Cervical VEMP (cVEMP) is performed in a patient suspected of superior canal dehiscence syndrome (SCDS). What response pattern is expected in SCDS compared to normal?

• A Absent cVEMP on the affected side
• B Reduced cVEMP amplitude on the affected side
• C Prolonged latency of P1-N1 complex on the affected side
• D Enhanced (larger) cVEMP amplitude and lower threshold on the affected side ✓

Explanation

In superior canal dehiscence syndrome (SCDS), the bony covering over the superior semicircular canal is absent or thin, creating a third mobile window into the inner ear. This lowers the acoustic impedance of the vestibular system, making the saccule (which mediates cVEMP) hypersensitive to sound. Consequently, cVEMP shows increased amplitude and a lower threshold (often <85 dB HL) on the affected side compared to normal (threshold >95 dB HL). Ocular VEMP (oVEMP) typically shows enhanced N1-P1 amplitude as well. This enhanced cVEMP with low threshold is diagnostically specific for SCDS.

Reference: Dhingra Diseases of Ear, Nose and Throat, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.