Volitional control of involuntary movements.

Voluntary suppressibility of abnormal movements is helpful in the classification of movement disorders because this ability appears to be a common component of tics. However, there has been no systematic study of voluntary suppressibility in other movement disorders. We have therefore assessed 146 patients with tremors and dyskinetic disorders as to their ability to suppress movements by mental concentration. Patients were videotaped while trying to stop their movements, and the length of time they could suppress their abnormal movements was recorded. One hundred percent (10 of 10) of patients with tics could suppress movements for an average of 2.5 min. Two percent (1 of 50) of essential tremor patients could suppress the tremor, and the tremor of 24% (12 of 50) was made worse by mental concentration. Eighty percent (4 of 5) of neuroleptic-induced tremor could be improved mentally. Seventy percent (35 of 50) of patients with parkinsonian tremor could voluntarily diminish their tremor for an average of 48 s. Fifty percent (8 of 16) of chorea (tardive dyskinesia, Huntington's disease, postencephalitic) was reduced. Dystonia was suppressible in 20% (3 of 15). It is concluded that movement disorders besides tics can be voluntarily suppressed and that suppressibility should not be used to classify movement disorders. Tics, however, are easier to suppress and can be suppressed for a longer time.