Failure of long-term nerve root stimulation to improve neuropathic pain

Object. Stimulation of dorsal nerve roots or dorsal root ganglia was reported to alleviate neuropathic pain in selected patients during the early postoperative period. A prospective study was initiated to investigate long-term outcome in patients with neuropathic pain of the lower extremities or groin who were treated with selective nerve root stimulation. Methods. The study included patients with dermatomally distributed neuropathic pain who were > 18 years of age and in whom the pain was refractory to medical treatment. The patients were prospectively evaluated using a visual analog scale (VAS) for pain and ratings for quality of life, activities of daily living, and depression preoperatively, and after defined intervals postoperatively. Implantation of electrodes was performed via foraminotomy or interlaminar fenestration in an awake procedure. An implantable pulse generator (IPG) was implanted in a second operation after successful test stimulation performed over several days. Results. Three patients were included in the study before it was stopped. The mean maximum pain score preoperatively was 9.3. All patients had successful test stimulation with > 50% pain relief prior to implantation of the IPG (mean maximum VAS Score 3.6). The beneficial effect, however, was lost within the next few months despite adjustment of stimulation settings. With higher amplitudes, side effects such as pain attacks or motor phenomena occurred. They disappeared after stopping stimulation, but neuropathic pain recurred to its full extent. The study was stopped 18 months after the first implantation, when the third and last IPG of this series was explanted. Due to the overall short-term effect of stimulation, no relevant changes in ratings for quality of life, activities of daily living, or depression were detected. Conclusions. Spinal nerve root stimulation proved to be effective on short-term follow-up in 3 patients with neuropathic pain in a dermatomal distribution. Long-term stimulation, however, was disappointing because of the loss of effectiveness and the occurrence of side effects.