Accumulation of cortical lesions in MS: relation with cognitive impairment

BACKGROUND: Gray matter (GM) lesions are frequently found in multiple sclerosis (MS) and their in-vivo detection has been improved using new magnetic resonance imaging sequences, such as double inversion recovery (DIR). However, little is known about progression of GM lesions over time. OBJECTIVE: To study the longitudinal behavior of GM lesions and to explore their relation to cognitive impairment in MS. METHODS: DIR images were acquired from 13 MS patients and seven healthy controls at two time points with a median interval of 3 years. At follow-up, all subjects underwent cognitive testing. Lesions were classified as white matter, cortical or hippocampal lesions. RESULTS: In patients, median cortical lesion number had increased from 18 to 26 at follow-up (P = 0.01), median white matter (WM) lesion number had increased from 56 to 65 (P = 0.02), and no significant increase over time was found for hippocampal lesions. Cortical lesion number at follow-up was significantly higher in secondary progressive (SP) than in relapsing-remitting patients. Significant relations were found between cortical and WM lesion number at follow-up on the one hand and visuospatial memory and processing speed on the other hand. Hippocampal lesion number was related to visuospatial memory. CONCLUSION: Cortical lesions increase significantly over a 3-year time period, are most frequent in SP patients, and are associated with cognitive impairment.