Sensorimotor reorganization by proprioceptive training in musician's dystonia and writer's cramp

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Abstract
Objective: The sensorimotor organization (SMO) of the motor hand area is abnormal in focal hand dystonia and likely contributes to symptom manifestation. In healthy subjects SMO is changed by training with proprioceptive stimulation. Here we test whether similar interventions reverse the abnormal SMO in musician's dystonia and writer's cramp. If so, they could be developed for therapeutic application. Methods: In six non-musicians, six professional musicians, six patients with musician's dystonia, and six patients with writer's cramp, SMO was explored by measuring changes in short-interval-intracortical-inhibition (SICI) during short periods of hand muscle vibration before and after two training types: AttVIB, involving attention to 15 minutes vibration of the abductor pollicis brevis (APB); and AttIndex, involving attention to subtle cutaneous stimulation of the index finger. Results: In healthy non-musicians, baseline SMO is spatially differentiated: SICI is reduced in projections to the vibrated, but enhanced to the non-vibrated muscles. Here AttVIB increased and AttIndex reduced the effect of subsequent APB-vibration on SMO. In healthy musicians, baseline SMO is less differentiated. AttVIB reinstated a more differential SMO pattern while AttIndex attenuated the effect of APB vibration. In focal hand dystonia, SMO is completely dedifferentiated. AttVIB tended to restore a more differential SMO in musician's dystonia but not in writer's cramp while AttIndex failed to induce any changes in both groups. Conclusion: The intervention effect depends on the pre-interventional sensorimotor organization (SMO). In focal hand dystonia, particularly in musician's dystonia, it is possible to retrain an abnormal SMO toward a more differential pattern, which has potential implications for therapy.