Multiple sclerosis patients who smoke seem to decline faster, a new study in the Archives of Neurology suggests.
The study also noticed 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.
The good news is that quitting smoking may delay the progression of MS in patients, the study authors say.
It's already known that smokers are at higher risk of developing MS. But the effect of smoking on the progress of MS has remained uncertain.
So Brian C. Healy of Brigham and Women's Hospital and Harvard Medical School assembled a team who studied 1,465 patients who had MS, including some who were current smokers, others who were previous smokers and some who had never smoked.
The progression of the patients' disease was assessed for just over three years both by tracking symptoms and with MRI imaging.
At the study's outset, the smokers had more disability, more severe disease, and more atrophy in their brains.
Of the 891 patients who stayed in the study, 72 saw their MS progress to the worse disease form: 20 of 154 smokers, 20 of 237 ex-smokers, and 32 of 500 never-smokers.
The smokers were 2.4 times as likely as non-smokers to have primary progressive MS. 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.
The MRI scans showed that over time, smokers had 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.
The authors note some components of cigarette smoke are known to have toxic effects on brain and neural tissue. For example, cyanides have been found to destroy nerve cells' myelin coating (a characteristic feature of MS) in animals.
Smoking might also have effects on the immune system. As well, smoking increases the frequency and duration of respiratory infections, "which have been linked to risk of MS and to the occurrence of MS relapses," the authors write.
The authors say their 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."
