Bilateral GPi DBS is useful to reduce abnormal involuntary movements in advanced Parkinson's disease patients, but its action is related to modality and site of stimulation

In Parkinson's disease (PD) patients, internal globus pallidus (GPi) stimulation has been reported to produce good effects on abnormal involuntary movements (AIM); less improvement has been observed in extrapyramidal symptoms. We assessed the effect of monopolar dorsal (uppermost), ventral (lowest) and bipolar (uppermost vs. lowest) bilateral globus pallidus stimulation by quadripolar electrode on extrapyramidal symptoms and AIM induced by a dose of apomorphine. Six PD patients were studied in OFF therapy condition after surgery without stimulation (STIM OFF) and during stimulation (STIM ON) with the three different modalities. All patients were evaluated by the unified Parkinson's disease rating scale, section III (UPDRS) and by the AIM. Our results show that all three bilateral GPi stimulation modalities reduce the UPDRS score (between 49.7 and 31.5%), although the bipolar and lowest stimulation are the most effective. Similarly, bipolar and lowest stimulation were also the most effective in reducing the occurrence and intensity of the apomorphine-induced AIM. On the contrary, uppermost stimulation (UP ON) produced an AIM occurrence similar to that observed in the OFF stimulus condition. We suggest that bilateral GPi stimulation is an useful procedure to ameliorate extrapyramidal signs of advanced PD patients; however, it produces an antidyskinetic effect only if the ventral or the entire GPi is stimulated. On the contrary, the UP ON, most probably located in the external globus pallidus (GPe), does not modify the AIM occurrence.