Cutaneous hypersensitivity following peripheral tissue damage in newborn infants and its reversal with topical anaesthesia.

The flexion reflex threshold has been used as a measure of sensation in a group of premature infants born at 27-32 weeks postmenstrual age. The threshold in an area of local tissue damage created by routine heel lances was half the threshold on the intact heel on the other side. This indicated a hypersensitivity to tissue damage analogous to tenderness or hyperalgesia reported in adults. In a double-blind study, treatment of the damaged area with the topical anaesthetic cream, EMLA, was found to reverse this hypersensitivity or in other words increase the flexion reflex threshold. Treatment with placebo had no effect. The results show that the newborn infant central nervous system is capable of mounting a chronic pain response to local injury which can be reduced by local anaesthetic.