Cognitive impairment in a population-based study of patients with multiple sclerosis: differences between late relapsing-remitting, secondary progressive and primary progressive multiple sclerosis.

Background And Purpose: Few studies have investigated the differences in cognitive skills between the three subtypes of multiple sclerosis (MS) and they confounded the course of the disease with the duration of the disease and the physical disability. Moreover, they were not population based.

Methods: This was a retrospective analysis of cognitive testing from the database of a French programme for MS care. The pattern and the frequency of cognitive impairment in secondary progressive (SP), primary progressive (PP) and late relapsing-remitting (LRR, disease duration of more than 10 years) MS were compared.

Results: A total of 101 patients with MS (41 LRRMS, 37 SPMS, 23 PPMS) were included. 63.0% had a significant cognitive impairment. After controlling for age, sex, Expanded Disability Status Scale, disease duration and education level, patients with SPMS were at least 2-fold more frequently impaired than patients with LLRMS in information processing speed (P = 0.005), executive functions (P = 0.04), verbal fluency (P = 0.02), verbal episodic memory (P = 0.04), working memory (P = 0.02) and visuospatial construction (P = 0.01). The number of patients with at least one or two deficient cognitive domain(s) was higher in the SPMS group than in the LRRMS group (P = 0.002 and P < 0.001). Patients with PPMS were more frequently impaired in verbal fluency (P = 0.046) than patients with LRRMS and they more often presented at least one impaired cognitive domain (P = 0.03). SPMS and PPMS groups differed only for visuospatial construction (P = 0.02).

Conclusion: In this population-based study, patients with a progressive subtype of MS were more frequently and more severely impaired than patients with RRMS, even after more than 10 years of disease.