Intrathecal morphine's effect on somatosensory impulses transmission-studied with posterior tibial nerve SSEP

In order to investigate neurotoxic potential of spinally injected morphine solution, somatosensory evoked potential (SSEP) was utilized to detect the change of electrophysiologic activity of spinal neurons after long term application of intrathecal morphine. Eight patients received intrathecal morphine injection regularly after CHEMO-PORT implantation were studied with posterior tibial nerve SSEP. Patients received SSEP examination just before and right after first episode of morphine injection and were followed up at 30 minutes, 60 minutes, 2 hours, 8 hours, and the 7th day and the third month of regularly injection. The results showed that there were no definite change of latencies and amplitudes of impulses generated by lumbar spinal cord (N22) and cortex (P40). We therefore suggest that electrophysiologic activities of spinal cord and cortex are not affected by chronic intrathecal morphine injection. Possible mechanism and proposed pathway of morphine's action were also discussed.