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Corticobasal ganglionic degeneration (CBGD) or corticobasal degeneration (CBD) is a pathological diagnosis in search of a nosological niche. It was originally described as corticodentatonigral degeneration by Rebeizet al,1 who recognised its relation to Pick's disease because of the focal cortical atrophy and the ballooned neurons (Pick cells). The clinical syndrome was first characterised by a combination of unilateral extrapyramidal signs and prominent apraxia, usually diagnosed in movement disorder clinics. “Alien hand,” vertical gaze palsy, and reflex myoclonus are frequent but non-obligatory signs. Both the clinical syndrome and the pathology were considered unique and well matched initially, but soon several descriptions of CBD pathology appeared, the clinical presentation of which was behavioural or aphasic, similar to the study of Mathuranath et al (this issue, pp304–312).2
The reverse also became evident. There have been several well described cases of the clinical corticobasal degeneration syndrome (CBDS) where the pathology turned out to be Pick's disease, or “dementia lacking distinctive histology”, or the “motor neuron type of frontotemporal dementia.” It also seems that the clinical syndrome of unilateral extrapyramidal symptoms, apraxia, and alien hand is more often accompanied by frontotemporal disinhibition dementia (FTD) and progressive aphasia (PA) than was previously thought.
Furthermore, if one follows up cases of FTD or primary PA, one eventually may encounter the development of typical CBDS, further underlying the relation of these syndromes clinically and pathologically. Mathuranath et al are doing a service to the neurological community by empha-sising the overlap of these conditions by their illustrative cases and thoughtful review of the literature. This clinical and pathological overlap led us to the concept of Pick complex, as Pick's disease is somewhat arbitrarily restricted to the specific pathology of Pick bodies by many neuropathologists.3 This concept received a substantial confirmation by the discovery of autosomal dominant families of FTD and parkinsonism linked to chromosome 174 and the numerous underlying tau mutations. Some of these families have a behaviour disorder resembling FTD, progressive language loss (PA), and parkinsonism (CBDS) represented in a single pedigree and the pathology ranges from CBD-like “Pick variants” to progressive supranuclear palsy within the same mutation.5
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