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Smoking was linked with worse motor disability in people with multiple sclerosis (MS), but quitting smoking appeared to ameliorate that.

In a large observational study of people with confirmed MS, current smoking was tied to shorter times to worsening in motor skills, walking ability, anxiety, and depression, said Jeff Rodgers, PhD, of Swansea University in Wales, in a presentation at the European Committee for Treatment and Research in Multiple Sclerosis (ECTRIMS) Congress.

"Smoking causes real disability progression and mood worsening in people with MS," Rodgers said. "But when you stop smoking, that worsening stops as well."

The research, published in , showed that quitting smoking led to a slower motor disability deterioration rate so that it matched the rate of motor decline in people who had never smoked.

While the negative effect of smoking in MS has been well established, there's less evidence about whether stopping smoking is beneficial to MS progression, the researchers said.

Rodgers and colleagues evaluated data from 2011 to 2020 for 7,983 people with confirmed MS in the , an online registry in which participants enter data regularly. For this study, the researchers focused on three patient-reported outcomes: the MS Physical Impact Scale (MSIS-29-Phys), a measure of motor skills; the MS Walking Scale (MSWS-12), a measure of walking ability; and the Hospital Anxiety and Depression Scale (HADS-Anxiety and HADS-Depression). Smoking status was confirmed against clinical records.

For time-to-event analysis, primary outcomes were a clinically significant 10-point increase in the MSIS-29-Phys or MSWS-12 score, or a 2-point increase in the HADS-anxiety and HADS-Depression score.

A total of 4,130 people in the study had smoked, including 1,315 current smokers and 2,815 former smokers. At baseline, former smokers were older (mean age about 51) than current smokers (mean age about 45), and were more likely to have a progressive diagnosis. Never smokers were more likely to be women and more likely to be using disease-modifying treatment.

At the time of completing their first questionnaire, current smokers had higher scores indicating higher disability compared with people who had never smoked: approximately 10 points difference in MSIS-29-Phys and MSWS-12, and 1.5-1.8 point difference in HADS-anxiety and HADS-depression.

Among 923 participants followed prospectively, MSIS-29-Phy, MSWS-12, and HADS-Depression scores worsened over 4 years, while HADS-Anxiety remained stable. At year 4, current smokers had higher a MSIS-29-Phys score (3.05) while former smokers had lower a MSIS-29-Phys score (-2.91). Current smokers also had higher HADS-Anxiety scores at year 4.

Of 4,642 participants in the time-to-event analysis, current smoking was associated with a shorter time to worsening in all outcomes: MSIS-29-Phys (P=0.0013), MSWS-12 (P=0.0061), HADS-Anxiety (P=0.0017), and HADS-Depression (P<0.0001).

Worsening in motor disability -- MSIS-29-Phys and MSWS-12 scores -- was independent of baseline HADS-Anxiety and HADS-Depression scores. There was no statistically significant difference in the rate of worsening between never smokers and former smokers.

One limitation of the analysis was that the U.K. MS Register uses self-reported data. As an observational study, causality could not be established. Selection bias may have occurred and reverse confounding may have been a factor in some patient-reported outcomes.