Treating Chronic, Intractable Pain with a Miniaturized Spinal Cord Stimulation System: 1-Year Outcomes from the AUS-nPower Study During the COVID-19 Pandemic

Abstract

Purpose: Spinal cord stimulation (SCS) is a highly effective treatment for chronic neuropathic pain. Despite recent advances in technology, treatment gaps remain. A small SCS system with a miniaturized implantable pulse generator (micro-IPG; <1.5 cm3 in volume) and an externally worn power source may be preferred by patients who do not want a large, implanted battery. We report here the long-term outcomes from the first-in-human study evaluating the safety and performance of a new neurostimulation system. Patients and Methods: This was a prospective, multi-center, open-label, single-arm study to evaluate this SCS system, in the treatment of chronic, intractable leg and low-back pain. Consented subjects who passed screening continued on to the long-term phase of the study. One-year, patient-reported outcomes (PRO’s) such as pain (Numeric Rating Scale, NRS), functional disability, quality of life, and mood were captured. Results: Twenty-six (26) evaluable subjects with permanent implants were included in this analysis. The average leg pain NRS score decreased from 6.8 ± 1.2 at baseline to 1.1 ± 1.2 at the end of the study (p < 0.001), while the average low-back pain NRS score decreased from 6.8 ± 1.2 to 1.5 ± 1.2 (p < 0.001). The responder rate (proportion with ≥50% pain relief) was 91% in the leg(s) and 82% in the low back. There were significant improvements in functional disability (Oswestry Disability Index) and in mood (Beck Depression Inventory), demonstrating a 46% and 62% improvement, respectively (p < 0.001). Eleven-point Likert scales demonstrated the wearable to be very comfortable and very easy to use. Conclusion: There were considerable challenges conducting a clinical study during the COVID-19 pandemic, such as missed study programming visits. Nevertheless, subjects had significant PRO improvements through 1-year. The small size of the implanted device, along with a proprietary waveform, may allow for improved SCS outcomes and a drop in incidence of IPG-pocket pain. Plain Language Summary: Chronic neuropathic pain of the low back and legs is a common affliction. Unfortunately, many of these cases are medically intractable and require more invasive treatments. One such treatment is spinal cord stimulation, in which very small, cylindrical electrodes (leads) are percutaneously introduced into the epidural space where they deliver mild electrical pulses to the spinal cord thereby blocking the pain signals from reaching the brain. Among the shortcomings of this general approach is the bulkiness of the implanted battery and electronics that power the electrodes, which can be as large as 44 cm3 in volume. We report here the results of a study employing a very small spinal cord stimulator implant (<1.5 cm3 in volume) that is externally powered by a wearable device. The results of this multi-center, prospective, open-label, single-arm study are reported here. Following 1 year of spinal cord stimulation therapy, the average pain reduction was 79% in the legs and 81% in the back, both of which were statistically significant at the p<0.001 level. At the same study endpoint, patient-reported outcomes demonstrated significant improvements in functional disability (p < 0.001) and mood (p < 0.05). These outcomes are comparable to many of the other larger, fully implantable systems.