This study assessed the correlation between cortical lesion load on 7T MRI and the magnetisation transfer ratio (MTR) of the normal appearing white matter (NAWM), in order to test the hypothesis that cortical lesions cause NAWM degeneration. It is known that NAWM axon loss, rather than focal demyelination in white matter lesions (WMLs), is the pathological substrate underlying chronic irreversible disability in MS.
Nineteen people with MS had a 7T MRI with MTR and magnetisation-prepared-rapid-acquisition-gradient-echo (MPRAGE) to identify cortical lesions. White matter lesions were segmented using MPRAGE images and then NAWM masks were produced by subtracting WML maps from white matter volume.
The researchers found that cortical lesion volumes and counts all had significant correlation with NAWM MTR, with the cortical lesion volumes showing the strongest correlation using MTR images. WML volume had no significant correlation with NAWM mean MTR. This supports the hypothesis that cortical lesions cause NAWM degeneration. Therefore, this correlation implicates cortical lesions in the pathogenesis of NAWM axon loss which underlies long term disability and progression in MS.
Authors: Mistry N, Abdel-Fahim R
Source: Mult Scler. 2013 Jul 15. [Epub ahead of print]
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