Objective: To determine if an evoked myogenic potential could be obtained from the gastrocnemius of the leg with similar recording and stimulus parameters to those routinely used to obtain vestibular-evoked myogenic potentials from the sternocleidomastoid (SCM) of the neck.
Study design: Prospective study in which we recorded evoked myogenic potentials from the gastrocnemius and compared it with the response obtained at the SCM.
Setting: University-affiliated hearing clinic.
Patients: Twelve healthy adult volunteers and 1 patient with bilateral vestibular loss were studied. Ages of the healthy subjects ranged between 18 and 54 years.
Main outcome measure(s): Myogenic potentials evoked by tone-burst stimuli (95 dB hearing level, 500 Hz) were recorded with surface electrodes over each gastrocnemius and SCM muscle and averaged. Latencies and amplitudes of the responses were measured.
Results: Responses were obtained in the gastrocnemius, both ipsilateral and contralateral to the acoustic stimulus. The response consisted of 2 biphasic waves (P1-N1 and P2-N2), although not all subjects exhibited both components. The most reliable wave was P2-N2, which was measured ipsilaterally in 81% of the subjects and contralaterally in 68%. Responses were smaller and later than those in the SCM.
Conclusion: An acoustically evoked myogenic potential can be recorded from the leg using the same stimulus that is routinely used to obtain a vestibular-evoked myogenic potential response from the SCM. The presence of this response in the leg ipsilateral and contralateral to the stimulated ear suggests that the response travels via crossed and uncrossed pathways in the spinal cord.