BENEFICIAL-EFFECTS OF KETAMINE IN A CHRONIC PAIN STATE WITH ALLODYNIA, POSSIBLY DUE TO CENTRAL SENSITIZATION

Allodynia is a well-known component of neuropathic pain resulting from injury to the nervous system. Clinical pain states with allodynia in connection with longstanding superficial wounds have, however, not bee n reported in the litterature. In this case a chronic pain state devel oped in a previously healthy 17-year-old girl in and around a persiste ntly suppurating appendectomy wound. There was no spontaneous pain but pronounced allodynia in the wound and in the surrounding skin. Quanti tative thermal tests showed abnormal thresholds for several sensory mo dalities confirming abnormal processing of sensory input from the invo lved area. The pattern of sensory abnormalities evaluated with thermal testing changed transiently and the allodynia diminished during a phe ntolamine block. Since the pain responded poorly to opioids and ketami ne has been reported to reduce allodynia, it was administered in a sub -dissociative bolus dose during wound dressing. The wound was essentia lly unchanged after treatment for 3 months but the allodynia and senso ry aberrations had decreased significantly. We interpret these results as a de-sensitizing effect in the long term of repeated NMDA-receptor blockade by ketamine in a chronic pain state, with indications of cen tral sensitization, partially maintained by sympathetic activity.