Deafferentation pain resulting from cervical posterior rhizotomy is alleviated by chromaffin cell transplants into the rat spinal subarachnoid space

OBJECTIVE: Deafferentation pain is common after posttraumatic brachial plexus avulsion in humans. Alleviation of such pain is poorly achieved by most therapeutic interventions; the only efficient neurosurgical procedure currently available is lesioning of the dorsal root entry zone. Previous work has demonstrated that adrenal medullary transplants into the lumbar spinal subarachnoid space can alleviate neuropathic pain behavior resulting from peripheral nerve or spinal cord injury. The purpose of this study was to evaluate the potential effects of adrenal medullary transplants on brachial plexus deafferentation pain. METHODS: The cervical posterior rhizotomy model was selected as an upper segmental deafferentation model because it mimics the pathological situation after traumatic brachial plexus avulsion in humans. Animals underwent a right posterior cervical rhizotomy extending from C5 to T1 and received either adrenal medullary transplants or control striated muscle transplants into the cervical subarachnoid space. The clinical evolution was evaluated daily for self-directed behaviors indicative of ongoing pain, including onset, dermatomal extent, and severity. RESULTS: In animals with muscle control transplants, self-directed behaviors appeared in 83.3% of the group, with a mean delay between rhizotomy and onset of self-directed behaviors of 8 days. In contrast, only 30.8% of the animals implanted with chromaffin cells exhibited any signs of self-directed behaviors, and these had a mean onset delay of 14 days. CONCLUSION: The suppression of self-directed behaviors by adrenal medullary transplants is similar to that observed after dorsal root entry zone lesioning and suggests that this approach may offer a nonablative alternative in the management of deafferentation pain resulting from dorsal root avulsion.