Limb apraxia and cognitive impairment in progressive supranuclear palsy.

Limb apraxia occurs in progressive supranuclear palsy (PSP); however, its characteristics and relation to dementia are unclear. We compared 25 probable PSP patients on cognitive and ideomotor apraxia tests with 19 healthy controls. Eleven PSP patients were demented (D-PSP) and 14 not (ND-PSP). D-PSP patients did worse than controls and ND-PSP patients in all cognitive tests; and ND-PSP patients did worse than controls in all except the memory test. In the apraxia test, PSP patients committed mainly sequence errors and executed complex gestures badly. Apraxia correlated strongly with dementia. In PSP, limb apraxia seems mainly due to frontal deafferentation and lesions, but only when these are severe enough to cause dementia.