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An autopsied case of unclassifiable sporadic four‐repeat tauopathy presenting with parkinsonism and speech disturbances

A 48‐year‐old Japanese woman experienced slow‐onset parkinsonism and speech disturbances. Neurological examinations revealed rigidity in the trunk and extremities, bradykinesia and postural instability, although cognitive impairments and psychiatric symptoms were not apparent in the early disease stage. Neuroimaging revealed progressive bilateral frontotemporal lobe atrophy with cerebral blood flow hypoperfusion. No apparent signs of lower motor neuron involvement were observed, such as fasciculation or electromyogram findings. She eventually reached the akinetic mutism state, and gastrostomy and tracheotomy were performed at 4 years after onset. A clinical diagnosis of progressive supranuclear palsy was made prior to her death, which occurred 6 years after onset. Post mortem examinations revealed that the brain weighed 1200 g and showed atrophy of the frontotemporal lobe and brainstem. Severe neuron loss and gliosis were observed in the frontotemporal lobe. The superior and middle frontal gyri were the most severely affected and showed spongiform changes in the superficial layer. The globus pallidus, subthalamic nucleus, cerebellar dentate nucleus, substantia nigra and inferior olivary nucleus also showed neuronal loss with gliosis. Using hyperphosphorylated tau (AT‐8) immunostaining, pretangle‐like neurons, numerous short threads and glial tau pathology were extensively observed. Using Gallyas−Braak silver staining, thin and short threads were also extensively observed, but considerably fewer than those observed by AT‐8 immunostaining. Neither astrocytic plaques nor tuft‐shaped astrocytes were observed. Examination by immunoelectron microscopy showed straight fibrils approximately 15 nm in diameter in the neuronal cytoplasmic inclusions in the cerebral cortex and in the fibrillary structures in the cerebral white matter. Western blot analysis of sarkosyl‐insoluble tau revealed predominantly four‐repeat tau and a banding pattern similar to that seen in progressive supranuclear palsy. No pathogenic mutations were found during the gene analysis of microtubule‐associated protein tau. After completing our comprehensive investigation, we diagnosed this patient with unclassifiable four‐repeat tauopathy.