A team of scientists from Israel and Albania say they have found the primary source of phantom limb pain in nerves near the spine, according to the Israeli newspaper Haaretz. Their study was published online April 23 in the journal Pain, and will be in a forthcoming print issue.
There is currently a broad consensus among investigators that phantom limb pain is triggered by loss of sensory input and caused by maladaptive cortical plasticity. The scientists tested the alternative hypothesis that phantom limb pain is due not to the loss of input but rather to exaggerated input, generated in nerve fibers that used to innervate the limb. Thirty-one individuals with lower-limb loss were given the local anesthetic lidocaine, “near where their nerves from their amputated legs enter the spinal cord in the lower back,” according to the article in Haaretz. Within a short amount of time, the phantom limb pain and also nonpainful phantom limb sensation were temporarily eliminated or reduced. Control injections were ineffective, the team said. Given these results, they concluded that the primary drive of phantom limb pain is hyperexcitable sensory neurons rather than maladaptive cortical plasticity.