Vestibular Evoked Myogenic Potential (VEMP) Testing -- Cervical (SCM). Normal Values
Timothy C. Hain, MD
Page last modified:
September 12, 2019
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See also: oVEMP norms. We have many other VEMP pages, which are linked to by the main two pages (vemp.html and ovemp.html).
We have done a large number of cVEMPs at our clinic setting in Chicago, as we started doing VEMPs in 2010. We use tone-burst VEMPs, which produce modestly larger responses than clicks. We tried bilateral binaural recording and stimulation, but we switched back to monaural stimuli because of some bad diagnostic experiences where it appeared that there was a VEMP with binaural stimulation, but there was clearly no VEMP with monaural stimulation. We have tried other methods than head-lift, and decided that head-lift is the best. We have tried rectification, and decided this was too noisy. So these are unrectified, monaural, head-lift VEMPs.
The graph above shows the distribution of cVEMP amplitudes in "all comers", which means everyone who had a test done and results in the database (usually these are dizzy people), excluding patients with a diagnosis of SCD. The most prevalent diagnosis is migraine, where VEMPS are expected to be normal. However, this collection includes some patients with vestibular neuritis, some very old people, etc -- in other words, some of the low potentials may be due to illness. Still, this shows that about a third of dizzy patients have cVEMP amplitudes between 200-300. There are just a few people with very high amplitudes -- and only about 1% of our patients had cVEMPs over 500. We generally do NOT make diagnoses using cVEMP amplitudes, although this data would suggest it should be possible as the distribution is actually fairly tight. Instead we rely on asymmetry and especially thresholds.
Criteria for abnormality.
VEMPS to be abnormal when they are very asymmetrical (one is 2 times or more
as large as the other -- an RVR of 33% or greater), low in amplitude (less than 70 for a young population -- see below), or absent (no reproducible wave, or P1 latency outside of our norms). Regarding thresholds, we strongly consider SCD when the thresholds are <=65.
We do not pay much attention at all to latencies -- our thought is that they have no diagnostic utility. Sometimes we use latencies to decide that whatever we are measuring is not a VEMP at all.
Age and Vemp Amplitude
|Figure: VEMP amplitude to clicks, as a function of age, from Su et al (2004).
||VEMP amplitude to tone bursts, as a function of age from Rosengren et al, 2011. Here amplitudes are normalized to background EMG. This is uncommon in clinical settings.
Concerning effects of age, 3 studies have been done -- using 3 different techniques. For clicks, compared to young persons, decreased amplitudes (roughly a factor of two) are
seen on persons 70 and older (Su et al, 2004). Similarly, also using clicks but not using commercial equipment, Ochi reported amplitudes of approximately 250 for 20 year olds vs. 90 for 80 year olds.
Basta et al reported similar results for 500 hz tone bursts (2007) but with lower overall amplitudes using a Viking system. These systems seem to produce lower amplitude results, perhaps due to differences in calibration. It has been our general experience that the device that we use (Bio-Logic NavPro) produces larger potentials than most competing devices.
Rosengren et al (2011) reported a somewhat similar drop in amplitude with age. Note here that amplitudes are normalized with respect to background EMG activity, and are not equivalent to the amplitudes of Su which are not normalized. We prefer the non-normalized VEMPs.
||Su et al
||Su et al
||18.24 +- 1.33
||Su et al
||Su et al.
||0.16 +- .12
At the present writing (2011), it appears to us that in normal persons, and using the Bio-logic Nav-Pro, average VEMP amplitude decline from approximately 150 at the age of 20 to approximately 75 at the age of 70.
As both cVEMPs and oVEMPs decline with age, and because the otolith organs have "moving parts", it would seem likely to us that the otoliths simply wear out -- otoconia are shed, and response amplitude goes down.
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