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.