Individuals with relapsing-remitting multiple sclerosis (RRMS) who smoke and are being treated with interferon beta (IFN-β) have a higher risk for relapse compared with nonsmoking patients with RRMS, according to an observational study published in Neurology.1

Investigators analyzed the DNA of patients with RRMS from the Danish Multiple Sclerosis Biobank (N=834), all of whom were being treated with IFN-β. Patients were divided into smokers (n=242) and nonsmokers (n=592) based on questionnaire results and relapse rates obtained from the Danish Multiple Sclerosis Treatment Register were compared between the 2 groups.

There was an association between relapses and age at the start of treatment (incidence rate ratio [IRR] 0.894, 95% CI 0.824-0.971; P =.007). Specifically, a 10-year age increase was associated with a 10.6% relapse rate reduction. Compared with nonsmokers, RRMS IFN-β-treated patients had a 20% higher risk for relapse (IRR 1.20, 95% CI 1.021-1.416; P =.027).

In addition, smokers had a 27% increase in relapse rate per pack of cigarettes per day (IRR 1.27, 95% CI 1.056-1.537, P =.012). The investigators observed no associations between relapse, smoking, N-acetyltransferase-1 gene, and human leukocyte antigen.

Recall bias in the questionnaire portion of the study as well as the retrospectively reported relapses prior to IFN-β treatment represent 2 substantial study limitations. In addition, the findings are also limited in that the investigators did not differentiate between nonsmokers and occasional smokers when defining the nonsmoking study arm.

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While this study did not investigate whether smoking cessation could be helpful for reducing RRMS disease activity, the researchers believe their findings “should encourage physicians to inform patients with MS about the harmful effect of smoking and increase focus on smoking cessation.”

Reference

Petersen ER, Oturai AB, Koch-Henriksen N, et al. Smoking affects the interferon beta treatment response in multiple sclerosis [published online January 17, 2018]. Neurology. doi:10.1212/WNL.0000000000004949