These data confirm substantial neocortical volume loss in MS patients and suggest that neocortical GM pathology may occur early in the course of the disease in both RR and PP MS patients and contribute significantly to neurologic impairment. Although a proportion of this neocortical pathology may be secondary to WM inflammation, the extent of the changes suggests that, especially in patients with PP MS, an independent neurodegenerative process also is active.

Cortical atrophy was found only in cognitively impaired patients and was significantly correlated with a poorer performance on tests of verbal memory, attention/concentration, and verbal fluency. Gray matter pathology may contribute to the development of cognitive impairment in MS from the earliest stages of the disease.

Background : We previously reported selective decreases of neocortical volumes in patients with early relapsing-remitting (RR) multiple sclerosis (MS) with mild cognitive impairment, with a good correlation between cortical volumes and cognitive measures.Objective: To assess the relevance of gray matter changes over time to changes in cognition in RRMS.Design: A longitudinal survey after 2.5 years. Each patient underwent a magnetic resonance imaging (MRI) protocol identical to that performed at baseline; cognitive performance was reassessed with the Rao Brief Repeatable Battery of Neuropsychological Tests in Multiple Sclerosis. Setting: Two university MS clinics.Patients: Of 41 patients with RRMS who participated in the original cross-sectional study, 28 were available for the follow-up evaluation (18 women; mean±SD age, 37.1±8.9 years; mean±SD MS duration, 7.3±2.9 years; mean±SD Expanded Disability Status Scale score, 1.8±1.5). Main Outcome Measures:We measured the percentage of brain volume changes, normalized cortical volume (NCV) changes, and normalized deep gray matter volume changes on conventional T1-weighted MRIs and changes in lesion load on T2-weighted MRIs. The number of tests failed on the Rao Brief Repeatable Battery were used to classify the patients as cognitively deteriorating or stable or improving.Results: We identified 12 of 28 cognitively deteriorating and 16 of 28 stable or improving patients. These subgroups did not differ in the mean±SD percentage of brain volume changes (−2.1%±1.2% vs −1.3%±1.3%; P=.11), normalized deep gray matter volume changes (−2.1±2.8 mL vs −0.6±3.1 mL; P=.60), and changes in lesion load on T2-weighted MRIs (1.9±2.6 mL vs 1.6±2.3 mL; P=.73). However, NCV changes were significantly higher in deteriorating than in stable or improving patients (−43.0±18.9 mL vs −17.8 ± 26.6 mL; P = .007). In deteriorating patients, NCV changes were correlated with performance in a verbal fluency test (r=0.73; PϽ.001). In a regression model, only NCV changes were significantly associated with deteriorating cognitive performance (odds ratio, 0.8; 95% confidence interval, 0.7-0.9). Conclusion:Progressive neocortical gray matter loss is relevant to MS-associated cognitive impairment and may represent a sensitive marker of deteriorating cognitive performance in RRMS.

These findings emphasize the importance of including accurate neuropsychological testing and quantitative MR metrics in subjects with RIS suggestive of MS. They can provide a better characterization of these asymptomatic subjects, potentially useful for diagnostic and therapeutic decisions.

Cerebral NAA/Cr and MTr values are diffusely decreased in MS patients with early disease, low demyelinating lesion load, and no significant disability. This suggests that axonal and/or tissue injury begins very early in the course of MS and might be at least partially independent of cerebral demyelination.