Association of ideomotor apraxia with frontal gray matter volume loss in corticobasal syndrome

Objective: To determine the brain areas associated with specific components of ideomotor apraxia (IMA) in corticobasal syndrome (CBS). Design: Case-control and cross-sectional study. Participants: Forty-eight patients with CBS and 14 control subjects. Intervention: Administration of the Test of Oral and Limb Apraxia. Main Outcome Measures: Differences between patients with CBS and healthy controls and associations between areas of gray matter volume and IMA determined by voxel-based morphometry in patients with CBS. Results: Overall, IMA was associated with decreased gray matter volume in the left supplemental motor area, premotor cortex, and caudate nucleus of patients with CBS. The overall degree of apraxia was independent of the side of motor impairment. Praxis to imitation (vs command) was particularly impaired in the patients with CBS. Patients demonstrated equal impairment in transitive and intransitive praxis. Conclusions: In patients with CBS, IMA is associated with left posterior frontal cortical and subcortical volume loss. Despite showing left frontal volume loss associated with IMA, patients with CBS have particularly impaired imitation of gestures. These findings suggest either that the IMA of CBS affects a route of praxis that bypasses motor engrams or that motor engrams are affected but that they exist in areas other than the inferior parietal cortex.