Irritative Lesions

[Britney Ears]

Does anyone have any thoughts on hyper-responses on caloric exam?
I recently saw a patient who had the following results with air calorics;

RW 12
LW 64
RC 22
LC 40 CP 51% DP 25%

Could anyone offer any insights/opinions into the following thoughts;
1. The Chartr VNG software flagged this result up as a technical error. However, given the large CP combined with DP, this result would seem physiologically valid. The software does not seem to take into account large responses in its calculation.
2. Any thought on what denotes a hyperfunction with air caloric? There do not seem to be any accepted norms, perhaps because different centres use different temperatures and flow rates and air caloric is less commonly used. It would seem reasonable that a hyperresponse for air would be lower than for water as it is generally considered a weaker stimulus. The patient had a strong subjective response on the left irrigations, which suggests a hyper response to me.
3. Does anyone have any useful papers/books on causes of hyperfunction/irritative lesions? The pt's history does not fit with Menieres. Pt describes a sudden-onset severe spontaneous episode 6 yrs ago, with motion-provoked symptoms since, in keeping with a stable asymmetry, with the right being the weaker ear. Past history of migraine.
4. Pt also feels dizzy in response to loud noise such as lorries passing - I think this may be a red herring but a VEMP would certainly be interesting. Can any dehiscences increase transfer of heat on caloric and produce a hyper-response?
5. Does anyone have any useful papers on stable irrititative lesions? Can there be a peripheral cause or is this more of a central sign? My search was fruitless so any info would be appreciated.
Sorry to ask so many questions at once!

[Guy]

I can't decide how I feel about the prospect of vestibular hyperfunction.
In general pathologies tend not to lead to increases in sensory sensitivity. If I have a fault with my car it usually doesn't go faster.
Well, I suppose it might if it is the brakes that are faulty.
In neurophysiology the sensory efferents are the brakes, providing inhibition, and if they are not doing their job properly it is easy to see how hypersensitivity can result.
See what a simplistic view I have on life?

In this particular case however, hypersensitivity doesn't come into it.
The presence of the DP to the left has the effect of enhancing the two left-beating responses whilst attenuating the two right beating responses. Without the DP, that warm left result would have been in the region of 50 deg/s and although that's quite high, is less than my upper 95% confidence limit.
If you think about it, one large warm result and three similar, slower, results is exactly what you should expect with an uncompensated peripheral vestibular lesion that has the classic CP & DP combination in opposite directions.
In fact we use that example in this month's Ear & Hearing in our paper on the monothermal caloric test - it explains why the warm monothermal has a much better performance than the cool.
So, an outlier that is greater then its fellows is clinically fine.
An outlier that is less then its fellows is the one to worry about - it may be caused by an ineffective irrigation.

Finally, take no notice of the Chartr software - make your own mind up and don't assume that any software is bullet-proof.
Mind you, there isn't an ENG/VNG system out there that is not without several annoying software glitches.

[Wayne Ellis]

It is interesting to hear your thoughts, Guy. A colleague of mine failed their CAC exam when they had a very similar set of results i.e. one large outlying warm response with a sig CP & DP. The examiner felt that the patient appeared more anxious at this point which may have caused a heightened response and therefore the irrigation should have been repeated (which they did not do).

[Guy]

That is unfortune.
I do hope the CAC candidate (a) appealed the decision and (b) asked the examiners for the reference to a peer reviewed paper giving evidence that there is a link between anxiety and slow phase nystagmus velocity in the caloric test. [Postscript: see the posts below where just such a paper is quoted!]
With the exception of perforating the patient's TM I know of no mechanism whereby a heightened response is produced as the result of an irrigation error.

As a former CAC examiner I would want to probe the candidate's knowledge and seek their justification for their actions (perhaps the examiners did just that) rather than blindly carrying out a procedure without thinking through the implications. However on the face of it I would be happy to accept a large response for the reasons I've given above - it usually fits in with the expected consequences of a combined CP & DP.

[Britney Ears]

Yes, thank you for your reply Guy, and your thoughts Wayne.

The thought had crossed my mind that the LW was a heightened response initially. The RW irrigation had been a poor one with no response and was later repeated. That in effect made the LW the first subjective response, and the patient had been apprehensive about the test as she had had a caloric several years before during her initial acute episode. However she also reacted in the same way to the LC.

This leads me on to my next question - to what extent would anxiety affect the overall caloric result? I have heard it said that the response to the first irrigation is likely to be the greatest. Do people attribute to this to initial anxiety or the physiological adaptation that was once thought to occur? Your IJA paper found that order effects are due to calibration drift, Guy.

I have read that anxiety can increase the VOR gain. However if I was an anxious patient that had a strong and unpleasant response to the first caloric irrigation, I certainly wouldn’t feel calm about the next three! Any thoughts/opinions?

