Objective: To report the outcome of a novel interleaving stimulation (interlink-ILS) DBS programming paradigm (PP).

Background: DBS of the VIM is an effective treatment option for ET patients with medically refractory tremor. However, some patients may have sub-optimal tremor control when side effects (SE) prevent adequate current delivery. This can occur insidiously when worsening symptoms over time prompts increasingly higher current delivery, or when a lead is sub-optimally placed. The Activa DBS system has an ILS function which can potentially better shape the electrical stimulation field.

Methods: A low frequency PP was developed utilizing interlink-ILS. In this PP, two overlapping programs are created so that the overlapping area is focused around the optimal electrode contact. Consequently, this area receives conventional (high frequency) stimulation (CS) which allows for tremor reduction to be maintained, whereas the non-overlapping areas receive low frequency stimulation to reduce SE. Two ET patients (s/p bilateral VIM DBS) with a sub-optimal benefit-to-SE ratio on optimized CS settings were programmed with interlink-ILS. The clinical-rating-scale-for-tremor (TRS) was used to compare both PP (CS and interlink-ILS). We will report on six patients in this ongoing study.

Results: Case 1: 72-year-old female with incomplete LUE tremor suppression and SE (LLE heaviness, dysarthria) on CS (LVIM:9-8+,2.3V,170µs,190Hz) had interlink-ILS (LVIM1:9-11+,2.3V,160µs,125Hz; LVIM2:10-8+,2.4V,160µs,125Hz) implemented (maintained for 18 months). Tremor improved (TRS-Part-A: interlink-ILS-1, CS-2) and SE resolved.  

Case 2: A 66-year-old female with incomplete BUE tremor suppression and SE (gait instability, dysarthria) on CS (LVIM:1-3+,3.3V,60µs,130Hz;RVIM:0-2+,2.3V,60µs,130Hz) had interlink-ILS (LVIM1:1-3+,3.5V,90µs,65Hz;LVIM2:2-0+,3.8V,90µs,65Hz;RVIM1:0-2+,2.4V,90µs,65Hz;RVIM2:2-3+,2.4V,90µs,65Hz) implemented (maintained for 6 months). Tremor improved (TRS-Part-A: interlink-ILS-5, CS-7) and SE were reduced.

Conclusions: In these two cases, sub-optimally controlled tremor was improved with interlink-ILS. This may be owing to SE reduction, and therefore better benefit-SE profile, or because the two programs are delivering current in an alternating fashion at slightly different locations on the lead.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/a-novel-deep-brain-stimulation-programming-paradigm-for-essential-tremor/