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

To evaluate the activity of cortico cortical (intracortical) inhibitory cir cuits within the motor cortex in patients with progressive asymmetric limb- kinetic apraxia. Materials and methods - We studied 4 patients with progres sive limb-kinetic apraxia whose clinical diagnosis was corticobasal degener ation (CBD) and 7 control subjects. Corticocortical inhibition was measured using the technique of double pulse transcranial magnetic stimulation over the motor cortex. The effects of conditioning stimuli on the test response s were examined. Results - In the normal control subjects, the conditioning magnetic stimulus suppressed motor evoked responses to the test stimulus a t interstimulus intervals of 1 to 5 ms. This inhibition was significantly d iminished on the affected side of the patients, but it was normal on the le ss affected side. Conclusion - Disruption of intracortical inhibitory circu its in the motor cortex may, at least in part, be related to severe limb cl umsiness in the patients with progressive limb-kinetic apraxia.