Local administration of norepinephrine in the stump evokes dose-dependent pain in amputees

BACKGROUND: More than 50% of amputees report experiencing significant stump or phantom pain. Stump pain is often attributed to the formation of a neuroma at the amputation site. Experimental evidence shows that catecholamines and α-adrenoceptors play a role in the mechanisms of pain associated with neuromas. We investigated whether administration of physiological doses of norepinephrine (NE) in the distal stump in the region of a probable neuroma evoked pain and if local administration of phentolamine attenuated NE-evoked pain in patients with postamputation stump pain. METHODS: Twenty patients with postamputation stump pain participated in the study. In 15 patients, 0.2 mL of saline and NE (10, 10, and 10 molar concentrations) were administered sequentially in a single blinded fashion in the region of maximal tenderness and Tinel sign, a probable site of a neuroma. In 12 of these 15 patients, pain evoked by 0.2 mL of 10 M NE was examined before and after the injection of 0.2 mL phentolamine 10 M. Patients rated their pain using a computer-based visual analog scale. The area under the curve was calculated for pain evoked by each injection and the scores were normalized to the first saline injection. RESULTS: The perineuronal administration of NE had a dose-dependent increase in pain (P=0.005). In contrast, repeated saline injections did not result in increased evoked pain. There was a partial reversal of the pain evoked by 10 M NE after pretreatment with phentolamine (NE 10 M prephentolamine versus normal saline P=0.02, NE 10 M postphentolamine versus normal saline P=0.054). CONCLUSION: Our data suggest that α-adrenoceptor mechanisms contribute to stump pain, possibly associated with neuromas in amputees. Sympathectomy and adrenergic blockade should be explored in controlled clinical trials as therapeutic options in patients with postamputation pain.