[Corticobasal degeneration]

Corticobasal degeneration (CBD) was first reported by Rebeiz et al as corticodentatonigral degeneration with neuronal achromasia in 1967. After Gibb et al described 7 cases including 4 cases from the literature under the term of corticobasal degeneration, CBD has become widely recognized. The disease starts mainly in one's fifties and sixties with the duration of 6 to 7 years. The clinical features include asymmetric parkinsonism, cerebral cortical signs, and others. Typically, patients present with unilateral clumsiness with akinetic-rigid syndrome and limb-kinetic apraxia. Postural instability, gait disturbance and involuntary movements such as dystonia are not uncommon. The parkinsonism is DOPA-resistant. BEsides apraxia, alien limb syndrome, cortical sensory disturbances, frontal lobe-release signs, and dementia are representative cortical signs. Other clinical features include dysarthria, pyramidal tract signs and supranuclear gaze palsy. MRI, SPECT or PET reveals asymmetric atrophy, decrease in blood flow or reduction in metabolism of the frontal parietal region around the central sulcus. Electrophysiological and magnetic stimulation studies demonstrated increase in excitability of the cerebral cortex. Myoclonus in CBD is cortical in origin but without any preceding potential or giant somatosensory evoked potential. Neuropathologically CBD is characterized by involvement of the particular cortices and substantia nigra. Other structures such as the putamen, pallidum, thalamus, subthalamus, cerebellar dentate nucleus and brainstem are affected to various extents. Histological features include achromatic, ballooned neurons as well as tau and Gallyas positive neuronal and glial intracytoplasmic inclusions. Astrocytic plaque is considered to be a form of glial inclusions specific to CBD. Diagnosis of typical cases of CBD appears easy but atypical cases were reported with showed dementia or aphasia as a main feature, or were devoid of the asymmetry of signs and symptoms. CBD, progressive supranuclear palsy and Pick's disease share both clinical and neuropathological features to some extent while they are clearly distinct among typical cases. The etiology and pathomechanism of CBD remain to be elucidated.