Smoking May be Linked to Rapid Progression of Multiple Sclerosis

New research suggests that patients with multiple sclerosis (MS) who smoke appear to experience a more rapid progression of their disease. Previous studies show that cigarette smokers are at higher risk of developing MS, but the effect of smoking on the progression of MS remains uncertain.

The study, led by Brian C. Healy, PhD, of Brigham and Women’s Hospital, Harvard Medical School, and Massachusetts General Hospital and colleagues, followed 1,465 patients with MS who visited a referral center between February 2006 and August 2007. Participants were an average age of 42 and had MS for an average of 9.4 years. Their progression was assessed by clinical characteristics and MRI scans over an average of 3.29 years.

A total of 780 (53.2 percent) of the patients had never smoked, 428 (29.2 percent) had smoked in the past, and 257 (17.5 percent) currently smoked. During follow-up, seven people who had never smoked began smoking and 57 current smokers quit. Current smokers had significantly more severe disease at the beginning of the study and were more likely to have primary progressive MS—characterized by steady decline—rather than relapse-remitting MS (involving alternating periods of attacks and symptom-free periods).

The authors note that an adverse effect of smoking on the progression of MS would be consistent with previous research. Components of cigarette smoke are known to have toxic effects on brain and neural tissue; for example, cyanides, which have been associated with the destruction of the myelin coating of nerve cells (a characteristic feature of MS) in animals.

"Other chemicals in smoke (e.g., nicotine) can compromise the blood-brain barrier or have immunomodulatory effects," the authors write. "Cigarette smoke increases the frequency and duration of respiratory infections, which have been linked to risk of MS and to the occurrence of MS relapses."

"In conclusion, the results of this large and in part prospective investigation support the hypothesis that cigarette smoking has an adverse effect on progression of MS as measured by clinical and MRI outcomes," the authors stated.

"Although causality remains to be proved, these findings suggest that patients with MS who quit smoking may not only reduce their risk of smoking-related diseases but also delay the progression of MS."