Cognitive impairment after three decades of multiple sclerosis

Background: Population-based studies of cognitive impairment in patients with multiple sclerosis (MS) with long disease duration are limited. The aim of this study was to evaluate long-term outcome and the predictors of cognitive impairment in a cohort of patients with MS. Methods: Patients living in Oslo, Norway, with definite MS and onset in 1940-1980 alive on 1 May 2006 were included. Disability was assessed by Expanded Disability Status Scale (EDSS). Cognitive functioning was assessed in terms of psychomotor speed, attention, learning/memory and executive functions. Results: A total of 123 patients was included. EDSS was < 3.0 in 26% and >= 6.0 in 60% after mean disease duration of 34.5 years. Cognitive impairment was found in 48% of the patients eligible for neuropsychological evaluation (n = 84). Typical pattern was moderate impairment within areas of information processing, attention and memory. In the univariate analysis, younger onset age was significantly associated with cognitive impairment (P = 0.014). Younger onset age (P = 0.017) and disease course (secondary progressive vs. relapsing-remitting MS, P = 0.049) were significantly associated with cognitive impairment in the multivariate analysis. Conclusions: After three decades of disease, half of the MS patients experienced reduced cognitive functioning; however, nearly one-third of the patients were only mildly disabled based on the EDSS. Younger onset age was associated with higher prevalence of cognitive impairment. A thorough evaluation of cognitive function in addition to EDSS is essential for evaluating long-term impairment in patients with MS.