Hippocampal sclerosis dementia: a reappraisal

Hippocampal sclerosis (HpScl) is characterized by neuronal loss and gliosis in CA1 and subiculum of the hippocampus, and may be one contributing factor to dementia in old age. The term hippocampal sclerosis dementia (HpSclD) designates the presence of both hippocampal sclerotic lesions and a dementia syndrome. In the present review, we outline the pathological heterogeneity underlying HpSclD and discuss related disorders due to tau protein pathology and frontotemporal dementia with ubiquitin positive inclusions (FTLD-U). We also provide a detailed morphological description of ten of our own autopsied HpSclD cases, and compare these pathological findings with those reported in the literature. The lateralization of HpScl and the atrophy of the mammillary bodies were striking features in most of our cases. The main pathology consisted of tau positive lesions with a predominance of neuronal and glial pretangles in Ammon's horn and the dentate gyrus. Neurofibrillary and ghost tangles in CA1 and the subiculum were scarce and thus insufficient to explain the hippocampal pyramidal cell loss. In some cases, tau pathology in the hippocampal formation coexisted with glial tau pathology in the frontal cortex. The most striking finding besides the tau pathology was the presence of concomitant neuronal cytoplasmic inclusions and neurites immunoreactive for the transactive response DNA-binding protein-43 (TDP-43) in the dentate gyrus and temporal neocortex, similar to those found in FTLD-U. Taken together, the pathology of HpSclD is indicative of a degenerative rather than a hypoxic/ischemic etiology of HpSclD. Presently, HpSclD may best be deemed a disorder with various neurodegenerative etiologies, most notably tauopathy and TDP-43 proteinopathy (i.e. FTLD-U). Each of these disease processes could either independently or concertedly account for the dementia syndrome in HpSclD.