Variance in effects of subthalamic nucleus stimulation

: Chronic stimulation of subthalamus nucleus (STN) is effective in treating severe motor fluctuation and levodopa induced dyskinesia as well as parkinsonian motor symptoms. The improvement of peak-dose/diphasic dyskinesias of STN stimulation is considered to be due to the decrease in the daily dosage of antiparkinsonian drugs. However one report pointed out that STN stimulation improved directly levodopa induced dyskinesia. Moreover the timing of the improvement for levodopa induced dyskinesia is not yet obvious. In the present study, we have assessed variance in the latency of improvement of levodopa induced dyskinesia due to STN stimulation. In addition, we would clarify an issue which cite of STN stimulation improved parkinsonian symptoms and motor complication (motor dyskinesias and motor fluctuation). We have studied seven patients diagnosed with advanced idiopathic Parkinson's disease with motor fluctuations and levodopa induced dyskinesias. Before and after the implantation of stimulating electrode, patients were assessed by the Unified Parkinson's Disease Rating Scale and % 'OFF' motor state. The dosage of the antiparkinsonian medication was not modified for one month prior to implantation. Following implantation, dosage of the medication and strength of stimulation was adjusted, if necessary. Symptoms of motor fluctuation and dyskinesia improved in all patients six month after surgery. The mean off-time duration and dyskinesia disability improved compared with presurgical conditions. However, the time course of the improvement of dyskinesias was not the same among patients. Contralateral limb dyskinesias in three patients improved immediately after the stimulation without modification of medication. In contrast, the stimulation worsened contralateral limb dyskinesias in other three patients immediately following the surgery. In two of the three patients, dyskinesias gradually improved within one month after surgery without reducing the dosage of medication. Dyskinesias of the other patient improved following a reduction in the dosage of medication one month after the surgery. Improvement of parkinsonian symptoms of the patients with longer latency of stimulation effect for dyskinesias was better than that of the patients with shorter latency. Stimulation cite of the former group appeared to locate more central than that of the latter group. Latency and strength of the effects of STN stimulation are variable.