Objectives: To evaluate the activity of cortico-cortical (intracortical) inhibitory circuits within the motor cortex in patients with progressive asymmetric limb-kinetic apraxia.
Materials and methods: 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.
Results: 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.
Conclusion: 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.