DIAGNOSIS OF THORACIC OUTLET SYNDROME USING ELECTROPHYSIOLOGICALLY GUIDED ANTERIOR SCALENE BLOCKS

There is no ''gold standard'' for diagnosing thoracic outlet compressi on syndrome (TOS), however, anesthetic blocks of the anterior scalene muscle (ASM) have been used as a means of predicting which patients ma y benefit from surgical decompression. The standard technique of using surface landmarks often results in inadvertent somatic block and symp athetic block because there is no reliable verification of needle tip localization. The present study was undertaken to determine if needle tip localization can be improved by using electrophysiological guidanc e. ASM blocks were performed for patients with a diagnosis of possible TOS. An insulated hypodermic needle was inserted into the ASM which w as identified during electromyogram (EMG) activation maneuvers. Stimul ation was performed to make sure that the needle tip was not in the br achial plexus. Local anesthetic was instilled and the intensity of pai n induced by TOS stress maneuvers was compared to pain ratings obtaine d after control injections. The ASM could be identified electromyograp hically in all 122 cases. There were no instances of inadvertent somat ic block nor sympathetic block. Of 38 patients who underwent surgical decompression of the thoracic outlet, 30 of 32 (94%) with a positive b lock had a good outcome compared with 3 of 6 (50%) who underwent surge ry in spite of a negative block. Electrophysiological guidance facilit ates accurate needle tip placement in the performance of ASM blocks; t he results of these blocks appear to correlate with surgical outcomes.