Caloric testing – Case study 11 question 5

[Kirstin Kucera]

Can someone explain why the answer to this question is “Decreased left-beating nystagmus when the right ear is irrigated with cold water” instead of “Decreased left-beating nystagmus when the right ear is irrigated with warm water”? The last 2 sentences of the explanation seem contradictory: “This means that cold water/air induces nystagmus to the opposite side of the irrigated ear and warm water/air induces nystagmus to the same side as the irrigated ear. Therefore, we would expect this patient to have decreased nystagmus to the left when the right ear is irrigated with cold water/air and decreased nystagmus to the right when the right ear is irrigated with warm water/air.”

[Masato Kobayashi]

Hi Kristin! This references back to the mnemonic COWS (Cold-Opposite, Warm-Same). Cold and warm water will induce different patterns of nystagmus due to the inhibition and excitation of the vestibular system, respectively. “Decreased left-beating nystagmus when the right ear is irrigated with warm water” is incorrect because introduction of warm water would induce right-beating nystagmus not left-beating nystagmus. And in the case of this patient with a right hypofunction, a reduced right-beating nystagmus compared to a normal reference point would be observed. Hopefully that clarified your question – happy to expand!

[Christina Arrechavala]

“This means that cold water/air induces nystagmus to the opposite side of the irrigated ear and warm water/air induces nystagmus to the same side as the irrigated ear.”

So if the R ear is irrigated with cold water, we would expect L (opposite side) nystagmus, if the R ear is irrigated with warm water, we would expect R (same side) nystagmus.

“Therefore, we would expect this patient to have decreased nystagmus to the left when the right ear is irrigated with cold water/air and decreased nystagmus to the right when the right ear is irrigated with warm water/air.”

This is saying the same thing but adding in that it is a decreased nystagmus. This is because this test normally produces nystagmus following the COWS saying. If there is a uniliateral vestibular hypofunction, then the normally produced nystagmus would be lessened due to HYPOfunction.

Therefore the correct answer would be:
“Decreased left-beating nystagmus when the right ear is irrigated with cold water” as cold water causes opposite nystagmus (R irrigation causes L nystagmus)

The answer you chose is incorrect because it is stating a contralateral nystagmus was occurring with a stumulant that should have caused an ipsilateral nystagmus. Warm water would cause same side nystagmus, so it would be RIGHT beating nystagmus, not left, as the right ear was irrigated.

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