and does grant on behalf of all authors, an exclusive licence (or non-exclusive for government employees) on a worldwide basis to the BMJ Publishing Group Ltd and its Licensees to


MD Pantelis P Pavlakis

Haralampos Alexopoulos

MD Michael L Kosmidis

MD Eleftherios Stamboulis

MD John G Routsias

PhD Socrates J Tzartos

MD Athanasios G Tzioufas

MD Haralampos M Moutsopoulos

Professor Marinos C Dalakas
email: m.dalakas@imperial.ac.uk

Haralampos Alexopoulos Dphil

Peripheral neuropathies in Sjögren's syndrome: a new reappraisal

Keywords: Sjögren's syndrome, peripheral neuropathy, polyneuropathy, autoantibodies

come

INTRODUCTION

Sjögren's syndrome is a systemic autoimmune disease that affects 0,5 to 1% of the general population. [START_REF] Mavragani | The management of Sjogren's syndrome[END_REF][START_REF] Fox | Current issues in the diagnosis and treatment of Sjogren's syndrome[END_REF] It usually presents as an isolated glandular disease affecting exocrine glands, typically manifested with xerostomia and xerophthalmia.

Extraglandular manifestations are due to involvement of virtually every organ including the musculoskeletal system, skin, kidneys, lungs, liver and the central or peripheral nervous system (PNS). [START_REF] Mavragani | The management of Sjogren's syndrome[END_REF][START_REF] Fox | Sjogren's syndrome[END_REF] The most serious complication of Sjögren's syndrome is lymphoma, which affects 3 -6% of patients and is 44 times more frequent than in the general population. [START_REF] Kassan | Increased risk of lymphoma in sicca syndrome[END_REF][START_REF] Voulgarelis | Malignant lymphoma in primary Sjogren's syndrome: a multicenter, retrospective, clinical study by the European Concerted Action on Sjogren's Syndrome[END_REF] The clinical spectrum of peripheral neuropathies encountered in Sjögren's syndrome patients is wide [START_REF] Andonopoulos | The spectrum of neurological involvement in Sjogren's syndrome[END_REF][START_REF] Delalande | Neurologic manifestations in primary Sjogren syndrome: a study of 82 patients[END_REF][START_REF] Grant | Peripheral neuropathy associated with sicca complex[END_REF][START_REF] Mori | The wide spectrum of clinical manifestations in Sjogren's syndrome-associated neuropathy[END_REF], with sensory neuropathies being the most common. [START_REF] Grant | Peripheral neuropathy associated with sicca complex[END_REF][START_REF] Mori | The wide spectrum of clinical manifestations in Sjogren's syndrome-associated neuropathy[END_REF] The sensory neuropathies are of three distinct sub-types: distal (length-dependent) affecting sensory fibers with electrodiagnostic features of axonal involvement; painful, due to small-fiber involvement [START_REF] Chai | Painful small-fiber neuropathy in Sjogren syndrome[END_REF][START_REF] Goransson | Intraepidermal nerve fiber densities in chronic inflammatory autoimmune diseases[END_REF][START_REF] Denislic | Small nerve fibre dysfunction in a patient with Sjogren's syndrome. Neurophysiological and morphological confirmation[END_REF][START_REF] Goransson | Peripheral neuropathy in primary sjogren syndrome: a population-based study[END_REF][START_REF] Gorson | Non-length dependent small fibre neuropathy/ganglionopathy[END_REF]; and sensory ataxic, a disabling neuropathy involving the dorsal root ganglia (ganglionopathy) [START_REF] Malinow | Subacute sensory neuronopathy secondary to dorsal root ganglionitis in primary Sjogren's syndrome[END_REF][START_REF] Griffin | Ataxic sensory neuropathy and dorsal root ganglionitis associated with Sjogren's syndrome[END_REF] resulting in deafferentation [START_REF] Dalakas | Chronic idiopathic ataxic neuropathy[END_REF]. Axonal sensorimotor polyneuropathy, cranial neuropathy, multiple mononeuropathy, demyelinating polyradiculoneuropathy and autonomic neuropathy are other less frequently encountered types. [START_REF] Grant | Peripheral neuropathy associated with sicca complex[END_REF][START_REF] Mori | The wide spectrum of clinical manifestations in Sjogren's syndrome-associated neuropathy[END_REF] Although several studies have focused on the peripheral nerve manifestations of Sjögren's syndrome, two issues remain contentious; the prevalence of peripheral neuropathy, with a reported range between 2-60%, [START_REF] Andonopoulos | The spectrum of neurological involvement in Sjogren's