Phantom Limb clinical trials at UCSD

When a limb is severed, pain perceived in the part of the body that no longer exists often develops and is called "phantom limb" pain. Unfortunately, phantom pain goes away in only 16% of afflicted individuals, and there is currently no reliable definitive treatment. The exact reason that phantom limb pain occurs is unclear, but when a nerve is cut-as happens with an amputation-changes occur in the brain and spinal cord that actually increase with worsening phantom pain. These abnormal changes may often be corrected by putting local anesthetic-called a "nerve block"-on the injured nerve, effectively keeping any "bad signals" from reaching the brain with a simultaneous resolution of the phantom limb pain. However, when the nerve block resolves after a few hours, the phantom pain returns. But, this demonstrates that the brain abnormalities-and phantom pain-that occur with an amputation are not necessarily fixed, and may be dependent upon the "bad" signals being sent from the injured nerve(s), suggesting that a very long peripheral nerve block-lasting many months rather than hours-may permanently reverse the abnormal changes in the brain, and provide definitive relief from phantom pain. A prolonged nerve block lasting a few months may be provided by freezing the nerve using a process called "cryoneurolysis". The ultimate objective of the proposed research study is to determine if cryoanalgesia is an effective treatment for intractable post-amputation phantom limb pain. The proposed pilot study will include subjects with an existing above-knee amputation who experience intractable daily phantom limb pain. A single ultrasound-guided treatment of cryoneurolysis (or sham block-determined randomly like a flip of a coin) will be applied to the major nerves of the thigh. Although not required, each subject may return 4-6 months later for the alternative treatment (if the first treatment is sham, then the second treatment would be cryoneurolysis) so that all participants have the option of receiving the active treatment. Subjects will be followed for a total of 12 months with data collected by telephone.

When a limb is amputated, pain perceived in the part of the body that no longer exists often develops, called "phantom limb" pain. The exact reason that phantom limb pain occurs is unclear, but when a nerve is cut-as happens with an amputation-changes occur in the brain and spinal cord that are associated with persistent pain. The negative feedback-loop between the injured limb and the brain can be stopped by putting local anesthetic-called a "nerve block"-on the injured nerve, effectively keeping any "bad signals" from reaching the brain. A "continuous peripheral nerve block" (CPNB) is a technique providing pain relief that involves inserting a tiny tube-smaller than a piece of spaghetti-through the skin and next to the target nerve. Local anesthetic is then introduced through the tiny tube, which bathes the nerve in the numbing medicine. This provides a multiple-day block that provides opioid-free pain control with no systemic side effects, and may prevent the destructive feedback loop that results in phantom limb pain following an amputation. We propose a multicenter, randomized, triple-masked (investigators, subjects, statisticians), placebo-controlled, parallel arm, human-subjects clinical trial to determine if a prolonged, high-concentration (dense), perioperative CPNB improves post-amputation physical and emotional functioning while decreasing opioid consumption, primarily by preventing chronic phantom limb pain.