THE INTERPRETATION OF PAIN RELIEF AND SENSORY CHANGES FOLLOWING SYMPATHETIC BLOCKADE

A comparative study of the effects of sympathetic blockade by stellate ganglion block (SGB) and intravenous phentolamine infusion (Phl) was carried out in 24 patients with presumed sympathetically maintained pa in of an upper extremity. A total of 15 SGBs and 16 PhIs were performe d with seven patients undergoing both procedures. All patients develop ed a Horner's syndrome with SGB and nasal stuffiness and cardiovascula r changes with PhI. Similar pain relief was obtained with SGB and Phl in six of the seven who underwent both procedures. Pre-procedure patie nt characteristics including age, sex, duration of pain, historical an d physical examination features suggestive of the reflex sympathetic d ystrophy syndrome, and sensory disturbances such as allodynia and hype rpathia did not predict pain relief from either procedure. Changes in skin temperature following the sympatholytic procedure did not correla te with pain relief For Phl, pain relief correlated with the magnitude of decrease in systolic blood pressure. After SGB, changes in quantit ative thermal sensory testing (QST) suggestive of a partial deficit in thermal sensation correlated with pain relief In 20 normal controls, water bath immersion to cool the hand passively by 7 degrees C and war m the hand passively by 4 degrees C had small and selective effects on thermal QST thresholds, but did not produce a general impairment in t hermal sensation. In conclusion, the diagnosis of sympathetically main tained pain based on the history and physical examination alone cannot be made with confidence and therefore a sympatholytic procedure is ne cessary. When SGB produces pain relief but Phl does not, systemic abso rption of local anaesthetic and/or sensory blockade by spread to somat ic nerves may be the reason. Thus, Phl appears so be a less sensitive but more specific test than SGB. These two procedures provide compleme ntary information and both may be needed to establish the diagnosis of sympathetically maintained pain.