Chameleons and mimics: Progressive supranuclear palsy and corticobasal degeneration.

Progressive supranuclear palsy (PSP) and corticobasal degeneration (CBD) are neurodegenerative disorders that show parkinsonism as their main symptom. Both PSP and CBD are sporadic tauopathies associated with hyperphosphorylated four-repeat tau aggregation in neurons and glial cells. The characteristic pathologies of PSP are midbrain atrophy and the appearance of tufted astrocytes and globose-type neurofibrillary tangles. PSP shows severe degeneration in the globus pallidus, substantia nigra, subthalamic nucleus, and cerebellar dentate nuclei. Conversely, the characteristic pathologies of CBD are cortical atrophy and the appearance of astrocytic plaques and argyrophilic threads. CBD is associated with severe degeneration in the cerebral white matter, substantia nigra, and globus pallidus. Clinical symptoms depend on the topographical distribution and severity of degeneration rather than on the type of aggregated protein or inclusions. PSP and CBD present clinically differential diagnostic difficulties because of their overlapping pathological distributions.