Presence of cortical lesions in older persons with multiple sclerosis and association with cognitive function

Background Cortical lesions (CL) have been reported and characterized in multiple sclerosis (MS), but their presence and association with cognitive function in older adults with MS (OAMS) have not been evaluated. Objective To quantify the presence of CL in OAMS and healthy controls. We hypothesized that compared to controls, OAMS would have more CL, and CL would be associated with worse cognition. Methods OAMS (n = 95, mean age 64.5 +/- 4.2) and controls (n = 106, mean age 68.3 +/- 7.3) underwent MRI and cognitive assessments. Cognitive function was assessed through Symbol-Digit-Modalities-Test (SDMT). Results CL were identified in 43/95 (45%) of OAMS, and 2/106 (1.9%) of controls. OAMS were further stratified by CL burden (0, 1-2, and >= 3 CL). Linear regressions showed that compared to participants with no CL, those with >= 3 CL, but not 1-2 CL demonstrated worse SDMT performance in unadjusted (p = 0.005) and adjusted (p = 0.034) analyses. Stratification of results by age of onset into typical (TOMS) and late (LOMS) onset MS, show that among LOMS white matter lesion load (WMLL), but not CL burden, is associated with worse SDMT (p < 0.001). In contrast, CL burden in TOMS was associated with lower SDMT performance (p = 0.021), independent of WMLL. Conclusion CL are present in OAMS and are significantly greater than in controls. Among OAMS, higher CL burden was associated with worse speed of processing and working memory performance. Age of MS onset modified the effect CL burden has on SDMT performance, which suggests that there may be different disease processes between LOMS and TOMS that affect cognitive performance.