NEW YORK (Reuters Health) – Multiple sclerosis (MS) patients who smoke have a speedier progression of the disease, a new study in the Archives of Neurology suggests.

Dr. Alberto Ascherio of the Harvard School of Public Health in Boston and his colleagues also found that smokers with MS were more likely to have the progressive form of the disease, in which symptoms steadily get worse, rather than the relapsing-remitting form, in which a person has MS symptoms intermittently.

“Most of the adverse effects were seen for current smokers, which in some way is good news because it suggests that stopping smoking can help,” Ascherio told Reuters Health.

People who smoke are known to be at increased MS risk, but research on whether smoking affects the course of the illness has had conflicting results, he and his colleagues note. They followed 1,465 MS patients, 17.5% of whom were current smokers, for an average of just over three years to investigate.

Of the 891 patients the team followed for that period to determine the rate of progression from one form of disease to the other, 72 saw their MS progress to the worse relapsing-remitting form: 20 of 154 smokers, 20 of 237 ex-smokers, and 32 of 500 never-smokers.

That meant that the smokers were 2.4 times as likely as non-smokers to have primary progressive MS, and those who had relapsing-remitting disease were 2.5 times more likely than never-smokers to develop secondary progressive MS during the follow-up period.

At the study’s outset, the smokers had more disability, more severe disease, and more atrophy in their brains. Over time, they also showed a faster increase in the total amount of injured brain tissue and their degree of brain atrophy.

The mechanism through which cigarette smoking could worsen MS isn’t clear, Ascherio said. Smoking has been linked to some other autoimmune conditions, such as rheumatoid arthritis, he noted, but not others, so the habit’s effects on the immune system could be a factor; another possibility would be that cigarette smoke is toxic to the nervous system.

There are currently no proven risk factors for progression of MS that a patient can do anything about, Ascherio noted.

“Although causality remains to be proved,” he and his colleagues write, “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.”

SOURCE: Archives of Neurology, July 2009.