Treating Phantom Limb Pain Using Continuous Peripheral Nerve Blocks: A Department of Defense Funded Multicenter Study
When a limb is traumatically severed, pain perceived in the part of the body that no longer exists often develops. This is called "phantom limb" pain, and is different from "stump" pain, which is pain within the part of the limb that remains intact. Unfortunately, phantom pain resolves in only 16% of people, with the rest experiencing this pain for the remainder of the lives. There is currently no reliable treatment for phantom limb pain. The exact reason that phantom limb pain occurs is unclear, but when a nerve is cut—as happens with a traumatic amputation—changes occur in the brain and spinal cord that actually worsen with increasing phantom pain. These abnormal changes may often be corrected by putting local anesthetic—termed a "peripheral nerve block"—on the injured nerve, keeping any "bad signals" from reaching the brain, with resolution of the phantom limb pain. However, when the nerve block ends after a few hours, the phantom pain returns. But, this demonstrates that the brain abnormalities—and phantom pain—that occur with an amputation may be dependent upon the "bad" signals being sent from the injured nerve(s), suggesting that a very long peripheral nerve block—lasting many days rather than hours—may permanently reverse the abnormal changes in the brain, and provide lasting relief from phantom pain. Until recently, extending a peripheral nerve block beyond 16 hours was unrealistic. However, a treatment option called a "continuous peripheral nerve block" is now available. This technique involves the placement of a tiny tube—smaller than a piece of spaghetti—through the skin and next to the nerves supplying the amputated limb. The tiny tube may be placed with minimal discomfort in about 15 minutes. Numbing medicine called local anesthetic is then infused through the tube, blocking any signals that the injured nerve sends to the spinal cord and brain. Using a small, portable infusion pump, this prolonged nerve block may be provided in individuals' own homes. The ultimate objective of the proposed research study is to determine if a 6-day continuous peripheral nerve block provided at home is an effective treatment for persistent phantom limb pain following a traumatic limb amputation. The primary hypothesis (what the researchers predict) is that phantom limb pain intensity will be significantly decreased 4 weeks following treatment with a 6-day continuous peripheral nerve block.