Spinal opiate analgesia and facial pruritus: a neural theory.

Facial pruritus associated with spinal opiate analgesia in man is thought to result either from release of histamine or from imbalance of sensory modulation secondary to spread of opiate to the medulla or fourth ventricle. There is another possibility: the sensory imbalance may be secondary to rostral spread of opiate effect by nervous transmission. Evidence is adduced in support of possible anatomical pathways, and in support of a medullary 'itching centre' in man.