Role of spinal noradrenergic system in transmission of pain in patients with spinal cord injury.

15 patients with deafferentation pain due to spinal cord injury were investigated for a spinal mechanism of pain transmission. Epidural morphine 5 mg in 5 ml of water had an analgesic effect in 5 patients, 3 of whom also had pain relief with epidural clonidine. Epidural clonidine 150 micrograms in 5 ml of saline had an analgesic effect in 7 patients who did not respond to epidural morphine. Neither epidural morphine nor clonidine was effective in the other 3 patients, 2 of whom obtained relief with epidural buprenorphine 0.3 mg in 5 ml of saline. 1 patient did not find relief with any of the injections. These data suggest that a spinal noradrenergic system may be as important as the opioid system in the transmission of pain in patients with spinal cord injury.