Current, Passive Smoking, and Snuff Use Impact Disease Progression in MS

Both current smoking and passive smoking, also known as secondhand smoke, negatively impact disease progression in multiple sclerosis (MS), according to findings from 2 population-based, case-control studies published in the Journal of Neurology, Neurosurgery, and Psychiatry.

Smoking is a known modifiable risk factor in individuals with MS, with smoking cessation as an important lifestyle modification. Patients with MS who are smokers have been shown to have higher Expanded Disability Status Scale (EDSS) scores compared with nonsmokers, along with greater brain atrophy and increased disease activity on magnetic resonance imaging. Some patients, however, have expressed “insecurity about whether nicotine replacement therapy would be safe in MS or in combination with MS disease-modifying treatment.”

For the study, researchers assessed the impact of smoking habits, exposure to passive smoking, and use of snuff (a smokeless tobacco product) on disease progression, quality of life, and cognitive performance in individuals with MS. They followed patients with MS from 2 case-control studies conducted via the Swedish MS Registry — Epidemiologic Investigation of Multiple Sclerosis (EIMS) and Genes and Environment in Multiple Sclerosis (GEMS) — with the use of both clinical and self-reported outcomes measures.

A total of 3,567 incident cases were recruited to EIMS from hospital-based neurology units between April 2005 and December 2019. In contrast, GEMS identified a total of 6,148 prevalent cases from the Swedish MS Registry between November 2009 and November 2011. Overall, 94% (9089 of 9715) of these patients were followed up with EDSS scores in the Swedish MS Registry. All participants were categorized according to their tobacco exposure at diagnosis regarding changes in EDSS, Multiple Sclerosis Impact Scale 29 physical score (MSIS-29-PHYS), and Symbol Digit Modalities Test (SDMT): never smokers (4.04%), current smokers (31.9%), and past smokers (27.7%).

In an effort to evaluate changes in severity/disability over time, baseline was defined as “the date of the first recorded EDSS at the time of diagnosis or later.” Confirmed disability worsening (CDW) was defined as “an increase in the EDSS Score with at least 1-point from baseline sustained between two follow-up visits separated in time by no less than 6 months. . .” The mean participant age at baseline was 37.6 and 72% were women.

Secondary outcomes included a change in health-related quality of life, based on the MSIS-29-PHYS. An increased score of ≥7.5 points in the physical and mental components of the MSIS-29-PHYS was defined as “a worsening from the patient’s perspective.”

Researchers found that at baseline, current smokers exhibited significantly higher EDSS scores than nonsmokers (0.48; 95% CI, 0.38-0.58). A more rapid increase in EDSS was reported both in current smokers (βcurrent smoking×time= 0.03, 95% CI, 0.02-0.04) and prior smokers (βpast smoking×time= 0.02, 95% CI, 0.01-0.03) compared with never smokers.

Higher MSIS-PHYS-29 scores were reported among both current smokers (6.61; 95% CI, 5.43-7.80) and prior smokers (1.21; 95% CI, –0.02 to 2.44), although the rates of change in MSIS-PHYS-29 scores remained stable over time. Lower SDMT scores at baseline were observed in current smokers (–3.64; 95% CI, –4.50 to –2.78). During follow-up, prior smoking compared with never smoking was linked to a more rapid decline in SDMT scores (βpast smoking×time = -0.27, 95% CI, –0.43 to –0.10).

Additionally, at baseline, current smoking vs never smoking was associated with an elevated risk for the development of CDW (adjusted hazard ratio [aHR], 1.13; 95% CI, 1.06-1.21), as well as an increased risk for achieving EDSS 3 (aHR, 1.21; 95% CI, 1.09-1.34) and EDSS 4 (aHR, 1.31; 95% CI, 1.14-1.51). In contrast, prior smoking at baseline was not significantly associated with any of these outcome variables.

A borderline significant inverse association was reported between the use of snuff and EDSS at baseline, compared with individuals who had never used snuff. Prior snuff users vs never snuff users had a significantly lower risk for CDW (HR, 0.84; 95% CI, 0.73-0.97), as well as a lower risk for attaining EDSS 3 (HR, 0.80; 95% CI, 0.63-1.00) and EDSS 4 (HR, 0.81; 95% CI, 0.63-1.14). Further, current use of snuff was significantly associated with a lower risk for achieving EDSS 4, but not with a risk for achieving EDSS 3 or CDW. The mean duration of snuff use was 9.4 years compared with 17.8 years among current users vs prior snuff users.

Several limitations of the study warrant mention. Information related to smoking and snuff use in EIMS obtained at baseline should be subjected to recall bias; however, data on lifestyle habits were collected retrospectively in GEMS. Further, it is possible that self-reported tobacco consumption habits may have been underreported.

“Our findings indicate that both smoking and passive smoking have a negative influence on MS and that smoking cessation post diagnosis may be an important secondary preventive measure,” the researchers noted. They concluded, “Snuff use was associated with slower disease progression, suggesting that nicotine replacement therapy could be an attractive way to increase the chance of quitting smoking among patients with MS.”

Disclosure: Some of the study authors have declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.