syndrome[END_REF][START_REF] Goransson | Peripheral neuropathy in primary sjogren syndrome: a population-based study[END_REF][START_REF] Vrethem | Neuropathy and myopathy in primary Sjogren's syndrome: neurophysiological, immunological and muscle biopsy results[END_REF][START_REF] Gemignani | Peripheral neuropathy associated with primary Sjogren's syndrome[END_REF][START_REF] Govoni | Neurological involvement in primary Sjogren's syndrome: clinical and instrumental evaluation in a cohort of Italian patients[END_REF][START_REF] Harboe | Neuropsychiatric syndromes in patients with systemic lupus erythematosus and primary Sjogren syndrome: a comparative populationbased study[END_REF][START_REF] Ramos-Casals | Primary Sjogren syndrome in Spain: clinical and immunologic expression in 1010 patients[END_REF][START_REF] Skopouli | Clinical evolution, and morbidity and mortality of primary Sjogren's syndrome[END_REF][START_REF] Barendregt | Involvement of the peripheral nervous system in primary Sjogren's syndrome[END_REF][START_REF] Andonopoulos | Neurologic involvement in primary Sjogren's syndrome: a preliminary report[END_REF][START_REF] Lopate | Peripheral neuropathy in an outpatient cohort of patients with Sjogren's syndrome[END_REF][START_REF] Lafitte | Neurological complications of primary Sjogren's syndrome[END_REF][START_REF] Mauch | Neurological and neuropsychiatric dysfunction in primary Sjogren's syndrome[END_REF][START_REF] Binder | Sjogren's syndrome: a study of its neurological complications[END_REF], and the stage of the disease in which peripheral neuropathy is most commonly manifested. Some studies claim that peripheral neuropathy is a late event, presenting in patients with manifestations of severe systemic disease such as palpable purpura, low C4 complement factor, mixed monoclonal cryoglobulinaemia, glomerulonephritis and increased risk of lymphoma development. [START_REF] Skopouli | Clinical evolution, and morbidity and mortality of primary Sjogren's syndrome[END_REF] Other studies however, suggest that peripheral neuropathy is the presenting feature of an isolated glandular disease that has a benign course. [START_REF] Grant | Peripheral neuropathy associated with sicca complex[END_REF][START_REF] Mori | The wide spectrum of clinical manifestations in Sjogren's syndrome-associated neuropathy[END_REF] The pathogenesis of these neuropathies is also poorly investigated. Because Sjögren's syndrome is a systemic autoimmune disease engulfing many autoimmune processes, correlating the temporal profile and clinical patterns of the neuropathy with the type of Sjögren's syndrome's manifestations will help us understand the pathogenesis for each neuropathy subtype. Our study was therefore designed to assess the frequency of neuropathy diagnosed by means of objective clinical signs and abnormal electrophysiology, in the various stages of the disease. We also sought to examine whether the neuropathy is immune-mediated by searching for antibodies against a variety of peripheral nerve tissue antigens and for antibodies against muscarinic and ganglionic acetylcholine receptors, which have been implicated in both, Sjögren's syndrome and in various peripheral neuropathies. [START_REF] Mckeon | Ganglionic acetylcholine receptor autoantibody: oncological, neurological, and serological accompaniments[END_REF][START_REF] Vernino | Autoantibodies to ganglionic acetylcholine receptors in autoimmune autonomic neuropathies[END_REF]

PATIENTS AND METHODS

Patients

Clinical information was retrospectively obtained from the records of patients who met the diagnostic criteria of primary Sjögren's syndrome, according to the Revised European-American diagnostic criteria. [START_REF] Vitali | Classification criteria for Sjogren's syndrome: a revised version of the European criteria proposed by the American-European Consensus Group[END_REF] These patients had been followed from 1992 to 2009 at the Pathophysiology Clinic of the University of Athens Medical School,, that serves as a national referral center for systemic autoimmune diseases. All patients with previously recorded manifestations indicative of peripheral neuropathy (after providing written informed consent) were invited to participate in the current study that took place from 2008 to 2010. These patients were re-examined by a certified neurologist (MLK).

