Smoking has been shown consistently to increase the risk of developing multiple sclerosis (MS) by 50%. It is not entirely clear, however, whether smoking also influences the clinical course of the disease: the few studies that addressing this issue have yielded conflicting results.
A recent study published in Brain sought to investigate the effects of smoking on disability progression and disease severity in a cohort of patients with clinically definite MS.1 The study population comprised patients registered in the MS specialist clinic database at Nottingham University Hospital in the UK, which contains greater than 98% of the identified patients with MS in the region. Patients are seen routinely and undergo medical and neurological evaluation, including estimation of Expanded Disability Status Scale (EDSS) score, with reporting of history, treatments and investigation results. Patients were asked about smoking status; if they were smokers, they were asked about the number of cigarette smoked per day at their first clinic visit. Patients were grouped as being non-smokers, ex-smokers, or current smokers. ‘Ever-smoking’ was defined based on smoking at least 20 packs of cigarettes in a lifetime, or at least 1 cigarette per day for a year.
Data were analysed from 895 patients (270 male, 625 female), with mean age 49 years and with mean disease duration of 17 years. At the time of disease onset or at diagnosis, 49% of patients were regular smokers (ever-smokers).
The risk of reaching EDSS score milestones of 4 and 6 in ever-smokers compared with never-smokers was 34% and 25% more likely, respectively. Current smokers showed 1.64 and 1.49 times higher risk of reaching EDSS Scale scores 4 and 6 than non-smokers. Ex-smokers who stopped smoking either before or after the onset of the disease had a significantly lower risk of reaching EDSS scores 4 (35% less) and 6 (31% less) than current smokers, and there was no significant difference between ex-smokers and non-smokers in terms of time to EDSS scores 4 or 6.
The data suggest that regular smoking is associated with more severe disease and faster disability progression. In addition, smoking cessation—whether before or after disease onset—is associated with slower progression of disability.
Key Points About Smoking and MS
. The evidence against smoking is mounting. It is well established that smoking increases the risk of MS (although this is not the same as saying that smoking causes MS). The evidence regarding smoking and disease progression has previously been less rigorous.
. This study demonstrates that smokers reach disease milestones more rapidly than non-smokers.
. Interestingly, people who stop smoking (even after diagnosis) appear to have slightly slower disease progression; their disease behaves more like that of a non-smoker.
. We still don’t know conclusively how smoking can influence MS risk and progression. A clearer understanding can help us further understand MS pathogenesis.
1. Manouchehrinia A, Tench CR, Maxted J, et al. Tobacco smoking and disability progression in multiple sclerosis: United Kingdom cohort study. Brain. 2013 Jun 11.