Cigarette smoking is certainly no good for you, but it may not necessarily make your primary progressive multiple sclerosis (PPMS) worse, a new study finds.
The study, “Smoking does not influence disability accumulation in primary progressive multiple sclerosis,” appeared in the European Journal of Neurology. It contradicts what was previously reported for relapsing-remitting MS (RRMS) patients — suggesting that the underlying mechanisms driving these two manifestations of MS are different.
Doctors have long known that smoking is a risk factor for MS, with most studies focusing on RRMS.
“Cigarette smokers have a higher risk of developing MS, an increased risk of conversion to clinically definite MS, an increased risk of reaching Expanded Disability Status Scale (EDSS) scores 4 and 6, and an increased number of demyelinating magnetic resonance imaging (MRI) lesions,” the researchers wrote. Yet its long-term effect on worsening disability in PPMS patients is still elusive.
Researchers at Canada’s University of Calgary in Alberta have now investigated this possible link by retroactively analyzing data collected from the ongoing Clinical Impact of Multiple Sclerosis study. From an initial pool of 4,862 patients with clinically definite MS, they identified 500 with PPMS, of which 416 (or 83 percent) had available smoking history. Outcomes included the time from disease onset to EDSS 4 and 6, and the time from EDSS 4 to 6.
The analysis showed no significant association between cigarette smoking and disability accumulation in PPMS. The median time to EDSS 4 was four years for patients who had always smoked, and five years for never-smokers; for an EDSS of 6, the median time was nine years for both long-term and never-smokers.
Additionally, PPMS patients who smoked showed no increased risk of reaching EDSS scores 4 and 6, nor of quickly progressing from EDSS 4 to 6.
Rather, age at disease onset was found to be the strongest risk factor for progression to EDSS 4 and 6, and from EDSS 4 to 6.
“This finding is in contrast to the influence of smoking on relapses, MRI lesions and disability accumulation in relapsing remitting disease which suggests that cigarette smoking may only contribute to inflammatory outcomes in relapse-onset MS,” researchers wrote.
Overall, the team concluded that there is “no association between cigarette smoking and disability accumulation and that age at disease onset remains the strongest prognostic factor for long-term outcomes in primary progressive MS. Our findings support the idea that disability accumulation in relapsing remitting MS and primary progressive MS depend on different underlying pathomechanisms, which are further differentially influenced by cigarette smoking.”