Background: Smoking is associated with a more severe disease course in people with multiple sclerosis (MS). The magnitude of effect of smoking cessation on MS progression is unknown. The aim of this study was to quantify the impact of smoking cessation on reaching MS disability milestones.
Aims and methods: This is a cross-sectional study with retrospective reports. A comprehensive smoking questionnaire was sent to 1270 patients with MS registered between 1994 and 2013 in the Nottingham University Hospital MS Clinics database. Demographic and clinical data were extracted from the clinical database. Cox proportional hazard regression was used to estimate effects of smoke-free years on the time to Expanded Disability Status Scale (EDSS) scores 4.0 and 6.0. MS Impact Scale 29 and Patient Determined Disease Steps were used to assess the physical and psychological impact of smoking.
Results: Each "smoke-free year" was associated with 0.96 (95% confidence interval: 0.95 to 0.97) times decreased risk of reaching EDSS 4.0 and 0.97 (95% confidence interval: 0.95 to 0.98) times decreased risk of reaching EDSS 6.0. Nonsmokers showed a significantly lower level of disability in all the self-reported outcomes compared with current smokers.
Conclusions: The reduction in the risk of disability progression after smoking cessation is significant and time dependent. The earlier the patients quit, the stronger the reduction in the risk of reaching disability milestones. The quantitative estimates of the impact of smoking cessation on reaching disability milestones in MS can be used in interventional trials.
Implications: This study provides for the first time quantitative estimates of the effects of smoking cessation in MS, essential for informing smoking cessation trials. The clear effect of smoking cessation on MS progression suggests the need to consider adjusting for smoking cessation when assessing for treatment effects in clinical trials of treatments for MS. Smoking cessation should be an early intervention in people with MS.