Hippocampal sclerosis with four-repeat tau-positive round inclusions in the dentate gyrus: a new type of four-repeat tauopathy.

Hippocampal sclerosis is defined as selective neuronal loss and gliosis of the hippocampus with heterogeneous etiologies, including neurodegenerative tauopathies. We report a 78-year-old woman who presented with depression, in whom postmortem examination revealed almost complete loss of neurons with gliosis in the subiculum and CA1-3 regions of the hippocampus and abundant neuronal cytoplasmic inclusions in the dentate gyrus. The inclusions were round, slightly basophilic and argyrophilic, resembling Pick bodies. However, they were Gallyas- and 4-repeat tau-positive, and 3-repeat tau- and ubiquitin-negative. To our knowledge, the histopathological features in this case were different from those in hippocampal sclerosis or 4-repeat tauopathies reported previously. It is likely that this case is a new variant of 4-repeat tauopathy presenting with hippocampal sclerosis.