Vestibular evoked myogenic potential seminar

Vemp

1. VEMP VESTIBULAR EVOKED MYOGENIC POTENTIAL A. Santhosh kumar N II UNIT

2. SCOPE INTRODUCTION ANATOMY OF VESTIBULAR SYSTEM TYPES OF VEMP REFLEX PATHWAYS MEDIATING VEMP CERVICAL VEMP TECHNIQUE STIMULUS PARAMETERS RECORDING PARAMETERS CLINICAL APPLICATIONS OCULAR VEMP PRACTICE GUIDELINES CONCLUSION

3. INTRODUCTION VEMP is a neurophysiological assesment technique used to determine the function of the otolith organs ( utricle and saccule ) of the inner ear. These  sensory organs in the inner ear  primarily respond to linear acceleration such as due to orientation to gravity, but the saccule and utricle are also sensitive to sound. This is the basis of the VEMP test. It complements the information provided by other forms of vestibular appartus testing ( Caloric testing,ENG /VNG, etc.)

4. VEMP Otolith organs have a slight sound sensitivity and this can be measured This sensitivity is thought to be a remnant from the otolith organs use as an organ of hearing in lower animals .

5. A myogenic response from muscles of the neck (or eyes), in response to high level acoustic stimulatio n. VEMP s are short latency,vestibular -dependent reflexes that are recorded from the sternocleidomastoid (SCM) muscles (cervical VEMPs) and the inferior obliqu e extraocular muscle(ocular VEMPs) . US FDA approved VEMP in Oct 2015. VEMP testing assesses the function of saccule /utricle.

6. ANATOMY OF VESTIBULAR SYSTEM

7. TYPES OF VEMP c VEMP - Assess saccu lar vestibular signals via the inferior vestibular nerve (vestibulospinal tract ) o VEMP - Asses vestibular signals from the utricle via the superior vestibular nerve

8. REFLEX PATHWAYS MEDIATING VEMP C VEMP Saccule Inferior vestibular nerve Vestibular nuclei Vestibulospinal pathway Spinal accessory nerve The cervical VEMP ( cVEMP ) is an inhibitory electromyographic (EMG) signal measured over the contracted sternocleidomastoid (SCM) muscle ipsilateral to the ear being stimulated with sound.

9. c VEMP The vestibulocollic reflex can be used to assess saccular function via a cervical vestibular evoked myogenic potential The stimulus is a loud sound that stimulates the saccule. Through the inferior vestibular nerve, the response travels to the vestibular nuclei in the brainstem, from where it projects via the vestibulospinal tract to the motor neurons of the sternocleidomastoid muscle. There, the response modulates the tonically contracted muscle by means of an inhibitory pulse.

10. cVEMP The cVEMP is an ipsilateral reflex, faster than the startle reflex Unlike the startle reflex, it is not fatigable. The ipsilateral inhibitory aspect of the cVEMP may imply that the reflex redirects the head in the direction of the loud noise. Sensorineural hearing is not necessary to obtain a VEMP.

11. TECHNIQUE The equipment necessary to record cVEMPs is standard for evoked potential studies. VEMPs are recorded using an evoked response computer, a sound generator, and surface electrodes Surface electrodes typically are placed as follows: 1. Active electrode on the belly of the ipsilateral sternocleidomastoid muscle 2. The reference electrode on the sternum 3. Common ground electrode on the forehead.

12. Ground electrode ACTIVE ELECTRODE REFERENCE ELECTROD E

13. The patient is either in sitting or in lying down position with the sternocleidomastoid muscle in contraction. The responses are better obtained with patient in lying down position.

14. STIMULUS PARAMETERS Loud stimuli are necessary to elicit the response. Recording a cVEMP requires approximately 30 seconds per trace 250 stimuli are sufficient to record a response. Initially,100-ms clicks at 100 dB HL were used, but more recently, short tone bursts of 500 Hz (100 dB HL, rise/fall-time 1 msec , plateau 2 msec ) are used

15. The cVEMP has a typical biphasic waveform and a latency in the order of 10 to 30 msec .

16. RECORDING PARAMETERS Latency Amplitude -The amplitude of the cVEMPis proportional to the contraction state of the sternocleidomastoid muscle. Threshold - (least intense sound stimulus to still yield a reliable response)

17. The waveform shows the positive – negative cVEMP (p13-n23) on the side to which the sound stimulation is applied. Measurements include the latency, the amplitude, and the threshold. The responses occur only on the side of the sound stimulation.

