Thalamic involvement in multiple sclerosis: A diffusion-weighted magnetic resonance imaging study

Background and Purpose. Injury to deep gray matter structures in multiple sclerosis (MS) has been suggested by recent neuroimaging and neuropathology studies. Diffusion-weighted magnetic resonance imaging (MRI) can assess tissue damage with greater sensitivity than conventional MRI. The authors' objective was to assess thalamic gray matter damage by diffusion-weighted imaging in MS patients. Methods. This was a retrospective study performed at a tertiary care, university-affiliated comprehensive MS center of 82 MS patients and 43 controls. The main outcome measures were thalamic apparent diffusion coefficients (ADCs), whole-brain atrophy (brain parenchymal fraction), fluid-attenuated inversion recovery (FLAIR) hyperintense lesion volume, and clinical course. Results. ADCs in the left thalamus were higher in MS patients (0.741 ± 0.044 × 10^-3 mm²/s) than controls (0.723 ± 0.036 × 10^-3 mm²/s) (P = .027) and higher in secondary progressive MS patients (0.761 ± 0.044 × 10^-3 mm ²/s) than relapsing-remitting MS patients (0.735 ± 0.032 × 10^-3 mm²/s) (P = .029). ADCs in the right thalamus were higher in secondary progressive MS patients (0.784 ± 0.069 × 10^-3 mm²/s) than controls (0.757 ± 0.038 × 10^-3 mm²/s) (P = .033). In the MS group, left thalamus ADCs correlated negatively with brain parenchymal fraction (r = -0.30, P = .008), total left hemispheric FLAIR lesion volume correlated with ADCs in the left (r = 0.35, P = .001) and right (r = 0.39, P < .001) thalami, and total right hemispheric FLAIR lesion volume correlated with ADCs in the left (r = 0.31, P = .006) and right thalami (r = 0.22, P = .048). Conclusion. MS patients have increased water diffusion in the thalamus that is partly associated with clinical course, lesion load, and whole-brain atrophy. Both indirect and direct mechanisms of gray matter injury may play a role in the pathophysiology of MS.