Socioeconomic status and disability progression in multiple sclerosis

OBJECTIVE: To examine the association between socioeconomic status (SES) and disability outcomes and progression in multiple sclerosis (MS). METHODS: Health administrative and MS clinical data were linked for 2 cohorts of patients with MS in British Columbia (Canada) and South East Wales (UK). SES was measured at MS symptom onset (±3 years) based on neighborhood-level average income. The association between SES at MS onset and sustained and confirmed Expanded Disability Status Scale (EDSS) 6.0 and 4.0 and onset of secondary progression of MS (SPMS) were assessed using Cox proportional hazards models. EDSS scores were also examined via linear regression, using generalized estimating equations (GEE) with an exchangeable working correlation. Models were adjusted for onset age, sex, initial disease course, and disease-modifying drug exposure. Random effect models (meta-analysis) were used to combine results from the 2 cohorts. RESULTS: A total of 3,113 patients with MS were included (2,069 from Canada; 1,044 from Wales). A higher SES was associated with a lower hazard of reaching EDSS 6.0 (adjusted hazard ratio aHR 0.90, 95% confidence interval CI 0.89-0.91), EDSS 4.0 (aHR 0.93, 0.88-0.98), and SPMS (aHR 0.94, 0.88-0.99). The direction of findings was similar when all EDSS scores were included (GEE: β = -0.13, -0.18 to -0.08). CONCLUSIONS: Lower neighborhood-level SES was associated with a higher risk of disability progression. Reasons for this association are likely to be complex but could include factors amenable to modification, such as lifestyle or comorbidity. Our findings are relevant for planning and development of MS services.