Triceps Acoustically Evoked Myogenic Potentials in Patients with Spinal Cord Lesions

Objective (Background): Vestibular evoked myogenic potentials (VEMPs) are used to evaluate function of the vestibular system. Sound evoked triceps myogenic potentials (SETMPs) have not been studied extensively and differ anatomically from sternocleidomastoid (SCM) VEMPs because the efferent pathway for SETMPs traverses the spinal cord. The aim of this study was to examine whether SETMPs in people with spinal cord lesions have reduced amplitude or longer latency compared to responses in a group of asymptomatic controls without spinal cord lesions. Methods: We tested a group of 15 subjects with lesions in the cervical spinal cord and a group of 11 normal (asymptomatic) subjects. All subjects had normal hearing and normal vestibular function as determined by pure tone audiometry and normal SCM VEMPs respectively. All subjects were tested for presence of responses on SCM and SETMPs using methodologies previously established. Results: Nine of the subjects with spinal cord lesions had bilaterally absent SETMP response and the other five only had a response on one side. The unilateral responses were lower in amplitude than the responses in the control subjects. The control subjects all exhibited a SETMP response. Conclusions: We found the SETMP response absent bilaterally in 67% and unilaterally in 33% of subjects with cervical cord lesions. This suggests that SETMPs are sensitive to cervical cord injury.