[Sympathetic nervous system, pain and epidural administration of morphine]

There are multilevel intrications between nociceptive afferences and sympathetic efferences: anatomical vicinity in visceral innervation; systemic and local activation of the sympathetic efferences in response to nociceptive stimulation; major role of sympathetic activation in the perpetuation of sympathetic dystrophies. The analysis of a retrospective series of 10 patients suffering from algodystrophia revealed that epidural morphine administration had a beneficial effect only in those which were treated at an early stage of their illness. Despite epidural morphine has been claimed to be without effect on the efferent sympathetic tone in normal animals and individuals, it seems that in some pathologic states, the sympathetic output can be depressed. Recent anatomical and neurophysiological evidences argue for such a possibility.