A clinical and neuropathological study of an unusual case of sporadic tauopathy. A variant of corticobasal degeneration?

We report a sporadic case of tauopathy with unusual clinical and neuropathological features. The patient presented with progressive symmetric rigid-akinetic parkinsonism and dementia of the subcortical type. Magnetic resonance imaging of the brain revealed atrophy resembling multiple system atrophy. The level of cerebrospinal fluid tau protein phosphorylated at serine 199 was markedly elevated. The autopsy revealed more glial than neuronal tauopathy, with much heavier involvement of subcortical white matter and the brainstem than of the cerebral cortex. Analysis of dephosphorylated tau revealed that hyperphosphorylated four-repeat tau isoforms were deposited in the brain of the patient. Despite morphological and biochemical resemblance to a certain form of familial fronto-temporal dementia, no mutation of the tau gene including exon 10 could be found. Our findings, taken together with those in previous similar case reports, indicate that the case represents an atypical form of corticobasal degeneration or a new variant of sporadic tauopathy.