During bithermal caloric testing, warm water at 44 degrees Celsius is irrigated into the right external auditory canal of a patient with an intact tympanic membrane and normal vestibular function. The expected response is:

• A Horizontal nystagmus with the fast phase toward the right ✓
• B Horizontal nystagmus with the fast phase toward the left
• C Torsional nystagmus with the fast phase toward the left
• D Vertical upbeat nystagmus

Explanation

Caloric responses follow the mnemonic COWS: Cold Opposite, Warm Same. Warm water creates a mild thermal convection current in the lateral semicircular canal that mimics ampullopetal (excitatory) endolymph flow, increasing ipsilateral firing and driving the eyes slowly toward the opposite side with a corrective fast phase toward the irrigated ear. Hence warm water on the right gives a right-beating nystagmus. Option B would be correct only for cold water on the right side.

Reference: Dhingra's Diseases of Ear, Nose and Throat, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.