A disturbance in the control of muscle force in neuroleptic-naive schizophrenic patients.

The voluntary motor disturbances found among many schizophrenic patients consist of motor incoordination, disturbed pursuit tracking, difficulty following movement sequences, desynchronized tapping, and a myriad of neurologic soft signs. The problem with many of these observations is that it is extremely difficult to distinguish movement disorders related to neuroleptic treatment from those that may have occurred spontaneously. The aim of the present study was to examine potential disturbances in the voluntary control of steady-state force in neuroleptic-naive schizophrenic patients and normal comparison subjects. Twenty-one patients and 21 age- and gender-matched comparison subjects were studied. Spectral analyses of hand force instability revealed a significant difference between patients and comparison subjects. In 52 of the patients, the disturbance in the control of force exceeded the 95th percentile of the comparison mean. Degree of force instability was correlated with positive but not negative symptoms of schizophrenia. These findings suggest that schizophrenic patients may exhibit a disturbance in the control of muscle force that cannot be attributed to the neuroleptic effects of antipsychotic medication. The pattern of disruption, characterized by abnormal spectral energy within the 1.5 to 3.0 Hz range, suggests a motor disturbance that resembles tardive dyskinesia. Implicit within these findings of neuroleptic naive patients is the possibility that disturbances in the control of isometric force may represent spontaneous dyskinesia.