Associations of cognitive and behavioural impairment in ALS with brain pathology: pTDP-43 versus microglial activation

OBJECTIVE: Investigate associations between brain pathology (pTDP-43 inclusions and microglial activation) and cognitive and behavioural impairment in patients with amyotrophic lateral sclerosis (ALS).

METHODS: Based on comprehensive neuropsychological examination and behavioural assessment, 21 ALS patients of whom post mortem brain tissue was obtained, were classified as having 1) no cognitive and/or behavioural impairment (pure motor ALS), 2) mild cognitive and/or behavioural impairment (ALSci/bi), and 3) ALS with behavioural variant frontotemporal dementia (ALS-bvFTD). Immunohistochemical staining of pTDP-43 and HLA-DR-defined microglial activation was semi-quantitatively assessed in grey and/or white matter of the prefrontal cortex, thalamus, hippocampus, and motor cortex.

RESULTS: Fourteen patients had pure motor ALS, four patients had ALSci/bi, and three patients had ALS-bvFTD. pTDP-43 pathology in the grey matter of the prefrontal cortex and gyrus dentatus differed between groups, especially between pure motor ALS and ALS-bvFTD. For each extra-motor brain region, pTDP-43 severity was highest in patients with ALS-bvFTD and lowest in patients with pure motor ALS, with ALSci/bi in between. This pattern was not observed for microglial activation. Associations between white matter pTDP-43 severity and cognitive/behavioural impairment were less robust than those in grey matter.

CONCLUSION: Severity of cognitive and/or behavioural impairment in ALS is related to severity of pTDP-43 pathology, in particular in the grey matter of extra-motor brain regions; we did not detect a clear association with microglial activation.