HISTOPATHOLOGIC CHANGES IN PRIMATE SPINAL-CORD AFTER SINGLE AND REPEATED EPIDURAL PHENOL ADMINISTRATION

Background and Objectives. Epidural phenol for control of pain and spa sticity has been advocated for clinical use. This study determined the histopathologic changes that follow single and repeated epidural admi nistration of phenol in saline in nonhuman primates.Methods. Nine prim ates received 0.5 mL of either 3% phenol in saline (n = 4) or 6% pheno l in saline (n = 5) via lumbar epidural injection. Two additional prim ates received three consecutive daily epidural doses of 0.5 mL of 3% p henol in saline. Finally, 5 unoperated primates and 5 primates that re ceived only 2 mL, of radiographic contrast material served as control subjects. Two weeks after the epidural injection, spinal cords were re moved and processed for hislopathologic study by a neuropathologist bl inded to the solution administered.Results. None of the control animal s demonstrated histopathologic changes. One animal that received 6% ph enol died 3 days after injection. All phenol-treated animals demonstra ted predomi nantly posterior root damage. Spinal cord damage was seen in all animals receiving 6% phenol, in 2 animals receiving 3% phenol s ingle doses, and in neither animal receiving 3% phenol multiple doses. Anterior root damage occurred in all phenol-treated animals except th e 4 that received single 3% phenol injections. Animals that received 6 % phenol demonstrated greater lower extremity motor weakness than thos e in the other groups, but no clear correlation existed between extent of histopathologic changes and motor weakness. Conclusions. Motor wea kness, anterior root damage, and direct cord injury were noted in prim ates following epidural administration of phenol in concentrations bel ow what has been reported for clinical use in humans. Since it is more difficult to control the spread of epidural versus subarachnoid pheno l, the risks of epidural phenol may outweigh the benefits relative to subarachnoid administration.