During bithermal caloric testing with water at 30 degrees C and 44 degrees C, a patient shows reduced responses on irrigating the left ear only, with normal responses on the right. This pattern indicates:

• A Left directional preponderance suggesting a central lesion
• B Normal study, as asymmetry up to 40 percent is physiological
• C Bilateral vestibular failure
• D Left canal paresis, indicating a peripheral lesion of the left labyrinth or vestibular nerve ✓

Explanation

Canal paresis means reduced response from one side regardless of water temperature, localising the lesion to the ipsilateral lateral semicircular canal, its ampulla, or the superior vestibular nerve. Directional preponderance is a different abnormality where nystagmus in one direction exceeds the other and suggests a central or velocity storage disturbance. Asymmetry above about 20 to 25 percent is pathological, so a 40 percent cutoff is wrong. The caloric test selectively assesses the lateral canal.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.