Neuronal and glial tau pathology in early frontotemporal lobar degeneration-tau, Pick's disease subtype

Frontotemporal lobar degeneration-tau, Pick's disease subtype (PiD) is one of the major types of frontotemporal dementia, but its pathogenesis and disease mechanisms remain unclear. Here, we report a case of very early PiD. The patient was a 63-year-old healthy woman without dementia or any apparent psychosis. She was admitted to the hospital with multiple organ failure, and died three days later. The brain weighed 1050g and showed focal atrophy of the parahippocampal gyrus and right medial temporal lobe. Microscopically, neuronal loss and gliosis were limited to the atrophic areas. Surprisingly, Pick bodies (PiBs) and ballooned neurons were abundant throughout the bilateral temporal cortices, including the dentate gyrus. Cortical lamination of PiBs was predominant in the upper layer (layer II>VI), and the size of early PiBs tended to be smaller than that in severely affected areas. Numerous glial tau-positive inclusions (astrocytic inclusions, oligodendroglial coiled bodies, and threads) were found not only in the cerebral cortex but also in the temporal white matter. The neuropathological findings in this case suggest that PiB formation started long before the appearance of clinical symptoms and that PiB formation originating from small neurons may differ from other tau aggregations such as neurofibrillary tangles.