Who May Benefit From On-Demand Control of Deep Brain Stimulation? Noninvasive Evaluation of Parkinson Patients

Background: In closed-loop on-demand control (ODC) of deep brain stimulation (DBS), stimulation is applied only when symptoms appear. Following stimulation of a fixed duration, DBS is switched off until the symptoms reappear. By repeating these demand-driven cycles, the amount of stimulation delivered can be decreased, thereby reducing DBS side-effects and improving battery-life of the pulse-generator. This article introduces R-o metric for quantification of degree of benefit of ODC and explores candidate selection in tremor-dominant Parkinson's disease (PD). Method: The study was performed on nine PD patients previously implanted with Medtronic DBS systems. Accelerometer sensor was placed on the tremor-dominant hand to detect onset of tremor. Fixed duration of stimulation (DS) of 20-80 sec was applied. Once the tremor was observed, stimulation was switched on. These trials were repeated during resting, postural, and kinetic conditions. R-o metric was calculated as the ratio of stimulation-off tremor-free period to the DS. R-o calculated at different DS were compared for each patient. Results: We found that for each patient, R-o varied with DS and an optimal DS* gave a higher percentage of stimulation-off time. Average R-o at DS* varied from 0.554 to 4.24 for eight patients giving 35%-80% stimulation-off time. Conclusions: R-o values can be used for selection of optimal DS* in ODC. Three of nine patients were found to be tremor-free without stimulation for >50% of total time with even up to 80% in one patient. Patients with low R-o may not benefit from ODC in DBS, where the trade-off between having side-effects and using ODC system will need to be assessed.