MRI Abnormalities in MS Vary With Distance From Lesions
More axonal swellings in normal-appearing white matter close to MS white matter lesions
FRIDAY, Dec. 16 (HealthDay News) -- Magnetic resonance imaging (MRI) abnormalities in normal-appearing white matter (NAWM) in multiple sclerosis (MS) brains vary with the distance from the white matter (WM) lesion, according to a study published online Dec. 7 in the Annals of Neurology.
Natalia M. Moll, M.D., Ph.D., from the Lerner Research Institute in Cleveland, and colleagues examined the pathologic basis of subtle abnormalities in magnetization transfer ratio (MTR) and diffusion tensor imaging (DTI) parameters observed in NAWM in MS brains. A rapid post-mortem protocol which included in situ MRI was used to obtain brain tissues. A total of 48 regions of interest (ROIs) obtained from four secondary progressive MS brains were analyzed for four types of MRI-defined ROIs: regions abnormal on all images (T2T1MTR lesions); NAWM regions with slightly abnormal MTR located close to WM lesions (sa-WM Close) or far from WM lesions (sa-WM Far); and NAWM regions with normal MTR (NAWM), all of which were analyzed immunohistochemically.
The investigators identified significantly more axonal swelling in sa-WM Close ROIs. Compared with NAWM, more enlarged major histocompatibility complex II+ microglia and macrophages were seen in sa-WM Far, sa-WM Close, and T2T1MTR lesions. MTR and DTI measures across all ROIs were moderately associated with myelin density, axonal area, and axonal counts. When T2T1MTR lesions were excluded from the analysis, nonlesional WM MTR and DTI measures were found to be associated with activated microglia, but not with axonal or myelin integrity.
"The pathologic substrates for MRI abnormalities in NAWM vary based on distance from focal WM lesions," the authors write.