Regional and cellular pathology in frontotemporal dementia: relationship to stage of disease in cases with and without Pick bodies

Frontotemporal dementia (FTD) is a prevalent neurodegenerative disease of heterogeneous histopathology. Neuropathological subtypes are identified on the basis of the presence or absence of tau- or ubiquitin-positive neuronal inclusions. Our recent work has established four disease stages that are independent of neuropathological subtype and reflect the clinical and degenerative progression observed in FTD. The variability in the extent of neuronal loss, astrogliosis, and microvacuolation are, therefore, more likely to reflect disease stage with potentially predictable differences between cases at early versus late disease stages. Understanding the variability in these parameters may assist in determining the importance of diverse disease subtypes in FTD. We examined 21 cases of sporadic, behavioural variant FTD and quantified the progression of histopathological change. The neuropathology of early disease was marked by severe astrogliosis of both the frontal and temporal cortices and neuronal loss, which was more evident in upper cortical layers of the frontal lobe. In late disease, neuronal loss was evident from both layer III and V in frontal and temporal cortices, and particularly the CA1 sector of the hippocampus. In addition, we compared the neuropathology of Pick's disease, dementia lacking distinctive histopathology and FTD with motor neuron disease, and found no difference in these pathological subtypes on the basis of neuronal loss, astrogliosis or microvacuolation. These results show that the earliest cellular changes in FTD occur in glia, and that disease stage rather than FTD subtype determines the pattern and extent of neuronal degeneration.