Among the atypical parkinsonian syndromes, corticobasal degeneration (CBD) is probably the most challenging disorder to diagnose antemortem. It can present with multiple phenotypes, none of them specific enough to lead to an unequivocal diagnosis. Alternatively, multiple other neurodegenerative disorders with a different underlying pathology, such as Alzheimer disease (AD), can mimic its clinical course. The ultimate etiology of CBD is unknown; however, current neuropathological and genetic evidence support a role for microtubule-associated protein tau. The classic clinical presentation is corticobasal syndrome, which typically presents as an asymmetric parkinsonism with a variable combination of ideomotor apraxia, rigidity, myoclonus, and dystonia, often associated with the presence of an alien limb phenomenon. Recently, a new set of diagnostic criteria has been developed, but still definite diagnosis requires autopsy confirmation. At the present time, no disease modifying therapies are available, but extensive research is being conducted.
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