Electrocochleography (ECochG) in Meniere's disease classically shows elevation of which ratio, and what does this indicate?
- A Wave I–V interaural latency ratio greater than 0.3 ms, indicating retrocochlear disease
- B Acoustic reflex decay ratio greater than 50%, indicating superior canal dehiscence
- C Summating potential to action potential (SP/AP) ratio greater than 0.4, indicating endolymphatic hydrops ✓
- D Cochlear microphonic to compound action potential ratio greater than 2, indicating auditory neuropathy
Correct answer: C. Summating potential to action potential (SP/AP) ratio greater than 0.4, indicating endolymphatic hydrops
Explanation
Electrocochleography (ECochG) measures cochlear and eighth nerve electrical potentials. In Meniere's disease (endolymphatic hydrops), the Summating Potential (SP) — generated by outer hair cell displacement — is abnormally enlarged relative to the Action Potential (AP). An SP/AP ratio >0.4 (some use >0.45 or >0.5) is considered abnormal and supports the diagnosis of endolymphatic hydrops. The elevated SP reflects the distortion of basilar membrane mechanics due to increased endolymph volume. Wave I–V latency ratios are retrocochlear markers on ABR.
Reference: Dhingra Diseases of Ear, Nose and Throat, 7th ed.
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Written and medically reviewed by the StethoPrep medical team.