Lifetime exposure to smoking and substance abuse may be associated with late-onset multiple sclerosis: a population-based case-control study.

Background: Late-onset multiple sclerosis (LOMS), defined as the development of MS after the age of 50, has shown a substantial surge in incidence rates and is associated with more rapid progression of disability. Besides, studies have linked tobacco smoking to a higher chance of MS progression. However, the role of smoking on the risk of developing LOMS remains unclear. This study aims to evaluate the possible association between lifetime exposure to cigarette and waterpipe smoking, drug abuse, and alcohol consumption and the risk of LOMS.

Methods: This population-based case-control study involved LOMS cases and healthy sex and age-matched controls from the general population in Tehran, Iran. The primary data for confirmed LOMS cases were obtained from the nationwide MS registry of Iran (NMSRI), while supplementary data were collected through telephone and on-site interviews. Predesigned questionnaire for multinational case-control studies of MS environmental risk factors was used to evaluate the LOMS risk factors. The study employed Likelihood ratio chi-square test to compare qualitative variables between the two groups and utilized two independent sample t-test to compare quantitative data. Adjusted odds ratio (AOR) for age along with 95% confidence intervals (CI) were calculated using matched logistic regression analysis in SPSS 23.

Results: Totally, 83 LOMS cases and 207 controls were included in the analysis. The female to male ratio in the cases was 1.5: 1. The mean ± SD age of 83 cases and 207 controls was 61.14 ± 5.38) and 61.51 ± 7.67 years, respectively. The mean ± SD expanded disability status scale (EDSS) score was 3.68 ± 2.1. Although the results of waterpipe exposure had no significant effect on LOMS development (P-value: 0.066), ever cigarette-smoked participants had a significantly higher risk of developing LOMS than those who never smoked (AOR: 2.57, 95% CI: 1.44-4.60). Furthermore, people with a history of smoking for more than 20 years had 3.45 times the odds of developing MS than non-smokers. Drug and alcohol abuse were both associated with LOMS in our study; of which opioids (AOR: 5.67, 95% CI: 2.05-15.7), wine (AOR: 3.30, 95% CI: 1.41-7.71), and beer (AOR: 3.12, 95% CI: 1.45-6.69) were found to pose the greatest risk of LOMS, respectively.

Conclusion: For the first time, we identified smoking, drug, and alcohol use as potential risk factors for LOMS development. According to the global increase in cigarette smoking and alcohol use, these findings highlight the importance of conducting interventional approaches for prevention.