Corticodentatonigral degeneration; degenerative dementia syndrome characterized by the diffuse accumulation of pathologic tau proteins within neurons; clinical features reflect dysfunction predominantly of frontal and parietal cortices and include progressive memory loss, dysphasia, psychomotor slowing, apraxia, alien hand syndrome, asymmetric rigidity, dysphagia, postural instability, frontal release signs, oculomotor impairment, asymmetric hyper-reflexia, myoclonus, and hypokinetic dysarthria; pathology demonstrates asymmetrical frontoparietal atrophy with neuronal loss and gliosis, substantia nigra degeneration, and swollen achromatic neurons; MRI shows asymmetrical cortical atrophy most severe in the parietal lobes; positron emission tomography (PET) and single photon emission computed tomography reveal hypoperfusion and hypometabolism in affected areas; treatment involves symptomatic and supportive care; levodopa may occasionally result in modest reduction of rigidity.