Thoracic outlet syndrome. Electrophysiologic reappraisal.

Eighteen patients with thoracic outlet syndrome (TOS) were examined with somatosensory evoked potentials (SEPs). All the patients had normal median N9 (brachial plexus) amplitudes, whereas 12 had low-amplitude ulnar N9 potentials. The conduction in the ulnar nerve from N9 to N13 (brachial plexus to cord) was prolonged in seven of 18 patients. The combination of the ulnar N9 amplitude, the ulnar N9 to N13 conduction, and routine ulnar F-wave determination yielded positive quantitative diagnostic information in 17 of 18 cases. The SEPs appear to be a reliable, sensitive, quantitative, and non-invasive diagnostic tool in examining patients with TOS.