Background: Using diffusion tensor imaging (DTI), it was previously found that demyelinated gray matter (GM) lesions have increased fractional anisotropy (FA) when compared to normal-appearing gray matter (NAGM) in multiple sclerosis (MS). The biological substrate underlying this FA change is so far unclear; both neurodegenerative changes and microglial activation have been proposed as causal contributors.
Objective: To test the proposed hypothesis that microglia activation is responsible for increased FA in cortical GM lesions.
Methods: We investigated post-mortem cortical DTI changes in hemispheric, coronally cut sections and investigated the underlying histopathology using immunohistochemistry.
Results: Overall, there were few activated microglia/macrophages, and no difference between GM lesions and NAGM was observed. However, cell density was increased in GM lesions compared to NAGM (309.67 ± standard deviation (SD) 124.44 vs 249.95 ± SD 56.75, p = 0.002).
Conclusion: FA increase was not due to lesional and non-lesional differences in microglia activation and/or proliferation. We found an increase in general cellular density without a notable difference in cellular size, that is, tissue compaction, as a possible alternative explanation.
Keywords: 7T MRI; DTI; FA; MD; cortical lesions; histopathology; multiple sclerosis.
© The Author(s), 2016.