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Multiple sclerosis (MS) is a complex neurologic disease caused by both genetic and environmental risk factors. To our knowledge, few studies have investigated the relationship between alcohol and MS risk, and these have been limited by small sample sizes and inconsistent results. 1-3 Hedström and colleagues4 reported that alcohol consumption exhibits a dosedependent inverse association with MS risk. We aimed to determine whether individuals with alcohol misuse disorders, presumed to consume large quantities of alcohol, have a lower MS risk than the general population.

agnosed in a National Health Service hospital during the study period. A reference cohort was constructed by identifying people admitted for various other, mainly minor, medical and surgical conditions and injuries (Table 1, footnotes). None of the control conditions within the reference cohort, when studied separately, had unusually high or low rates of MS when compared with other conditions in the reference cohort. We then searched for any subsequent episode of daycase care or hospital admission for, or death from, MS in these cohorts. We considered that rates of MS in the reference cohort would approximate those in the general population while allowing for migration in and out of it. The standardized rate ratio was then calculated (Table 1, footnotes).

Methods | We conducted a record-linkage study using linked data sets of anonymized English Hospital Episode Statistics (records of every episode of day-case care or hospital admission in all English National Health Service hospitals) and death registrations for England from 1999 to 2011. The English National Research Ethics Service approved use of the data sets (ref 04/Q2006/176). The methods have been described fully elsewhere.5 Three cohorts of people with a record of day-case care or inpatient admission for alcohol abuse, alcohol dependence, and alcohol use (International Statistical Classification of Diseases, 10th Revision codes F10.1, F10.2, and F10.9) were constructed by identifying the first recorded episode in which each condition was di-

Results | The number of people in the reference cohort was more than 6.7 million (50% women). The number of people in the alcohol use, alcohol abuse, and alcohol dependence cohorts were 10 156 (35% women), 255 827 (29% women), and 281 305 (29% women), respectively. There was a significantly increased risk for MS following alcohol abuse, alcohol dependence, and alcohol use (Table 1). We considered the possibility of reverse causality or that the increased risk for MS may be related to the alcohol-related care itself (eg, increased surveillance). Therefore, we analyzed the data for whether the occurrence of the first record of MS was within, or after, 1 year following the first admission for each alcohol misuse disorder. There was a significantly elevated risk for MS within 1 year

RESEARCH LETTER

Alcohol Misuse Disorders and Multiple Sclerosis Risk

Table 1. Observed Number of People With Multiple Sclerosis Following Admission for Each Alcohol Misuse Disorder and Rate Ratios With 95% CIsa Observed People With Multiple Sclerosis, No.

Rate Ratio (95% CI)b

P Value

Alcohol abuse

198

1.49 (1.29-1.72)

Alcohol misuse disorders and multiple sclerosis risk.

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