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Diagnostic importance of somatosensory evoked potentials in the diagnosis of thoracic outlet syndrome.

Somatosensory evoked potentials (SEPs) after stimulation of median and ulnar nerves were analyzed retrospectively in a group of 14 patients presenting with rudimentary cervical ribs or ill-healed clavicular fractures, where clinically the possibility of thoracic outlet syndrome was raised. In 5 patients who presented with pain in the arm and hypoesthesia along the ulnar border of the forearm without weakness and wasting in the muscles supplied by the lower trunk of the brachial plexus, the SEPs after both median and ulnar nerve stimulation were normal. In the second group of 9 patients there was weakness and wasting of the lower trunk-supplied muscles. All these patients were treated surgically by excision of abnormal tissues; all of them improved subjectively, and most of them improved strength in the previously affected muscles. SEPs in this group recorded preoperatively showed normal findings after median nerve stimulation, while the potentials after stimulation of ulnar nerve were always abnormal from the affected arm, being delayed, attenuated or even absent at Erb's point, cervical spinal cord and contralateral scalp. The results of this study, which were based on 314 investigations performed in patients with different lesions of the brachial plexus, suggest that abnormal ulnar nerve SEPs in the presence of normal median nerve SEPs are supportive means in the diagnosis of thoracic outlet syndrome, where nervous structures have been endangered. This is in accordance with the most recent reports in the literature.