Quantitative sensory testing before and after regional guanethidine block in patients with neuralgia in the hand.

Using reference values from healthy volunteers, thermal and vibration-induced pain thresholds and the sensibility for warm and cold were studied in 18 patients with neuralgia in one hand following a traumatic injury or surgery. All patients had spontaneous pain and allodynia to vibration. They were treated with intravenous regional guanethidine block (RGB). Quantitative sensory testing was performed on both hands before and 1-3 days after treatment. Eleven patients benefitted considerably from the block, with pain relief for 2 weeks or more. Ten of these 11 patients had mild nerve injuries caused by compressive trauma to the nerve. Before RGB they showed a moderate loss in temperature discrimination capacity; their heat pain thresholds were reduced and they exhibited allodynia to cold and vibration on the injured side. After RGB, the pain thresholds were normalised both to thermal and vibratory stimuli. These patients were classified as having sympathetically maintained pain (SMP). Seven patients reported no or only minor pain-relieving effect of RGB lasting 1-5 days. Severe nerve injuries were most frequent in this group of patients. On the injured side, before RGB, their ability to discriminate between warm and cold was markedly impaired, thermal pain thresholds were normal, and they showed allodynia to vibration. After RGB, there was no change in thermal pain thresholds and the allodynia to vibration persisted. These patients were classified as having sympathetically independent pain (SIP). The results indicate that quantitative thermal sensory tests, together with clinical evaluation of the nerve trauma, can help to predict which patients will have long-lasting pain alleviation after RGB treatment.