Sensory examination was based on assessing pinprick, light touch, position and vibratory sensation. Patients with objective clinical signs of neuropathy underwent electromyography and nerve conduction studies of the sural, peroneal, and median nerve (ES). Normal values, defined as the mean plus or minus 2 standard deviations, were determined from 100 normal individuals from different age groups. Skin temperature was measured to be greater than 32 o C when all electrophysiologic studies were conducted.

The cut-off was amplitude of the sural SNAP was 10μV for ages younger than 65and 8μV for ages 65 to 75 ; for people older than 85 the sural nerve amplitude was considered abnormal only when it was not elicited. The mean normal sural conduction velocity was determined at 48m/s. Peroneal CMAP amplitude cut-off was 4mV and conduction velocity 46m/s. Median nerve SNAP was 20μV and sensory conduction velocity (from digit to wrist) was 47m/s. Median nerve CMAP was 5mv and conduction velocity 50m/s. MRI or CT of the brain and/or spine were performed on a case by case basis to exclude spinal or cranial abnormalities as a possible cause for the clinical manifestations. New patients diagnosed during the study period, were also included.

Patients with other causes of peripheral neuropathy were excluded. Serum samples were obtained from all peripheral neuropathy patients and stored at -20 o C for immunological studies (see below). The study was approved by the University of Athens' Medical School Ethics Committee.

Anti-neural antibody screening

We searched for anti-neural antibodies in eight patients with clinically and electrophysiologically confirmed neuropathy, from eight controls with Sjögren's syndrome without neurologic involvement and from eight healthy controls using indirect immunofluorescence and Western blot on a variety of nerve tissues. As positive controls we used sera with known reactivities to brain and nerve antigens, namely Aquaporin-4, and MAG. Primate cerebellum and sciatic nerve sections were obtained from Euroimmun (Nerve Mosaic, No 1111-1003-2 Euroimmun, Lübeck, Germany). Human dorsal root ganglia were obtained from the Netherlands Brain Bank (Netherlands Institute for Neuroscience, Amsterdam) and sectioned in a Leica cryostat. Briefly, sections were fixed in 4% paraformaldehyde and incubated with 1% CHAPS. After blocking with 10% goat serum, they were incubated with the patients' sera diluted 1:100 in 1% goat serum followed by AlexaFluor 488 goat anti-human IgG or IgM (Invitrogen, Carlsbad, CA) diluted 1:250 in 1% goat serum. Western blot experiments were carried out as previously described, [START_REF] Murata | Antiganglion neuron antibodies correlate with neuropathy in Sjogren's syndrome[END_REF] with the only modification being the use of the AEC peroxidase substrate kit (Vector laboratories, Burlingame, CA) for development.

Anti-M1 and M3 receptor antibodies

Peptides corresponding to the second extracellular loop of M1 muscarinic acetylcholine receptor (165-185) and M3 muscarinic receptor in dimer form (213-237) were synthesised (Biosynthesis, Lewisville, TX) and ELISA experiments were carried out as previously described, [START_REF] Naito | Muscarinic acetylcholine receptor autoantibodies in patients with Sjogren's syndrome[END_REF] with the only modification being that a control well corresponding to each sample was coated only with blocking solution. The optical density (OD) of the control well was subtracted from each sample's OD. Samples were deemed positive for anti-muscarinic antibodies when the final OD was greater than the mean plus three standard deviations of normal samples tested in the same manner.

Ganglionic acetylcholine receptor antibody radioimmunoprecipitation assay.

Solubilised membrane fractions from IMR32 cells [START_REF] Vernino | Autoantibodies to ganglionic acetylcholine receptors in autoimmune autonomic neuropathies[END_REF] were labeled with 125 I-epibatidine and incubated with 5μl of patient's serum overnight at 4 o C in duplicates. Following incubation for 2 hours with goat anti-human IgG (RSR Ltd, Cardiff, UK) and precipitation, the pellets were washed with 0,5% Triton-X 100 in phosphate buffer and radioactivity was measured. The value 10 arbitrary Units was defined as the mean counts per minute value of healthy controls and samples with values greater than 25 Units were deemed positive. mAb 198 which binds to muscle acetylcholine receptor alpha-1 subunit and cross-reacts with the ganglionic alpha-3 subunit was used as positive control.

