## Diagnostic Investigations in Meniere Disease **Key Point:** Electrocochleography (ECoG) is the most sensitive and specific non-invasive test for confirming endolymphatic hydrops in Meniere disease. ### Electrocochleography (ECoG): Mechanism ECoG measures electrical potentials generated by the inner ear: - **Summating Potential (SP):** reflects displacement of the basilar membrane and cochlear partition - **Action Potential (AP):** reflects neural activity of the cochlear nerve **In endolymphatic hydrops:** - Increased endolymphatic pressure displaces the basilar membrane - **SP/AP ratio becomes abnormally elevated** (normal: <0.4; abnormal: >0.5) - This is pathognomonic for endolymphatic hydrops **High-Yield:** An elevated SP/AP ratio >0.5 is the electrophysiological hallmark of Meniere disease and can be present even when audiometry is normal. ### Comparison of Investigations | Investigation | Sensitivity | Specificity | What It Shows | Diagnostic Value | |---|---|---|---|---| | **ECoG** | 75–90% | 85–95% | Endolymphatic hydrops directly | Gold standard | | **Pure tone audiometry** | High | Low | Low-frequency SNHL (non-specific) | Supportive only | | **Caloric testing** | Variable | Low | Vestibular hypofunction | Non-specific | | **MRI with gadolinium** | 65–75% | 85% | Hydrops (research tool) | Emerging alternative | | **CT temporal bone** | N/A | N/A | Excludes osseous pathology | Rule-out only | **Clinical Pearl:** ECoG can be abnormal in the asymptomatic ear of a unilateral Meniere patient, suggesting subclinical bilateral disease. ### Why ECoG is Gold Standard 1. **Direct measurement** of endolymphatic pressure effects 2. **Objective and reproducible** electrical recording 3. **Can be abnormal before** audiometric changes 4. **Guides prognosis** — persistent elevation suggests ongoing hydrops [cite:Dhingra ENT 8e Ch 9; Paparella & Shumrick Otolaryngology 3e] 
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