18. NORMAL LATENCIES P 13- 13- 20 ms N23 - 20-30 ms NORMAL THRESHOLD VALUES • 80 dB nHL +/- 10 dB • <15 dB asymmetry between ears VEMP Ratio or IADR = (Amp[left]- Amp[right]) ----------------------------- X 100 (Amp[left]+Amp[right]) An amplitude asymmetry > 30-47% is considered clinically significant.

19. CLINICAL APPLICATIONS Pathologically lowered thresholds: ––superior canal dehiscence (SCD) ––benign proxysmal positional vertigo (BPPV) ––vestibular hypersensitivity disorders Absent or decreased potentials: –– Ménière’s disease ––vestibular schwannoma (acoustic neuroma) ––vestibular neuritis ( neuronitis , neuropathy) ––multiple sclerosis –– otosclerosis

20. • Increased latencies: ––vestibular schwannoma (acoustic neuroma) ––benign proxysmal positional vertigo (BPPV) ––multiple sclerosis ––Guillain–Barré syndrome (GBS) The general rule of thumb with hearing and VEMPs is that conductive hearing loss obliterates VEMPs, and sensorineural hearing loss does little or nothing to VEMPs.

21. OCULAR VEMP Measures vestibular function from the utricle-  superior vestibular n- contralateral MLF  Oculomotor nucleus Stimulus – air or bone conducted sound Biphasic waveform - n10 ,p16

22. oVEMP  Subjects fix their gaze on a line on the ceiling that was located 30-degrees up Active electrode placed on the cheek approximately 5 mm below the eyelid and centered beneath the pupil Inverting electrode placed centered 2 cm below the active electrode Ground electrode placed on the manubrium sterni /forehead.

23. o VEMP utricle superior vestibular nerve ipsilateral vestibular nucleus contralateral MLF Inferior oblique subnucleus The oVEMP is an excitatory EMG response generated primarily by the inferior oblique muscle contralateral to the stimulated ear

24. Vestibular evoked myogenic potentials (VEMPs) are a useful and increasingly popular component of the neuro-otology test battery. cVEMP may have important diagnostic and management implications, even though it is not diagnostic in isolation. VEMPs have a clear role in the diagnosis of superior semicircular canal dehiscence.

25. Superior canal dehiscence syndrome (SCDS) It is characterized by a combination of vestibular and auditory signs and symptoms Vestibular manifestations include vertigo and oscillopsia in response to sound and/or pressure  Auditory complaints include autophony, bone-conductive hyperacusis and pulsatile tinnitus

26. SCDS The cVEMP has been found to show abnormally low thresholds and enlarged peak-to-peak amplitudes in SCDS The rationale is that the dehiscent semicircular canal lowers the impedance of the vestibular system Tullio phenomenon  - precipitation of vertigo and nystagmus by a loud noise ( Inceased sensitivity of otolith organs) Thus, cVEMP signals are enhanced in patients with SCDS.

27. oVEMP in SCDS In the setting of SCDS, oVEMPs also depict lower thresholds and increased amplitudes even to a greater extent to that observed in cVEMP responses In surgically-confirmed SCDS, cVEMP amplitudes in response to 500 Hz tone bursts (TB) showed approximately a 2-fold mean increase compared with controls, whereas oVEMP amplitudes in response to the same stimulus showed a 10-fold increase   oVEMP amplitudes are more sensitive and specific than cVEMP thresholds for the diagnosis of SCDS.

28. Cervical VEMP Ocular VEMP consequence of saccular activation Predominantly utricular activation Intact Inferior vestibular nerve Intact Superior vestibular nerve Inhibitory electromyographic (EMG) signal  Excitatory EMG respons Measured over sternocleidomastoid (Ipsilateral) Measured over  inferior oblique muscle (contralateral) Biphasic waveform - p13 ,n23 Biphasic waveform - n10 ,p16

29. Specific vestibular sensory system (saccule) is assessed Retained in patients with profound SNHL Used in infants (latencies are shorter) Highly sensitive in the early diagnosis of retrocochlearlesions Robust, reproducible screening test of otolith function Minimal test time Easy to obtain & interpret Non-invasive, bedside test Does not cause discomfort VEMP advantages

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