Session 7- VEMP Flashcards
how do we measure the function of the utricle and the saccule organs?
using VEMP
how many types of VEMP are there?
1=cVEMP is recorded from the neck (sternocleidomastoid muscle ) and measures the function of the saccule and inferior vestibular nerve
2=oVEMP is recorded from the eye and reflects primarily utricular function
what does cVEMP stand for?
Cervical Vestibular Evoked Myogenic Potential
how do we elicit (evoke) cVEMP?
by using either:
-acoustic
-vibratory
-galvanic
what is the most common method of recording cVEMP?
-using an acoustic stimulus, either a 2-1-2 or 2-2-2 tone burst at a loud intensity usually at around 95dBnHL
- the response is then recorded by using surface electrodes at fore-cites at the head and neck
what is the most common electrode montage for cVEMP?
is to record from the clavicular joint, forehead and each sternocleidomastoid muscle
what is it important for the patient to do to record a cVEMP?
to maintain a contracted sternocleidomastoid muscle.
- the patient is instructed to either turn their head left or right depending on which side is stimulated
how can a patient monitor their muscle contraction?
-visually by using a patient ENG monitor or audibly by using a ENG monitor tone
How is the cVEMP represented?
by 2 dystinct peaks. P1 occurs at approximately 13 milli seconds and N1 at approximately 23 milli seconds
p13n23 comples, anything after n23, is cochlear in origin so ignore
what is the purpose of the cVEMP?
its a clinical method of assessing the integrity pf the saccule, inferior vestibular nerve and VCR pathway in humans
- it forms an ipsilateral waveform response generated by activation of vestibular afferents.
what does the latency of the cVEMP waveforms depend on?
the design and stimulus chosen to elicit the cVEMP
how do we ensure even muscle contraction?
using ENG scaling (Amplitude normalisation)
how is the amplitude, latency and threshold be analysed/ measured?
using cVEMP
What ratio is used in cVEMP testing to detect vestibular dysfunction?
the amplitude ratio between the right and left ears
a difference greater than 36% is indicative of vestibular dysfunction
what can cVEMP be used for?
can detect Superior semicircular canal Dehiscence, Saccular Dysfunction as well as disorders of the Inferior Vestibular Nerve
What is VNG used for?
to asess vestibular and occular motor function VOR
what is vHIT used for?
to assess function of all 6 semi-circular canals
what does oVEMP stand for?
Ocular Vestibular Evoked Myogenic Potential
which muscle is the oVEMP measured from?
the evoked potential is measured from the Inferior Oblique muscle
Which vestibular structures and nerve does the oVEMP test primarily depend on?
its largely dependent on the utricle and the superior vestibular nerve
what kind of stimulus evoke the oVEMP?
-Acoustic (most common)
-Vibratory
-Galvanic
what is the most common method of recording oVEMP?
-using an acoustic stimulus using a 2-2-2 tone burst at a loud intensity usually at around 95dBnHL
what is the most common electrode montage for oVEMP?
- the response is then recorded by using surface electrodes at fore-cites at the Underneath each eye, Chin, Forehead (Ground).
the oVEMP is largest when recorded contralaterally which is why the right reference electrode is placed underneath the left eye.
what is the patient positioning and instructions for oVEMP?
- patient should be seated or reclined
- maintain a upwards gaze of 35 degrees for the duration of the recording
How is oVEMP represented?
by 2 distinct peaks. N1 occurs at approximately 10 milli seconds and P1 at approximately 15 milli seconds
- you do the tone presentations for the 100-150 times, we do a weighted add, where it adds these results together and gives an average of them
what information can be interpreted with the oVEMP?
-amplitude
-latency
-threshold
what is the most robust ratio to analyse with oVEMP?
Amplitude ratio between right and left ears.
A difference of >33% is a sign of dysfunction
What is the benefit of combining oVEMP with other vestibular tests like vHIT and VNG
it helps assist diagnose:
- SSCD (superior SemiCircular Dehiscence)
- Meniere’s Disease
-disorders of the superior superior vestibular nerve
what does VEMP stand for?
Vestibular - comes from the vestibular system (sound evoked stimulus via air conduction- patients don’t have to hear the sound
Evoked- in response to a stimulus
Myogenic- its a muscle response that we are recording
Potential- we place electrodes on the skin to record this muscle changes
what part of the structure for VEMPs test?
the otolith organs
what otolith organ is being tested with each VEMP test?
cVEMP= saccule
oVEMP= utricle
what happens with a cVEMP?
1- play a aloud air conduction stimulus to the ear
2- this stimulates the primary afferents of the saccular macular
3- info is relayed along the inferior vestibular nerve up to the vestibular nuclei
4- the info reflexed down the vestibular spinal tract via the vestibular colic reflex
5- its contracts the SCM in the neck
6- we record a change in the tonicity of the muscle
is the cVEMP and ipsi or contralateral test?
its a ipsilateral, you play the sound in the left ear, the left muscle contracts
for a cVEMP test, does the patient need to hear the stimulus?
no, the sound creates a travelling wave of pressure that stimulates the otolith organs
how does the oVEMP work?
1- stimulus comes from the utricle, travels along the superior vestibular nerve to the vestibular nuclei
2- neural signals crosses over the mid line and uses the VOR (vestibular ocular reflex)
3- as it comes down to the eye muscles, we record the muscle tonicity in the extraocular muscle
is the oVEMP and ipsi or contralateral test?
this is a cross response, stimulus the left ear, we record the muscle tonicity in the right eye muscle BUT its still testing the left ear
what are the differences between the cervical VEMP and the ocular VEMP?