RESULTS

Patients

The records of 509 patients with primary Sjögren's syndrome were reviewed. [START_REF] Vitali | Classification criteria for Sjogren's syndrome: a revised version of the European criteria proposed by the American-European Consensus Group[END_REF]. Fourty four patients were recorded as having neuropathic symptoms or signs including paraesthesias, pain, gait unsteadiness, Romberg sign, superficial or deep sensory deficits, diminished deep tendon reflexes or muscle weakness. Two of the 44 patients were excluded from further analysis because they were found to have secondary Sjögren's syndrome or did not meet the criteria for Sjögren's syndrome Of the remaining 42 patients, originally recorded as having neuropathic symptomps , 11 were excluded from further analysis because their symptomps were caused by various musculoskeletal problems; two others with a history of trigeminal neuralgia, were asymptomatic and were also excluded. Among the remaining 29 patients, three had clinical and electrodiagnostic findings of carpal tunnel syndrome; one other was diagnosed with motor neuron disease and another with spinal stenosis. Among the remaining 24 patients, 15 complained for neuropathic symptoms such as pain and paraesthesias but the clinical and electrophysiological evaluation were normal. These patients are suspected of having a small fiber neuropathy, but they did not undergo quantitative sensory testing or skin biopsy. Accordingly, only nine patients from the initial cohort of 509 patients (1,8%) fulfilled the clinical and electrophysiological criteria of polyneuropathy; five of them were diagnosed with sensory and four with sensorimotor polyneuropathy (Table 1).

These patients with bona fide neuropathy were female, with a mean age of 65 years (range 54-84 years) at the time of the last evaluation. All complained of distal paraesthesias and had distal (length-dependent) neurological findings in the lower limbs; the upper limbs were affected only in two. In the majority of patients (6/9) the neurological findings were symmetrical. Among the patients with sensory polyneuropathy, two had position and vibratory sensation deficits, two had pinprick and light touch sensory deficits and one had sensory deficits in all tested modalities; the patients with sensorimotor polyneuropathy had mostly light touch and pinprick sensory deficits. Deep tendon reflexes were diminished or absent in eight of the nine patients.

The neuropathy was mild and all patients were ambulatory; only one needed a cane for ambulation. All patients had the electrophysiological pattern of axonal dysfunction. One patient with sensory polyneuropathy developed an acute mononeuropathy, in the setting of generalised vasculitis, confirmed by intestinal biopsy. (see Table 1 for a detailed description of the patients).

In six of nine patients, the neuropathy was a late event in the course of the disease with a median of six years (range of 2 to 24) from the time of the initial diagnosis of Sjögren's syndrome; in one the neuropathy was the presenting manifestation of Sjögren's syndrome, confirmed soon therafter; and in the rest two the neuropathy was present at the time of Sjögren's syndrome diagnosis, but the temporal relationship between the two could not be ascertained. One of the latter three patients had no extraglandular manifestations; this is in contrast to the other two who had prominent extraglandular manifestations as described below.

The majority of patients with neuropathy had active systemic disease. Extraglandular manifestations were present in seven of nine and included palpable purpura in five patients, Raynaud phenomenon in four, arthralgias in three, biopsy-documented vasculitis (in organs other than the nerves) in three, arthritis in two and lymphadenopathy in two.

Glomerulonephritis and atrophic gastritis were present in two others. Six patients (three with sensory and three with sensorimotor polyneuropathy) were classified as type I Sjögren's syndrome, which confers higher risk for lymphoma development. [START_REF] Ioannidis | Long-term risk of mortality and lymphoproliferative disease and predictive classification of primary Sjogren's syndrome[END_REF] Type I Sjögren's syndrome is defined based on the presence of at least two of the following manifestations: parotid enlargement, low C4 complement factor at the time of Sjögren's syndrome diagnosis, or palpable purpura. [START_REF] Ioannidis | Long-term risk of mortality and lymphoproliferative disease and predictive classification of primary Sjogren's syndrome[END_REF] All patients with peripheral neuropathy had antinuclear antibodies; eight had anti-Ro antibodies and two had anti-La antibodies. Rheumatoid factor was found in five. Three patients had cryoglobulinaemia. Low C4 complement factor at the time of Sjögren's syndrome diagnosis was found in 5 patients.

Table 1 (see supplemental file)

Anti-neural antibody screening

Immunofluorescence and Western blot Eight of nine polyneuropathy patients were screened for the presence of anti-neural antibodies with immunofluorescence and Western Blot.

