Neuromodulation for Post-amputation Pain
By Paul Lynch, MD, Tory McJunkin, MD, Andrew Wallmann, BS, & Edward Swing, PhD
Dear Arizona Pain Specialists,
Some of my patients suffer from chronic pain after limb amputations. I have considered treating their pain with neuromodulation devices, but I am not sure if such treatments are effective for this type of pain. Is neuromodulation an appropriate treatment for post-amputation pain?
Missing Pain Relief
Dear Missing Pain Relief,
Historically, post-amputation pain has been notoriously difficult to manage. Considering the prevalence of pain after amputation, sometimes reported as high as 95%1, it is an area that merits increasing attention. It is important to classify what type of post-amputation pain the patient is experiencing, as the best treatments may differ depending on the underlying mechanism. Broadly, the pain can be categorized as either residual limb pain (RLP), also known as stump pain, or phantom limb pain (PLP). Neuromodulation treatments for pain include peripheral nerve stimulation (PNS), spinal cord stimulation (SCS) and transcutaneous electrical nerve stimulation (TENS).
Examining the evidence
Few studies have examined the use of PNS for either RLP or PLP. There is some evidence suggesting PNS may be a viable option for the treatment of RLP. Previously, the use of PNS for post-amputation pain has been limited due to the surgically invasive nature of the procedure and the necessity of precise lead placement. A recent case study found that percutaneous and remote placement of the lead resulted in 60% reduction in self-reported RLP at the end of a two-week home trial2. A lead was placed remotely (>1cm from the femoral nerve). Stimulation was continued for two weeks, during which the patient experienced a 60% reduction in self-reported pain. Though this evidence is promising, particularly given relief without close proximity to the nerve, it is limited in that only a single episode of RLP was examined. This patient also rarely experience PLP, leaving the efficacy of PNS for PLP unclear.
Similarly, spinal cord stimulation has been shown to have sustainable benefits in some patients with amputation related pain, though results have been variable3-5. In a recent study, 10 out of 12 patients experienced worthwhile benefits. Though the amount of pain relief varied, the mean pain reduction was 65%4. A “worthwhile benefit” in this study was determined by the patients self-reporting that their pain reduction was meaningful and worthwhile. In all of these patients, quadripolar paddle electrodes were implanted epidurally by laminectomy and stimulator parameters were adjusted to fit the patient. Patients then reported their benefit as a percentage of pain relief at subsequent follow up visits. Interestingly, patients experiencing PLP reported relief in the phantom limb as well as the residual limb, but only if the sensation of the stimulation proceeded past the stump and into the phantom limb.
These studies indicate that PNS and SCS may be a viable option for patients where alternative treatment modalities have failed, but the lack of randomized control trials determining the efficacy of this treatment make it difficult to conclusively recommend either procedure6.
Whereas peripheral neuromodulation may be sufficient for RLP, it is widely believed that PLP is due to supraspinal mechanisms6. Based on this reasoning, treatments such as the motor and parietal cortex stimulation, rather than stimulation of the spinal or peripheral nerves, have been seen as the most intuitive treatment option.7 However, a recent pilot study found that TENS provided both RLP and PLP relief.8 This study examined ten individuals with transtibial amputations and persistent moderate-to-severe PLP or RLP. The effect of TENS on the patients’ pain was then observed both at rest and with movement. Following 60 minutes of TENS therapy, the mean reduction in pain with movement was 3.9 on a numerical rating scale of 0 to 10. Again, the lack of more rigorous evidence prevents any conclusive recommendation from being made concerning TENS therapy for PLP, but this study found promising results that merit additional research.
The various forms of neuromodulation have the potential to treat both RLP and PLP, but the evidence is currently limited by small sample sizes and the lack of control groups. More studies, including randomized control trials are needed to provide stronger conclusions regarding the effectiveness of these therapies. Nonetheless, the promising results observed so far suggest the potential for neuromodulation treatments to relieve post-amputation pain, including both residual limb pain and phantom limb pain.
Dr. Lynch and Dr. McJunkin own and operate Arizona Pain Specialists, a comprehensive pain management practice that provides minimally invasive, clinically proven treatments, with three locations in the greater Phoenix area. Dr. Lynch and Dr. McJunkin also provide consulting services to other pain doctors around the country through their partner company, Boost Medical. For more information, visit ArizonaPain.com and BoostMedical.com.
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