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To the Editor I read with interest the article by Pakpoor and colleagues1 investigating the risk for hospital admission for multiple sclerosis (MS) after admission for alcohol misuse. While interesting, the study is far from proving a causal relationship of alcohol misuse on MS risk. As likely seen in another study by the same team,2 there is an issue of reverse causality that is not remedied by excluding admissions in the same year because MS risk factors likely act many years before the clinical onset of the disease.3 Furthermore, because MS has significant psychological impact, it is likely that alcohol misuse is a result of the impact of having MS.4 Therefore, the authors should test whether there is a risk for alcohol misuse admission in patients with MS. Furthermore, it is notable that the association is seen primarily in men, suggesting that the association is a result of having MS (as documented in the literature5) rather than reflecting confounding.
Voci C. Multiple Sclerosis and Alcohol Misuse. JAMA Neurol. 2015;72(2):238. doi:10.1001/jamaneurol.2014.3876