Limb apraxia in corticobasal degeneration and progressive supranuclear palsy

Objective: Corticobasal degeneration (CBD) and progressive supranuclear palsy (PSP) share pathologic features, and cortical and subcortical signs. Apraxia is frequently described in CBD and sometimes in PSP; however, it is difficult to distinguish ideomotor from limb-kinetic apraxia, and apraxia frequency is unclear. The authors set out to clarify the nature and frequency of apraxia in these diseases. Methods: The authors compared probable CBD and PSP patients, matched for motor disability, to healthy age-matched controls on cognitive tests and the De Renzi ideomotor apraxia test. Results: Cognitive impairment was similar, but more CBD (70.8%) than PSP (36%) patients had apraxia. CBD patients committed more apraxic errors of awkwardness and were more compromised on simple gestures; PSP patients committed more sequence errors. Conclusions: While progressive supranuclear palsy ( PSP) patients had ideomotor apraxia, the peculiar gesture compromise in corticobasal degeneration (CBD) suggests that limb-kinetic apraxia is dominant. In both illnesses, the movement production system of Roy and Square appears compromised: in CBD defective control of muscle activation seems likely, producing clumsy movements; in PSP, control of motor program activation appears defective, resulting in sequence errors and perseverations. The De Renzi test can reliably estimate apraxia frequency and may be used to distinguish limb-kinetic from ideomotor apraxia.