Early this year, we wrote about how peripheral nerve stimulation (PNS) can help control amputation-related pain. PNS is known to relieve chronic pain by sending electrical impulses to the affected nerves. While the technology is not touted as a treatment for phantom limb pain, the connection is evident. To further explore this connection, two major initiatives are underway to test the potential of PNS for relieving phantom limb pain, and the early results are pretty hopeful.
Determining PNS's effect on new amputees
Current evidence that proves PNS's effect on amputation-related pain is still in the early stages. However, this is changing, and in 2019, the U.S. Veterans Administration (VA) launched a pilot study to track pain in the first year following amputation.
A preliminary report shows that 75% of the subjects treated with the Sprint PNS system experienced substantially less pain than the control group during the first eight weeks after amputation. According to the lead investigator on the study, Denise Lester M.D., the first eight weeks is a critical time to control or minimize phantom limb pain.
Generally, people with high post-operative pain are at greater risk of developing persistent pain. Implementing PNS immediately after amputation may help short-circuit the establishment of pain-causing neural pathways. This is because PNS operates almost like a pacemaker—it threads tiny electrodes under the skin and pulses rhythmically, which drowns out erratic neurological signals.
In effect, PNS retrains the nerves before they develop patterns associated with phantom limb pain. Furthermore, Lester says that the immediate implementation of PNS can prepare patients to be fitted for a prosthesis as early as two months after amputation.
With the pilot showing promising results, a more extensive study may begin soon.
PNS technology for amputees
Existing PNS technology is not explicitly designed for phantom limb pain, but that will soon change. Researchers at Ripple Neuro are currently working on the second initiative, which will see PNS technology specifically for amputees. The Utah-based company recently received a $2 million grant from the National Institute of Health's HEAL Initiative to work on the new technology.
According to Ripple Neuro's chief scientific officer Daniel McDonnall, the goal of the study is to restore the natural signals that the central nervous system is designed to receive from the limb.
This study will see a "next-generation device" that will reduce phantom limb pain and provide sensory input from the prosthesis. The device is designed to relay information about position, contact, and force from the prosthesis to the brain through implantable PNS electrodes. This will establish direct communication between the brain and the prosthesis, stimulating familiar neurological patterns that existed before amputation.
By re-establishing these old patterns, Ripple Neuro's device would diminish the development of dysfunctional pathways that cause phantom limb pain.As of this writing, the technology is still in the early phases. Clinical trials will likely begin in early 2022.