An autopsied case of corticobasal degeneration presenting with frontotemporal dementia followed by myoclonus

A Japanese woman developed frontotemporal dementia (FTD)‐like symptoms of abnormal behavior, such as stereotyped behavior and disinhibition. The patient developed these symptoms at the age of 59 years, although aphasia symptoms were not apparent at early disease stages. Progressive parkinsonism was dominant on the left side, and conspicuous myoclonus was recognized in the late disease stage. MRI indicated severe, right side‐dominant frontotemporal lobe atrophy with white matter degeneration. Brainstem and cerebellar atrophy were also observed. The patient underwent gastrostomy 7 years after the onset of her symptoms and died at the age of 70 years. Neuropathological examination showed diffuse neuron loss with gliosis and tissue rarefaction in the frontotemporal lobe, particularly in the right anterior portion of the frontal lobe. Spongiform changes and ballooned neurons were also observed in the frontotemporal cortex, particularly in the superficial layer and deeper layers, respectively. Gallyas‐Braak silver staining and anti‐phosphorylated tau immunostaining indicated numerous argyrophilic and tau‐positive structures, including pretangles, astrocytic plaques, coiled bodies and neuropil threads. We speculate that the myoclonus observed in the present case was at least partly caused by or related to the spongiform change and ballooned neurons in the cerebral cortex. The clinical phenotypes of corticobasal degeneration (CBD) vary considerably, and the clinical presentation of the present patient was compatible with frontal behavioral‐spatial syndrome in the early disease stage. However, in the later disease stages, her symptoms were reflective of corticobasal syndrome. Because it is not rare for the clinical phenotype to change along with disease progression in cases of CBD, we should consider CBD in cases presenting with FTD at symptom onset.