Dynamic approach in the diagnosis of thoracic outlet syndrome using somatosensory evoked responses

The clinical diagnosis of thoracic outlet syndrome (TOS) is controversial. Objective documentation of this disorder is often unobtainable, even with electrodiagnostic techniques. This preliminary report describes an objective diagnostic method of evaluating TOS using somatosensory evoked potential testing (SEP) and dynamic arm positioning. Evoked potentials were recorded over the brachial plexus (N9) and C7 cervical vertebra (N13) after distal stimulation of the median and/or ulnar nerves. This was performed with the arm both at the side (anatomic position), and then positioned in abduction and external rotation. Absolute and interpeak latencies were measured in both positions. Of 14 patients clinically suspected of having TOS, six showed normal N13 evoked responses in the anatomic position despite a disappearance of this potential when tested with the symptomatic arm in the dynamic position of abduction and external rotation. Fourteen control subjects had normal responses with the arm tested in both positions. The SEP coupled with the dynamic stress of the nerves coursing through the thoracic outlet may be helpful as a new objective aid in the diagnosis of TOS.