Clinical significance of atrophy and white matter mean diffusivity within the thalamus of multiple sclerosis patients

Background: Gray-matter (GM) atrophy is strongly predictive of cognitive impairment in multiple sclerosis (MS) patients. The thalamus is the region where the atrophy/cognition correlation is most robust. However, few studies have assessed diffusion tensor imaging (DTI) metrics within the thalamus. Objective: This study was designed to determine if thalamus white matter DTI predicts cognitive impairment after accounting for the effects of volume loss. Methods: We enrolled 75 MS patients and 18 healthy controls undergoing 3T brain magnetic resonance imaging (MRI). Thalamus volumes were calculated on 3D T1 images. Voxelwise analyses of DTI metrics were performed within the thalamic white matter tracts. Neuropsychological (NP) testing, acquired using consensus standard methods, contributed measures of memory, cognitive processing speed and executive function. Results: All cognitive tests were significantly predicted (R-2 =0.31, p<0.001) by thalamus volume after accounting for influence of demographics. Mean diffusivity was retained in regression models predicting all cognitive tests, adding from 7-13% of additional explained variance (p<0.02) after accounting for thalamus volume. Conclusions: We confirm the significant role of thalamus atrophy in MS-associated cognitive disorder, and further report that subtle thalamus pathology as detected by DTI adds incremental explained variance in predicting cognitive impairment.