Association Between Cigarette Smoking and Multiple Sclerosis: A Review.

Importance: Cigarette smoking is a common environmental exposure and addiction, which has severe health consequences. Smoking is a risk factor for multiple sclerosis (MS); also, smoking has been associated with disease activity and overall prognosis for patients with MS. Observations: Cigarette smoking is an irritative agent on the lungs, in which a proinflammatory cascade starts that culminates in autoimmunity. Inflammation may increase the risk of MS in some individuals, in a process driven by antigen cross-reactivity between lung antigens and myelin antigens. Genetics plays a central role in the individual predisposition to mounting an autoimmune reaction. Also, free radicals, cyanates, and carbon monoxide in cigarette smoke may be directly toxic to neurons. Patients with MS who smoke have higher rates of disease activity, faster rates of brain atrophy, and a greater disability burden. Some of the outcomes of smoking were found to be reversible, which makes counseling key. Conclusions and Relevance: The pathways involved in cigarette smoking should be further analyzed to understand the mechanisms whereby smoking worsens MS prognosis. The proinflammatory and neurotoxic outcomes of cigarette smoking may be shared by other environmental exposures, such as pollution and organic solvents. From a global perspective, efforts should be made to diminish the prevalence of cigarette smoking in patients with MS.