Cognitive dysfunction in patients with mildly disabling relapsing-remitting multiple sclerosis: an exploratory study with diffusion tensor MR imaging.

Previous studies assessing the magnetic resonance imaging (MRI) correlates of cognitive dysfunction in multiple sclerosis (MS) achieved conflicting results. Diffusion tensor (DT)-MRI provides metrics that are sensitive to the macro- and microscopic MS lesion load with increased specificity to the more destructive aspects of MS pathology than conventional imaging. We performed an exploratory study to assess the magnitude of the correlation between quantities derived from DT-MRI and measures of cognitive impairment in patients with relapsing-remitting (RR) MS.T2, T1, DT-MRI scans of the brain and an extensive battery of neuropsychological tests (exploring language, complex reasoning, attention and memory) were obtained from 34 RRMS patients. We measured T2 and T1 lesion volumes (LV) and brain volume. Average lesion mean diffusivity (D) and fractional anisotropy (FA) were calculated. D and FA histograms from the brain tissue (BT), the normal-appearing brain tissue (NABT), the normal-appearing white matter (NAWM) and the normal-appearing gray matter (NAGM) were also obtained. Nine patients (26.5%) were found to be cognitively impaired. Moderate correlations were found between symbol digit modalities test, verbal fluency test and 10/36 spatial recall test scores and T2 LV, T1 LV and average lesion, WBT, NABT, NAWM and NAGM values (r values ranging from -0.30 to -0.53). No correlations were found between any of the neuropsychological test scores and brain volume, average lesion FA and WBT FA.DT-MRI provides quantitative metrics that seem to reflect the severity of language, attention and memory deficits in patients with RRMS. This study also suggests that the extent and the intrinsic nature of the macroscopic lesions as well as the damage of the NAWM and NAGM all contribute to the neuropsychological deficits of RRMS patients.