Cognitive function predicts work disability among multiple sclerosis patients

Background: In multiple sclerosis various aspects of cognitive function can be detrimentally affected. More than that, patients' employment and social functioning is likely to be impacted. Objective: To determine whether work disability among multiple sclerosis patients could be predicted by the symbol digit modalities test. Methods: A register-based cohort study was conducted. Individual data on work disability, operationalised as annual net days of sickness absence and/or disability pension were retrieved at baseline, when the symbol digit modalities test was performed, after one-year and 3-year follow-up for 903 multiple sclerosis patients. The incidence rate ratios for work disability were calculated with general estimating equations using a negative binomial distribution and were adjusted for gender, age, educational level, family composition, type of living area and physical disability. Results: After one year of follow-up, the patients in the lowest symbol digit modalities test quartile were estimated to have a 73% higher rate of work disability when compared to the patients in the highest symbol digit modalities test quartile (incidence rate ratio 1.73, 95% confidence interval 1.42-2.10). This estimate after 3-year follow-up was similar (incidence rate ratio 1.68, 95% confidence interval 1.40-2.02). Conclusion: Cognitive function is to a high extent associated with multiple sclerosis patients' future work disability, even after adjusting for other factors.