Research: lesion location and cognitive impairment

Epub: Rossi et al . Relevance of Brain Lesion Location to Cognition in Relapsing Multiple Sclerosis. PLoS One. 2012;7(11):e44826.

OBJECTIVE: To assess the relationship between cognition and brain white matter (WM) lesion distribution and frequency in patients with relapsing-remitting multiple sclerosis (RR MS).
METHODS: MRI-based T2 lesion probability map (LPM) was used to assess the relevance of brain lesion location for cognitive impairment in a group of 142 consecutive patients with RRMS. Significance of voxelwise analyses was p<0.05, cluster-corrected for multiple comparisons. The Rao Brief Repeatable Battery was administered at the time of brain MRI to categorize the MS population into cognitively preserved (CP) and cognitively impaired (CI). 

RESULTS: Out of 142 RRMS, 106 were classified as CP and 36 as CI. Although the CI group had greater WM lesion volume than the CP group (pā€Š=ā€Š0.001), T2 lesions tended to be less widespread across the WM. The peak of lesion frequency was almost twice higher in CI (61% in the forceps major) than in CP patients (37% in the posterior corona radiata). The voxelwise analysis confirmed that lesion frequency was higher in CI than in CP patients with significant bilateral clusters in the forceps major and in the splenium of the corpus callosum (p<0.05, corrected). Low scores of the Symbol Digit Modalities Test (Cognitive disability test) correlated with higher lesion frequency in these WM regions.

CONCLUSIONS: Overall these results suggest that in MS patients, areas relevant for cognition lie mostly in the commissural fibre tracts. This supports the notion of a functional (multiple) disconnection between grey matter structures, secondary to damage located in specific WM areas, as one of the most important mechanisms leading to cognitive impairment in MS.

In this study they looked at cognitive impairment in RRMSers and found about 25% with some form of cognitive impairment. Those MSErs tended to have a higher lesion load in the white matter. Lesions in the commissural fibre tracts such as the corpus callosum, which is the nervous highway between the different sides of the brains correlates with cognitive function. Therefore it may not only be the direct grey matter damage that is central to the problem of cognition but how the white matter damage then impinges on grey matter function that is very important in whether cognitive impairment develops.

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