Extended surround inhibition in idiopathic paroxysmal kinesigenic dyskinesia

Abstract

OBJECTIVE: Paroxysmal kinesigenic dyskinesia (PKD) is characterized by recurrent attacks of dyskinesia, in which movement of one body part produces involuntary movements of other body parts. Surround inhibition (SI), a mechanism for suppression of unwanted movements, could be deficient in these patients. To test this idea, we performed a transcranial magnetic stimulation (TMS) study in drug-naive patients with PKD.

METHODS: TMS was set to be triggered by self-initiated flexion of the index finger at different intervals. Average motor evoked potential (MEP) amplitudes obtained from self-triggered TMS were normalized to average MEPs of the control TMS at rest. Normalized MEP amplitudes of the patients' self-triggered TMS sessions at different intervals were compared to those of the controls.

RESULTS: During index finger flexion, MEP amplitudes from the little finger muscle were unchanged in both the patients and normal subjects, however, post-movement MEP enhancement observed in the normal subjects was absent in patients with PKD. These results suggest that the functional operation of SI is itself preserved, but that post-movement excitation of surrounding muscles is deficient in PKD.

CONCLUSIONS: This finding may represent that the operation of SI is extended to the post-movement period, perhaps as a compensatory mechanism for preventing unwanted movement in surrounding muscles.

SIGNIFICANCE: While many types of impaired inhibition have been described previously in PKD, this is the first possible example of increased inhibition.