Brain and dorsal root ganglion immunofluorescence. No consistent IgG or IgM

immunostaining pattern on neuronal structures was observed with the patient's sera, with the exception of occasional antinuclear staining, as expected.

Peripheral nerve immunofluorescence. Staining primate nerve using an IgG and IgM secondary antibodies, yielded no specific staining.

Western Blot experiments of mouse brain extracts probed with patients and healthy control sera, also revealed no specific bands.

Screening for putative peripheral neuropathy biomarkers

Muscarinic receptor autoantibodies

ELISA for anti-M1 muscarinic receptor autoantibodies We tested eight polyneuropathy patients, 33 Sjögren's syndrome patients without neurologic involvement and 20 healthy controls. Antibodies against M1 muscarinic acetylcholine receptor were not found in any of the polyneuropathy patients or healthy controls. Four of 33 Sjögren controls were positive for anti-M1 muscarinic receptor antibodies (Figure 1).

ELISA for anti-M3 muscarinic receptor autoantibodies . One of eight polyneuropathy patients was positive for antibodies against M3, as was one of 31 Sjögren's syndrome patients without neurological involvement. None of the 20 healthy controls was positive (Figure 2). This patient was diagnosed as having axonal sensorimotor polyneuropathy. Ganglionic (α3) acetylcholine receptor autoantibodies. None of the eight polyneuropathy patients and none of the four healthy controls was tested positive for ganglionic acetylcholine receptor antibodies (Figure 3).

DISCUSSION

The study found a surprisingly low (1,8%) prevalence of polyneuropathy, diagnosed by means of objective signs and abnormal electrophysiology, among a large number of patients with bona fide Sjögren's syndrome This is in contrast to previous studies which have shown a much higher prevalence ranging from 2% to 60%. [START_REF] Andonopoulos | The spectrum of neurological involvement in Sjogren's syndrome[END_REF][START_REF] Goransson | Peripheral neuropathy in primary sjogren syndrome: a population-based study[END_REF][START_REF] Vrethem | Neuropathy and myopathy in primary Sjogren's syndrome: neurophysiological, immunological and muscle biopsy results[END_REF][START_REF] Gemignani | Peripheral neuropathy associated with primary Sjogren's syndrome[END_REF][START_REF] Govoni | Neurological involvement in primary Sjogren's syndrome: clinical and instrumental evaluation in a cohort of Italian patients[END_REF][START_REF] Harboe | Neuropsychiatric syndromes in patients with systemic lupus erythematosus and primary Sjogren syndrome: a comparative populationbased study[END_REF][START_REF] Ramos-Casals | Primary Sjogren syndrome in Spain: clinical and immunologic expression in 1010 patients[END_REF][START_REF] Skopouli | Clinical evolution, and morbidity and mortality of primary Sjogren's syndrome[END_REF][START_REF] Barendregt | Involvement of the peripheral nervous system in primary Sjogren's syndrome[END_REF][START_REF] Andonopoulos | Neurologic involvement in primary Sjogren's syndrome: a preliminary report[END_REF][START_REF] Lopate | Peripheral neuropathy in an outpatient cohort of patients with Sjogren's syndrome[END_REF][START_REF] Lafitte | Neurological complications of primary Sjogren's syndrome[END_REF][START_REF] Mauch | Neurological and neuropsychiatric dysfunction in primary Sjogren's syndrome[END_REF][START_REF] Binder | Sjogren's syndrome: a study of its neurological complications[END_REF] Such a wide discrepancy can be explained on several factors. First, most of the other studies were published during the time when the diagnostic criteria for Sjögren's syndrome were still evolving and the diagnosis was at times questionable. Second, many studies have been retrospective and included contemporaneous neurological or electrophysiological assessments in a relatively small number of patients. Third, the definition of neuropathic symptoms varied greatly between series and the electrophysiological parameters, especially among patients with sensory polyneuropathy, were quite variable. Fourth, the screen samples of pSS patients were generally small. Our study has attempted to address these issues by assessing peripheral neurological involvement in the largest ever cohort of primary Sjögren's syndrome patients, while applying the latest criteria for diagnosis.

Although its retrospective design is a limitation, the study was strengthened by reevaluating all the patients with previously recorded neuropathic symptoms clinically and electrophysiologically. Further, on account of objectivity, we relied more on electrodiagnostic techniques rather than patient history or neurologic examination alone.

