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

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).

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.

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.

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.