THE NATURE OF APRAXIA IN CORTICOBASAL DEGENERATION

Although apraxia is one of the most frequent signs in corticobasal deg eneration, the phenomenology of this disorder has not been formally ex amined. Hence 10 patients with corticobasal degeneration were studied with a standardised evaluation for different types of apraxia. To mini mise the confounding effects of the primary motor disorder, apraxia wa s assessed in the least affected limb. Whereas none of the patients sh owed buccofacial apraxia, seven showed deficits on tests of ideomotor apraxia and movement imitation, four on tests of sequential arm moveme nts (all of whom had ideomotor apraxia), and three on tests of ideatio nal apraxia (all of whom had ideomotor apraxia). Ideomotor apraxia sig nificantly correlated with deficit in both the mini mental state exami nation and in a task sensitive to frontal lobe dysfunction (picture ar rangement). Two of the three patients with ideomotor apraxia and ideat ional apraxia showed severe cognitive impairments. The alien limb beha viour was present only in patients with ideomotor apraxia. In conclusi on, ideomotor apraxia is the most frequent type of apraxia in corticob asal degeneration, and may be due to dysfunction of the supplementary motor area. There is a subgroup of patients with corticobasal (ideomot or and ideational apraxia), which correlates with global cognitive imp airment, and may result from additional parietal or diffuse cortical d amage.