Asymmetric cortico-cortical inhibition in patients with progressive limb-kinetic apraxia

To evaluate the activity of cortico-cortical (intracortical) inhibitory circuits within the motor cortex in patients with progressive asymmetric limb-kinetic apraxia.We studied 4 patients with progressive limb-kinetic apraxia whose clinical diagnosis was corticobasal degeneration (CBD) and 7 control subjects. Cortico-cortical inhibition was measured using the technique of double pulse transcranial magnetic stimulation over the motor cortex. The effects of conditioning stimuli on the test responses were examined.In the normal control subjects, the conditioning magnetic stimulus suppressed motor evoked responses to the test stimulus at interstimulus intervals of 1 to 5 ms. This inhibition was significantly diminished on the affected side of the patients, but it was normal on the less affected side.Disruption of intracortical inhibitory circuits in the motor cortex may, at least in part, be related to severe limb clumsiness in the patients with progressive limb-kinetic apraxia.