One notable finding was the absence of ataxic neuropathy from our study cohort. This may be linked to a referral bias as most of such cases are referred directly to neurologists or are misdiagnosed as ataxias related to other causes. Another interesting finding was the types of neuropathy; we noted an equal frequency of sensory (n=5) and sensorimotor (n=4) polyneuropathy patterns. Sensory polyneuropathy has, according to previous series, been considered a frequent manifestation compared to sensorimotor polyneuropathy. [START_REF] Grant | Peripheral neuropathy associated with sicca complex[END_REF][START_REF] Mori | The wide spectrum of clinical manifestations in Sjogren's syndrome-associated neuropathy[END_REF] The highly subjective nature of sensory examination or the lack of consensus on the diagnosis may account for some of these discrepancies. Although we found a low frequency of polyneuropathy among Sjögren's syndrome patients, a much greater number of patients presented with painful neuropathic symptoms had normal clinical and electrophysiological evaluation. It is highly likely that these patients suffer from small fiber sensory neuropathy, which has been also observed but never systematically studied in Sjögren's syndrome. [START_REF] Chai | Painful small-fiber neuropathy in Sjogren syndrome[END_REF][START_REF] Goransson | Intraepidermal nerve fiber densities in chronic inflammatory autoimmune diseases[END_REF][START_REF] Denislic | Small nerve fibre dysfunction in a patient with Sjogren's syndrome. Neurophysiological and morphological confirmation[END_REF][START_REF] Goransson | Peripheral neuropathy in primary sjogren syndrome: a population-based study[END_REF][START_REF] Gorson | Non-length dependent small fibre neuropathy/ganglionopathy[END_REF] As this appears to be the commonest pattern, the prevalence of small fiber neuropathy among Sjögren's syndrome patients merits further investigation.

The timing of the manifestation of peripheral neuropathy during the course of Sjögren's syndrome has also been debated. [START_REF] Delalande | Neurologic manifestations in primary Sjogren syndrome: a study of 82 patients[END_REF][START_REF] Grant | Peripheral neuropathy associated with sicca complex[END_REF][START_REF] Mori | The wide spectrum of clinical manifestations in Sjogren's syndrome-associated neuropathy[END_REF][START_REF] Skopouli | Clinical evolution, and morbidity and mortality of primary Sjogren's syndrome[END_REF] In the majority of our patients (6/9), peripheral neuropathy was a late event. Studies suggesting the contrary may reflect the referral pattern, as such patients are referred first to neurologists. The majority of our patients with polyneuropathy, had active, systemic Sjögren's syndrome, especially Type I Sjögren's, a subset prone to developing lymphoma. [START_REF] Ioannidis | Long-term risk of mortality and lymphoproliferative disease and predictive classification of primary Sjogren's syndrome[END_REF] Alhough none of them had a lymphoproliferative disorder at the time of evaluation, the majority of them had risk factors, such as low C4 complement factor, parotid gland enlargement, and purpura.

Whether those factors are responsible for the neuropathy remains unclear. Because Sjögren's syndrome is a systemic autoimmune disease, we hypothesised that the neuropathy may have an autoimmune pathogenesis. Because ganglionic acetylcholine receptor autoantibodies have been recently found in a variety of peripheral neuropathies, [START_REF] Mckeon | Ganglionic acetylcholine receptor autoantibody: oncological, neurological, and serological accompaniments[END_REF][START_REF] Vernino | Autoantibodies to ganglionic acetylcholine receptors in autoimmune autonomic neuropathies[END_REF] and muscarinic acetylcholine receptor antibodies have been found in patients with primary Sjögren's syndrome, [START_REF] Dawson | Antimuscarinic antibodies in Sjogren's syndrome: where are we, and where are we going?[END_REF] we screened our neuropathy patients for these autoantibodies as candidate biomarkers. No immunoreactivity was however noted. Alas, no evidence of anti-neural tissue autoimmunity was observed based on our immunofluorescence and Western Blot screening. It is likely that examination of tissues

Figure 1 .

 1 Figure 1. Anti-M1 muscarinic antibodies ELISA

Figure 2 .Figure 3 .

 23 Figure 2. 1 patient with Sjögren's syndrome and peripheral neuropathy (PN) was tested

such as nerve biopsies might have been more informative to exclude or confirm the autoimmune pathogenesis. Such studies are in process in our ongoing prospective study.

Competing interests

The authors report no competing interests