[Guy]

I suspect that the opinion that the first irrigation is greater than subsequent responses has its origin in two genuine observations:

1) there is a definite order effect in the subjective rating of vertigo by the patient that is simply not there if you look at the slow phase velocity as measured by VNG - if four identical results are obtained (in deg/s) the patient is highly likely to judge that magnitude of the induced vertigo declines a testing proceeds - the first is the worst and the last is the mildest. I haven't a clue what the mechanism of this is but my guess is that it occurs at the cortical level;

2) there is indeed a decline in the measured response if you test by ENG without re-calibrating immediately prior to each test, an effect caused by a decline in the corneo-retinal potential during testing.

Both of these are discussed in my IJA paper which concludes that there is no significant physiological adaptation in the vestibular caloric response.

[Britney Ears]

I think we were writing our posts at the same time.....

I came across this paper earlier today;

Effects of anxiety arousal and mental stress on the vestibulo-ocular reflex
YARDLEY L. (1) ; WATSON S. ; BRITTON J. ; LEAR S. ; BIRD J.

Abstract
Although the subjective reports of patients suggest that anxiety may aggravate vertigo and imbalance, there has been little research into how anxiety might directly affect balance system functioning. We conducted two studies to examine the effect of anxiety and arousal on the vestibulo-ocular reflex (VOR). In the first study, pre-test fear ratings were obtained from 20 normal subjects and 36 anxious subjects immediately prior to rotation and caloric testing. Fear ratings were significantly correlated with the maximum slow-phase velocity (SPV) of nystagmus induced by caloric testing. In the second study, we assessed the VOR response to rotation of 36 normal subjects under 3 task conditions : a) minimal alerting (counting backwards during rotation) ; b) physical arousal (induced by exertion prior to rotation) ; c) mental arousal (induced by performance of stressful mental tasks during rotation). Both the physical and mental tasks induced a significant increase in heart rate compared with the alerting condition. The maximum SPV of the nystagmus induced by rotation was significantly greater during performance of the mental task than in the other two conditions. These combined results indicate that anxiety may influence the gain of the VOR.

Acta oto-laryngologica
1995, vol. 115, no5, pp. 597-602 (25 ref.)

I dont have the full text yet. It is the only one I have found on stress and VOR gain.
Poor CAC student - I wouldnt want to repeat an irrigation on a patient if it has made them feel unwell. Poor patient if that examiner had been performing the test! I think there is a limit to how much you should put a patient through on the caloric test. I certainly wouldnt have wanted to repeat any with this pt I saw, seeing as they were groaning on the two left irrigations.

[Britney Ears]

posting simulataneously again.... thank you for clarifiying, I have often wondered about this but could not find an answer I was satisfied with.

Time for the weekend!

[Guy]

Seems I may need to eat my words - not for the first time!

I will need to find this paper and digest before commenting further.
Of particular relevance will be the magnitude of the effect that they observed to see if it can explain the sort of change you (and the CAC candidate) witnessed.
There a difference between statistical significance and clinical importance.
We'll see.
Thanks for the reference.

[Cochlear]

This is watter calloric test.

Left side has usual values, but I would say that right side has more pronaunced values.

Anyway, no spont. Ny.
This pt has no hearing problems. Adg normal (10dB)
Compas walk - drift to right
Dix-Hallpike negative.

History:
no vertigo, but feeling that head tilts backwards. This awkward feeling lasts 1-2 sec. without anyother sy; present few years but intesifies last 6 months.

This pt has the sy of VB insuf., and migraine.

I've red that VB insuf can cause hyperactive response, but could it be just to one side?

Or you would rather interpret this as unilateral weaknes? Any ideas why?

I wait to see MRI and Doppler.

[Cochlear]

MRI OK.

Conclusion:
History and my general impresion sugest Psichogenig vertigo

I still can't explain this 40% assymetry. Please, help.

[AcousticS]

This is really funny.
The patient has no hearing problems. (ABR values confirm this)
If you assume your patient is not pretending but really has problems.
Then it can be valuable only central misfire. What do you do next?

[Cochlear]

I can't decide how I feel about the prospect of vestibular hyperfunction.
In general pathologies tend not to lead to increases in sensory sensitivity. If I have a fault with my car it usually doesn't go faster.
Well, I suppose it might if it is the brakes that are faulty.
In neurophysiology the sensory efferents are the brakes, providing inhibition, and if they are not doing their job properly it is easy to see how hypersensitivity can result.

I agree with you, but I wonder if there are the situations when there is the peripheral pathology with hyperactive response.
In the beginning stage of the Menieres patient can have the Ny to the direction of the involved ear. Also, they usually at that stage have increased VEMP. But can the caloric test give the hyperactive response on that affected ear as well ?

Or when we are talking about the brakes. The flocculus is the brake for vestibular nuclei. Can we have the hyperactive response just on the side of the affected flocculus ? I can't find anything about one side hyperactive response, because it is usually defined as unilateral weakness.

[kelumsanjeewa90]

Dear Guy,
I have only heard about sensory afferents. What are "sensory efferents"? ( this is in the second post of this thread )
p.s.
I am still a student and pardon me if this indicates that I haven't studied Neurology thorough enough.