Sensory and motor evoked potentials findings in patients with thoracic outlet syndrome.

Objective: Diagnostic utility of somatosensory and motor evoked potentials in two patients with neurogenic and vascular thoracic outlet syndrome (TOS) were investigated. Materials and methods: In two female patients with progressive weakness and sensory disturbance of the arms, mixed nerve somatosensory evoked potentials (SSEP), and motor evoked potentials (MEP) were tested before and after dynamic position of the affected arm. Results: The cortical and cervical (C7) ulnar SSEPs demonstrated no change in latency of major peaks at rest and after abduction of the shoulder. A slight diminishment of cortical amplitude was noted in the first patient after the dynamic position of the arm. The MEPs demonstrated significant drop in amplitude after dynamic position of the arm in both cases signifying neurovascular compression during elevation of the affected arm. No change in MEP latency was noted. The MEP amplitude completely returned to normal after repositioning the arm. Conclusions: Evoked potential studies are helpful in the diagnosis of neurogenic or vascular TOS. Reduced amplitude of MEP occurs after elevation of the arm above the head which improves after normal position of the arm.