Cognitive impairment in relation to MRI metrics in patients with clinically isolated syndrome

Background: Cognitive deficits are frequent in multiple sclerosis (MS) and have been associated with morphologic brain changes. Less information exists on their extent and relation to MRI findings in clinically isolated syndrome (CIS). It is also unclear if structural changes as detected by magnetization transfer (MT) imaging may provide an additional explanation for cognitive dysfunction. Objective: To analyse the extent of cognitive deficits and their relation to MRI metrics including MT imaging in CIS compared to relapsing-remitting MS (RRMS). Methods: Forty-four CIS and 80 RRMS patients underwent the Brief Repeatable Battery of Neuropsychological Tests (BRB-N) and a 3 T MRI scan. Results: BRB-N subtests revealed similar results in CIS and RRMS. Impaired mental processing speed was most prevalent in both groups (CIS 13.6%; RRMS 16.3%) and thus served for correlation with MRI metrics. Using stepwise linear regression analyses, the strongest predictor for decreased mental processing speed was normalized cortex volume (p < 0.001) followed by T-2-lesion load (p < 0.05) in RRMS, whereas cortical MT ratio was the only MRI parameter associated with decreased mental processing speed in CIS (p < 0.005). Conclusion: Cognitive dysfunction occurs in CIS in a pattern similar to RRMS, with impaired mental processing speed being most prevalent. Cortical MT-ratio changes may be an early sign for tissue changes related to impaired mental processing speed in CIS while this association shifts to increased signs of cortical atrophy and lesion load in RRMS.