Electrocochleography is performed in a 40-year-old woman with episodic vertigo, fluctuant low-frequency sensorineural hearing loss, and aural fullness. The summating potential to action potential amplitude ratio (SP/AP ratio) most supportive of endolymphatic hydrops is:

• A Greater than 0.4 ✓
• B 0.1 to 0.2
• C Less than 0.1
• D Exactly 0.3 in all ears regardless of pathology

Explanation

Endolymphatic hydrops distorts the basilar membrane, enlarging the summating potential relative to the action potential. An SP/AP ratio greater than 0.4 (some centers use 0.5) is taken as evidence of hydrops in Meniere disease. Normal ears show ratios around 0.1 to 0.3. Electrocochleography is particularly useful when the diagnosis is uncertain because it can be recorded during or shortly after an attack, when the ratio is highest.

Reference: Glasscock-Shambaugh, Surgery of the Ear, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.