Aim of the study: Click-evoked myogenic potentials (CEMPs) originate in the sternocleidomastoid (SCM) muscle through a reflex loop involving the sacculus and the vestibular nerve. In this study we suggest that they can be picked up from the mastoid reference used for auditory evoked potential (AEP) recording by using standard filters for brainstem AEPs (BAEPs). They consist of a P13-N20 complex.
Methods: Fifty normal subjects were investigated. Recordings were performed with the same setting as that used for conventional BAEPs but without artifact rejection and using a wide time window (100 ms). Unilateral auditory stimulations were used. All acquisitions were performed in both sitting and supine positions. In nine subjects CEMPs and BAEPs were simultaneously recorded at both earlobe and both SCM muscles.
Results: In all subjects, a CEMP P13-N20 component could be evidenced in sitting, but not in supine position at both the ipsilateral earlobe and the ipsilateral SCM muscle. Its latency was 0.7 ms lower at the earlobe. It obeyed the same relationship to stimulus intensity at both earlobe and SCM muscle.
Conclusion: These results demonstrate the possibility to get simultaneous information on the brainstem auditory pathways and on a reflex probably mediated through the sacculus and the vestibular nerve. Further studies on patients with selective vestibular nerve impairment should be conducted to confirm the clinical utility of this approach.