Control of simultaneous movements distinguishes depressive motor retardation from Parkinson's disease and neuroleptic parkinsonism.

Patients with depressive motor retardation, neuroleptic induced parkinsonism or Parkinson's disease were tested on movement tasks requiring control of simultaneous movements. This was in order to determine whether these three groups of patients, who all show slowing of movements, also share the distinctive impairment of simultaneous movement control that is observed in Parkinson's disease. Though all three patient groups showed equivalent slowing on the motor tasks that were studied, the patterns of impairment were different. Only the patients with parkinsonism, either neuroleptic induced or from Parkinson's disease, showed additional slowing of a rapid ballistic elbow flexion movement when it was performed simultaneously with a rapid squeeze of the ipsilateral hand. Only patients with parkinsonism showed a significant increase in dual task interference on a bimanual bead and tapper task, compared with controls. The bead and tapper interference in patients with depressive motor retardation was between that of controls and parkinsonism. Having a bimanual skill had a large effect on the subjects' dual task interference on this task. The measures of dual task interference for the two tasks did not correlate with one another; difficulty running simultaneous motor programs does therefore not explain the interference that is observed when tapping is performed while the other hand simultaneously performs a dextrous motor task. Only patients with parkinsonism showed increased fatigue on the tapping task. The patients with depressive motor retardation did have elevated scores on a clinical rating of parkinsonism. Nevertheless there are clearly defined differences between the movement disorder observed in patients with depression, and that observed in in parkinsonism. The patterns of impairments in patients with neuroleptic parkinsonism were very similar to those of Parkinson's disease.