Vestibular Evoked Myogenic Potentials (VEMP)


Otolithic Evoked Potential (OEP) or Myogenic Vestibular Evoked Potential (VEMP) are sacculo-collique reflex recorded in response to an acoustic stimulation. They study the sacculo-spinal way: the sacculo, inferior vestibular nerve from the sterno-cleido-mastoid (SCM) ipsilateral, via cervico spinal cord. The OEP or VEMP are recently used in the battery of cochleovestibular investigation tests and reinforce the aid diagnostic in addition to other tests such as audiogram and Auditory Brainstem Response (ABR).

 

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Method: Sounds stimulations of high intensity (90-100 dB) activate primary vestibular neurons innervating the saccule and secondary vestibular neurons of nucei inferior and side vestibular. In practice short sounds clicks (100 microseconds) or short tone bursts from 90 to 100 dB are unilaterally issued by using an acoustic stimulation at 1 KHz or 500 Hz frequency. OEP are collected at the two SCM muscles through skin electrodes placed at the 1/3 superior part of these two muscles. During recording, patients are placed lying supine with a head position elevated to increase the SCM muscle contraction. Sometimes it's useful to turn the head on the opposite side of the stimulation to increase the muscle contraction. Indeed it's a necessary condition because the evoked potentials amplitude is correlated with the SCM muscle contraction amplitude. VEMP are then amplified, filtered and averaged on 500 stimulations. Saccule being innervated by inferior vestibular nerve, such as posterior CCS, results is complementary to choose obtained by using caloric tests, which in testing the external canal, evaluate the function of the higher vestibular nerve. This test assesses the functioning of saccule receptors and sacculo-spinal channels.

 

Echodia devices allowing VEMP measurements: ELIOS and ELITE.