VARIANT CALORIC TESTS

Timothy C. Hain, MD • Page last modified: March 7, 2021See parent page: caloric_test.

 

It is tempting to adopt a variant caloric test to save time, reduce health care costs, or reduce patient discomfort, and reduce the risk of emesis. The bottom line is DON'T DO IT. Either do it "right", or don't do it at all. Here is the rationale.

Variant caloric tests: Basically there is just one good way to do it (bithermal and ice is needed), and a lot of not so good ways.

caloric test

There are several variant caloric tests, but at present, the standard is the water bithermal caloric test. This consists of 4 sections 2 ears * 2 temperatures (warm and cold). Ideally this is done with warm and cold water. The method is discussed on the main caloric page.

Air calorics

Calorics can also be done with air, and although not as messy, the results are not as reliable. We suggest avoiding air calorics. Zapala et al (2008) suggested that air and water were similar, "when calibrated as described therein". Perhaps this worked for them, but our observations of community air calorics is that they are often sources of false positives. Or in other words, it is possible to do as good a job with air as with water, but most labs cannot pull it off.

Air calorics are used for several reasons - -they CAN be used in a perforated ear (unlike water), they are not as messy, and they are also not as stimulating (i.e. less risk of emesis). That being said, we suggest avoiding them, and using the alternatives mentioned below.

Although air (unlike water) can be used to test a perforated ear, the accuracy is very questionable as it depends on the size of the hole in the ear drum. If the hole is large, air can get into the middle ear and produce paradoxical responses. If the hole is small, probably it is OK, but we don't think it is reasonable to take a chance that the technician doing the caloric will be able to judge whether or not the results can be trusted based on the size of the perforation. We think that the spontaneous, head-shaking, and vibration tests are a reasonable alternative in this situation. Or in other words, do the VENG including spontanoues, head-shaking and vibration, but leave out the caloric part.

If available, the rotatory chair and VHIT tests offer similar information, whether the ear is perforated or not. We suggest avoiding air calorics in perforated ears as well.

Monothermal caloric test:

Monothermal 100
Monothermal caloric -- 100 cc stimulus. We strongly advise against doing this, see below.

The monothermal caloric test is a variant caloric method in which a single large bolus (i.e.100 cc) of a single large bolus of ice water is given, and compared to a smaller bolus (i.e. 10 cc), rather than two irrigations with hot and cold (Kumar, 1981).. We advise against doing the monothermal test. When mismatched irrigation volumes are used, as in the monothermal test, there is no averaging of data and thus there is lower accuracy. Another problem is that the "strong" stimulus -- 100 cc of 0 deg centigrade water (from the fridge), can provoke a gigantic response and make the patient very sick. Finally, the rationale of comparing 10 cc to 100 cc is questionable. Adams et al (2016) concluded that "Accuracy of the MCST is lacking precisely where it is needed most-at the border of normal and abnormal vestibular function. "

Another variant of the monothermal test is to cut corners even more, and do just half of the work -- the idea is that if you get strong and equal responses from both sides, you can just do 2 irrigations, and leave out the other two. This is both monothermal and it also cuts out half of the irrigations. This saves time, and a very small amount of money (because insurance pays very little for caloric testing anyway). Thatcher et al (2016), suggested that this saved $264/patient. We are puzzled where Thatcher got this number as we are not fortunate enough to be reimbursed at this rate in Illinois for half of our caloric testing procedure. Perhaps this is relevant in hospital settings though. Thatcher found that "Using a monothermal interear difference threshold of 25%, warm monothermal screening had sensitivity of 98.0%, specificity of 91.3%, false negative rate of 2%, and false positive rate of 8.7%. Cool monothermal screening also had excellent sensitivity (92.3%) and specificity (95.3)%, with a false negative rate of 7.7%, and a false positive rate of 4.7%. " We think that Enticott's conclusion is more reasonable," ... unacceptably high false-positive rates were produced reflecting more than 3/4 of normal BT results failing the MT criterion. " (Enticott et al, 2003)

Bilateral irrigation test

In the bilateral irrigation test, both ears are irrigated at the same time. This procedure is faster and results in much less dizziness than the variants where air or water are done one at a time, but it "throws away" the total response parameter, as well as any clue as to whether the stimulus reached the inner ear. For this reason, it is rarely encountered. Bilateral irrigation sacrifices too much for speed. On the other hand, Sataloff et al (2017) reported that simultaneous binaural testing was superior to conventional alternative bithermal caloric testing. We are dubious. Furman et al (1988) commented that "Using receiver-operator characteristic methodology, it was found that the ability of the alternate test to distinguish between a healthy population and a patient population was superior to that of the simultaneous test. " In other words, while quicker, it is not as accurate as standard testing.

Balloon test

Here a balloon filled with cold or warm water is placed in the external ear canal, as shown below.

Balloon caloric
Balloon version of caloric (one of the variant caloric tests, see below.) We strongly advise against doing this.

When water is not used directly, as in the balloon test, heat or cold is not conducted as efficiently to the ea, we think it is imprudent to adopt more convenient but less accurate methodology using balloons.

Summary of variant caloric tests:

Because of the considerable inaccuracy even for the best of the lot, the bithermal water method, we think that laboratories should stick to the standard method -- the bithermal binaural caloric test. This should be supplemented by ice when there is no response.

We do not think that it is prudent to reduce the number of irrigations to save money or time. Our thought is it is best to do it right or don't do it at all, possibly substituting the rotatory chair test or VHIT test, should caloric irrigation not be done.

 

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