Study Finds Percutaneous PNS Provides Enduring Postamputation Pain Relief.
Percutaneous peripheral nerve stimulation was found safe and effective for treating chronic neuropathic postamputation pain up to 10 months after therapy, according to a study of 28 patients who underwent lower extremity amputation.
“This patient population is extremely underserved, given our current treatment modalities,” said principal investigator Christopher Gilmore, MD, a clinical assistant professor of anesthesiology at Wake Forest University Baptist Medical Center, in Winston-Salem, N.C.
Stimulation was provided by the SPRINT device (SPR Therapeutics), which Dr. Gilmore had implanted for postamputation, postsurgical and chronic low back pain in previous studies. “There is a natural kind of connection between the therapy and the underserved population,” he said.
A multicentre study recruited patients with a traumatic lower extremity amputation (Reg Anesth Pain Med 2019 Apr 5. pii: rapm-2018-100109). The average time since injury was 8.7 years, with an average of 7.0 years since the time of amputation. In total, 15 of the 28 patients (58%) had amputations above the knee. All patients underwent ultrasound-guided implantation of percutaneous peripheral nerve stimulation (PNS) leads and were then equally randomly assigned to receive either PNS (n=12) or placebo (n=14) for four weeks. Afterward, the placebo group crossed over, and all patients received PNS for an additional four weeks.
Seven of the 12 patients in the PNS group demonstrated at least a 50% reduction in average postamputation pain after four weeks of therapy, compared with two of 14 in the placebo group.
A significantly greater proportion of the PNS group (8/12) also reported at least a 50% reduction in pain and pain interference (Brief Pain Inventory) after eight weeks of therapy, compared with the proportion in the placebo group (2/14).
“We continue to follow up with these patients out to at least 12 months,” Dr. Gilmore said. “To date, four of five subjects (80%) from the PNS group who have completed their 12-month follow-up still had at least 50% pain relief after only eight weeks of therapy.”
Dr. Gilmore is surprised by the maintenance of effect. “Traditionally, one does not expect temporary neuromodulation to afford a subject pain relief for the long term,” he said. “But with this device, that has been the case in a number of previous studies. We believe there may be some modulation at the dorsal root ganglion, as well as at the level of the cord and higher centers, where there is downregulation of the chronicity and firing at those levels.”
Dr. Gilmore said the uptick in interest in PNS is supported by quality data. “We no longer need to use spinal cord stimulation devices and adapt them for use in the periphery,” he said. “Now we have devices that are ergonomically designed for use in the periphery. The SPRINT device, in particular, I think has an ideal and novel design behind it, with the microlead being 0.27 mm in diameter. The lead is also coiled, which allows for movement under the skin rather than pistoning through the skin.”
However, appropriate patient selection is key for effective peripheral PNS in the clinic, according to Dr. Gilmore, including those who will take care of the device, have realistic expectations of treatment, and do not have any other significant comorbid conditions that could cause infection or bleeding.
In addition, the procedure is fairly straightforward. “Anyone who is facile in the use of ultrasound for peripheral nerve blocks already possesses the skills necessary to perform this peripheral nerve stimulator placement,” Dr. Gilmore said.
Skin site reaction is the most frequently encountered side effect. “Otherwise, the treatment is tolerated pretty well,” Dr. Gilmore said. “In the study, there were some lead fractures under the skin. But we know that when these fractures occur, they are typically at the distal tip and happen upon the removal of the lead. These fractures have been tested and labeled as MRI-conditional in most cases.”
To enhance the safety of percutaneous PNS, Dr. Gilmore recommends a suitable sterile technique and a facility with ultrasound-guided procedures to identify the target structures and maintain sight of the needle tip at all times.
Dr. Gilmore expects the study’s findings about postamputation pain will be extrapolated to other neuropathic states, such as peripheral mononeuropathies, neuropathic pain after surgery, crush injuries and complex regional pain syndrome. “Although it remains to be seen whether we can generate evidence in those specific cases, our study gives promise that percutaneous PNS may be effective in a broader neuropathic pain population,” he said.
—Bob Kronemyer