Smoking Boosts Multiple Sclerosis Risk

From Medscape Medical News
Allison Gandey

September 2, 2009 — Evidence is mounting that people at risk for autoimmune disease are especially susceptible to the harmful effects of smoking, but a new study suggests that nicotine might not be the culprit.

Those who stopped smoking saw their risk decline quite quickly.
"Our study confirms that smoking cigarettes increases the risk of multiple sclerosis," lead investigator Anna Hedström, MD, from the Karolinska Institutet in Stockholm, Sweden, said during an interview. "We found that the more a person smokes, the greater the risk. But what is interesting is we found that those who stopped smoking saw their risk decline quite quickly, and some exsmokers were as healthy as people who never smoked."

But in a surprising twist, researchers found that smokeless tobacco did not increase this risk. "That's not to say it isn't bad for you," Dr. Hedström told Medscape Neurology. "Other studies have linked it to heart disease and cancer — particularly lip cancer." She suggests that carcinogens other than nicotine might be affecting the immune system.

Speaking on behalf of the Multiple Sclerosis Society of Canada, Aprile Royal, assistant vice president of clinical programs, said that "there are lots of reasons not to smoke; it is bad for anyone. But for people with multiple sclerosis or those at particular risk, smoking is especially dangerous."

She complimented the study design, in which a large sample of patients was drawn from multiple centers. The work is part of the Epidemiologic Investigation of Multiple Sclerosis — an extensive case–control study of more than 900 patients and 1800 control subjects.

Researchers report that the increased risk was apparent even among participants who had smoked moderately. They report: "We found clear evidence of a dose-response correlation between cumulative dose of smoking and the risk of developing the disease."

The increased risk for multiple sclerosis associated with cigarettes remained up to 5 years after a patient stopped smoking, but it later declined.

A study published in Neurology last month showed that people with multiple sclerosis who smoke have higher lesion volumes, more atrophy, and are at greater risk for blood–brain-barrier disruption (Neurology. 2009;73:504-510).

During a recent interview, lead author of that study, Robert Zivadinov, MD, from the University of New York School of Medicine and Biomedical Sciences in Buffalo, said: "Ours is the first study to demonstrate that smoking can promote brain-tissue injury in multiple sclerosis patients."

Autoimmune Disease and Smoking Don't Mix

The findings are similar to those of a study published in July (Arch Neurol. 2009;66:858-864). As previously reported by Medscape Neurology, investigators found that smoking contributes to rapid disease progression.

Asked for comment when the study was first published, Lily Jung, MD, from the Swedish Neuroscience Institute in Seattle, Washington, and member of the American Academy of Neurology, said that "this is just more ammunition for telling patients that to stop smoking is the easiest thing they can do to treat their multiple sclerosis."

During an interview, Dr. Hedström said she agrees. She also recommends that people with a family history of multiple sclerosis avoid smoking.

Neurology. 2009;73:696-701. Abstract