Alteration of sensorimotor integration in musician's cramp: impaired focusing of proprioception

Objective: The influence of muscle vibration (MV) as a strong proprioceptiv e input on motorcortical excitability was studied in 5 patients with musici an's cramp, 5 musician controls and 5 non-musician controls Methods: The relaxed flexor carpi radialis (FCR), involved in the dystonic movement in all patients, was vibrated using low frequency (80 Hz) and low amplitude (0.5 mm). Transcranial magnetic stimulation (TMS; intensity, 120% of motor threshold) was applied without MV, 3 and 9 s after the onset of M V. Motor-evoked potentials (MEPs) in the FCR and in the antagonistic extens or carpi radialis (ECR) were recorded. Results: With MV, musician and non-musician controls showed a facilitation of MEPs in the FCR and a decrease of MEPs in the ECR. In musician's cramp, both phenomena were significantly less pronounced. Conclusions: The reduced facilitation of MEPs in musician's cramp indicates a reduced MV-induced activation of motorcortical areas representing the FC R. The less pronounced inhibition by MV reflects a reduced inhibitory contr ol of the antagonistic ECR. As there were no differences between musician a nd non-musician controls, the observed changes in musician's cramp refer to this special form of focal dystonia. An impairment of focused motorcortica l activation by proprioceptive input from a muscle involved in the dystonic movement is suggested. (C) 2000 Elsevier Science Ireland Ltd. All rights r eserved.