Corticobasal degeneration as a cognitive disorder.

The presence of cognitive impairment in corticobasal degeneration (CBD) is now widely recognised. Our review of the literature reveals that, although the pattern and severity of neuropsychological impairments can be highly variable across patients, several general trends can be identified. The most characteristic impairments are limb apraxia (usually ideomotor), constructional and visuospatial difficulties, acalculia, frontal dysfunction, and nonfluent aphasia. The limb apraxia is associated with deficits in drawing, copying, and handwriting, but there is emerging evidence that the problems with handwriting are not due exclusively to the apraxia. The findings with respect to episodic memory are more variable, but when there is impairment in this area, it tends to be milder than that seen in Alzheimer's disease. Semantic memory functioning appears relatively preserved but has been poorly studied. Problems with speech are common, and may be due to dysarthria or buccofacial apraxia. Aphasia, although initially considered rare, is in fact a common accompaniment of CBD, may be the presenting feature, and is typically nonfluent in type. More systematic investigation of the clinical and neuropathological overlap between progressive nonfluent aphasia (generally considered to be a form of frontotemporal dementia) and CBD is needed.