EVOKED-RESPONSES IN THE DIAGNOSIS OF THORACIC OUTLET SYNDROME

Abstract

The lack of an objective method for diagnosing thoracic outlet syndrome and monitoring the results of treatment has prevented a clear understanding of its natural history and the indications for surgery. Although vascular compression can be detected, the majority of patients have symptoms that are primarily neurogenic. Neither electromyograms nor studies of nerve conduction velocity was consistently helpful in their evaluation. Evoked responses were studied in 22 patients. This technique apparently allows selection of patients with significant neural compression for operative treatment. A bipolar stimulating electrode is placed on the median and ulnar nerves at the wrist. A bipolar recording is performed from active electrodes placed at Erb''s point, over the spines of C[cervical vertebra]6 and C2 and over the contralateral pariental scalp, all referenced to a midfrontal electrode. A minicomputer temporally summates the low-amplitude potentials elicited by repetitive electrical stimulation to increase the signal to noise ratio and distinguish the potentials of interest from the background bioelectric activity. Normative values were determined, allowing detection of changes in conduction of the electrical activity that occur between the sites of stimulation and the sites of recording. Of 19 new patients, 13 had abnormal evoked responses. Nine of these underwent surgical treatment; 8 obtained good or excellent results. Abnormalities in evoked responses disappeared after operation in 7 of the 8 in whom it was measured. Four patients with abnormal responses, but no surgery, are being evaluated. Two of 3 long-term patients with recurrent symptoms had abnormal evoked responses that changed after treatment. Longer follow-up is needed to determine if this method is helpful in selecting patients for operative treatment or in monitoring its results.