- Cervical VEMP:
- believed to come from the Saccule
- travels along the inferior vestibular nerve
-the reflex is measures at the Sternocleidomastoid muscle - Its an inhibitory response
- Its ipsilateral
*Ocular VEMP:
- believed to come the Utricle (depending the stimulus used)
- travels along the Superior vestibular nerve
- Reflex is measured at the Extraocular muscle
- Its an Excitatory response
-Its Contralateral
=oVEMPS are really easy to record but the oVEMP is really hard to record.
what are cVEMP contraindications?
-cervical spine problems
-conductive hearing loss- because the sound isn’t conducted throughout the ear
-hyperacusis and tinnitus as it can aggravate these
what are the steps for measurements of cVEMPs?
1- use nuprep to remove any dead skin cells
2- place an electrode on the forehead
3- place the active electrode on the midpoint of the SCM on the neck
4- place the reference electrode on the sternoclavicular joint (bit above the collar bone)
5- tell patient to active the sternocleidomastoid muscle (tonicity of this muscle directly affects how big our recordings are.
6- present a high level acoustic stimulus approximately 95 dBnHL to ipsilateral ear
7- use a very short tone burst, because ts so short in duration, it doesn’t sound uncomfortable
what do we need to ensure the patient does so that we can compare cVEMP recordings on each side?
equally tense their neck on both sides
how does the patient activate the neck muscles (sternocleidomastoid) ?
tell the patient to lie down flat and lift their head
or you can push the patients head and they use their forehead to push your hand away
-or MOST COMMONLY turn your head 45 degrees to the side you’re not testing and dip your ear towards the floor
*hold the position for about 45 seconds
for cVEMPS, which frequency has the largest reponse?
500Hz
how do we record cVEMPs?
100-150 sweeps (30-40 seconds). We do this once, let the patient rest and do it again.
- then we do a weighted add, where it adds these results together and gives an average of them
why do we record cVEMPs unilateral?
because there’s a cross response that we don’t want to be interpreting
so, we ensure equal EMG activity is maintained for both the left and right sides to allow accurate comparisons
what are some common pitfalls for cVEMPs?
- conductive hearing loss: an air-bone gap as small as dB can effect recordings as the stimulus is too quiet so we don’t get the travelling wave for them.
- we don’t get the patient to tense their neck enough, the more tense the neck, the better the recording.
- stimulus too quiet
- insufficient muscle tonicity
- electrode placement
what kind of stimuli can be used to elicit a cVEMP or oVEMP response and why the different stimuli?
-Both oVEMPs and cVEMPs can be elicited in response to air conduction, bone conduction and electrical stimuli.
*Reasons for different stimuli:
- clinical differentiation between retrolabryinthine and labyrinthine lesions.
- AC cVEMP responses were lose in subjects with air-bone gaps as small as 8.75
what is interaural amplitude comparison
just work out whether the waveform on the right side and the waveform on the left side are the same size.
Right vs Left
How do you interpret cVEMP and oVEMP tracings?
1-is there a presence of a waveform. flat line is no VEMP response
2- if you get the presence of a waveform on both sides, compare which is larger vs smaller
what does a VERY late latency suggest?
some kind of central pathology but we don’t really use latency to interpret VEMPs
how do we know if the level of asymmetry is abnormal?
we calculate the Asymmertry Ratio (AR) or Saccular Paresis
- most commonly 40% + difference between R & L VEMP response is abnormal
what is the clinical use of VEMPS
NOT EVERYONE HAS ACCESS TO THIS EQUIPMENT but we use it for:
- patients with complaint of sound- evoked vestibular symptoms
- these patience often have SCCD (Dehiscence- the thinning or disappearance of the temporal bone(bony labyrinth) , makes them dizzy as it creates an extra window on top of the oval window )
- assessment of the otoliths and vestibular nerve to identify vestibular pathologies (e.g. acoustic neuroma), such as Meniere’s disease or vestibular neuritis
What kind of VEMPs would someone with Superior canal dehiscence syndrome have?
- they get VEMPs at very low levels that we would expect VEMPs to be obliterated at.
- Dehiscence of the bony labyrinth and development f a third window in the superior semicircular canal.
- VEMP abnormalities can be used in the diagnosis of SCDS
- Pathological hypersensitivity to sounds will result in high amplitude Reponses to low threshold stimuli (70dBnHL or below) in repose to both AC and BCV stimulation.
would a normal person have VEMPS around 80?
no 80, 70 is too low. 95 is good
what do peak latency delays tell us
Peak latency delays can be used to signify retrolabyrinthine or central
pathologies
What is the asymmetry ratio (AR) in VEMPs, and what is its clinical significance?
- The asymmetry ratio (AR) measures the difference in VEMP amplitudes between the right and left sides.
- Values greater than 40% are typically considered abnormal.
-Indicates possible unilateral vestibular dysfunction, such as:
Saccular paresis (saccular dysfunction).
Inferior vestibular nerve abnormalities.
what is the calculation for asymmetry?
LA-SA/ R+L
LA- larger of the left or right amplitude
SA- smaller of the left or right amplitude
R- right amplitude
L- left amplitude
How to tell if there is an abnormality in oVEMP results
Check the asymmetry ratio between left and right ear
If there is a difference of more than 33% there is dysfunction
