Prehension is an ideationally simple, cued Movement requiring proximal (transport) and distal (manipulation) limb control. Patients with this syndrome of progressive apraxia are unable to perform many activities of daily living that require prehension. There is little known about how this syndrome kinematically disrupts such movements or whether concurrent dementia might play a critical role.
Using prehension as a paradigm for an ideationally simple, cued functional movement, we sought to (1) characterize the kinematic features of progressive apraxia in general, and (2) contrast the kinematic differences between apraxic patients with and without dementia.
Eight patients with the syndrome of progressive apraxia (including five without dementia, one of whom had autopsy-confirmed corticobasal ganglionic degeneration, and three with dementia, one of whom had autopsy-confirmed Alzheimer's disease) were compared with eight age-matched normal control subjects on a prehension task using an Optotrak camera system.
Compared with control subjects, apraxic subjects had slowed reaction time, slowed transport and manipulation kinematics, greater lateral deviation from the linear prehension trajectory, greater intermanual asymmetry, motor programming disturbances, and mild transport-manipulation uncoupling. There were minor differences between the apraxia subgroups such as greater intermanual differences and impaired grip aperture velocity in the nondemented group, and overall slower movement in the demented group.
There are major kinematic differences between apraxic and control subjects on a prehension task. The differences between clinical-pathologic subgroups are more subtle, and the movement disorder itself rather than concurrent dementia is the greatest determinant of motor disability.