Whole-brain diffusion MR histograms differ between MS subtypes

Objective: To determine whether quantitative whole-brain MR diffusion histograms in patients with MS differ from those of normal control subjects. Background: MRI detects macroscopic cerebral lesions in MS, but the white matter lesion burden on MRI correlates imperfectly to clinical disability. Previous reports have further suggested abnormalities in white matter of MS patients with no visible lesions on conventional MRI. Methods: A total of 25 subjects (13 with MS [9 relapsing-remitting, 4 secondary progressive] and 12 healthy control subjects) underwent diffusion-weighted echoplanar MRI encompassing the entire brain. The average apparent diffusion coefficient (ADC(ave), or diffusion trace) was calculated on a pixel-by-pixel basis after segmentation of intracranial space from calvarium and extracranial soft tissues. Whole-brain ADC, histograms were calculated and plotted for statistical comparison. Results: Mean whole-brain MR ADC(ave) in MS patients was elevated and histograms were shifted to higher values compared with normal control subjects. Mean whole-brain ADC(ave) of secondary progressive patients was shifted to higher values compared with relapsing-remitting patients. Whole-brain ADC(ave) histograms of relapsing-remitting patients showed no significant difference from normal control subjects. Conclusion: Whole-brain MR diffusion histograms may quantitate overall cerebral lesion load in patients with MS and may be able to discern differences between clinical subgroups.