A 38-year-old woman presents with sudden-onset hearing loss in the left ear for 2 days, associated with vertigo and tinnitus. She denies ear discharge or trauma. On examination, Weber test shows lateralization to the right ear, and Rinne test shows air conduction better than bone conduction in the left ear. Otoscopy is normal. Audiometry reveals a unilateral sensorineural hearing loss in the left ear across all frequencies. MRI of the internal auditory canal is normal. What is the most likely diagnosis?

Explanation

## Diagnosis: Idiopathic Sudden Sensorineural Hearing Loss (SSNHL) ### Clinical Presentation **Key Point:** Sudden sensorineural hearing loss (SSNHL) is defined as ≥30 dB hearing loss at ≥3 consecutive frequencies occurring over ≤3 days. Idiopathic SSNHL accounts for ~90% of cases when other causes are excluded. This patient meets diagnostic criteria: - **Acute onset:** 2 days (within the ≤3-day window) - **Sensorineural pattern:** Air conduction > bone conduction on Rinne test - **Unilateral:** Left ear only - **Associated symptoms:** Vertigo and tinnitus (common in SSNHL) - **Normal otoscopy:** Excludes conductive pathology - **Normal MRI:** Rules out retrocochlear lesions (acoustic neuroma) ### Pathophysiology of SSNHL Multiple proposed mechanisms (no single etiology proven): 1. **Viral labyrinthitis** — most widely accepted theory 2. Vascular insufficiency to the cochlea 3. Autoimmune inner ear disease 4. Perilymphatic fistula 5. Idiopathic cochlear inflammation **Mnemonic: SSNHL Causes — VIA (Viral, Ischemic, Autoimmune)** ### Diagnostic Workup Algorithm ```mermaid flowchart TD A[Sudden hearing loss]:::outcome --> B{Otoscopy normal?}:::decision B -->|No| C[Conductive cause]:::outcome B -->|Yes| D{Sensorineural pattern<br/>on Rinne/Weber?}:::decision D -->|No| E[Mixed or conductive]:::outcome D -->|Yes| F{Unilateral or bilateral?}:::decision F -->|Bilateral| G[Autoimmune SNHL<br/>or systemic disease]:::outcome F -->|Unilateral| H{MRI IAC normal?}:::decision H -->|Abnormal| I[Acoustic neuroma<br/>or retrocochlear lesion]:::urgent H -->|Normal| J[Idiopathic SSNHL]:::action J --> K[Corticosteroids<br/>within 2 weeks]:::action ``` ### Differential Diagnosis Table | Feature | Idiopathic SSNHL | Acoustic Neuroma | Serous Otitis | Otosclerosis | | --- | --- | --- | --- | --- | | Onset | Acute (hours–days) | Insidious (weeks–months) | Gradual | Gradual (months–years) | | Pattern | Unilateral, flat or sloping | Unilateral, high-frequency | Bilateral or unilateral | Often unilateral, low-freq | | Vertigo | Often present | Rare (unless large) | Rare | Rare | | Tinnitus | Common | Common | Uncommon | Common | | Otoscopy | Normal | Normal | Normal (may see fluid level) | Normal | | Rinne | AC > BC | AC > BC | BC > AC (conductive) | BC > AC (mixed) | | MRI IAC | Normal | Abnormal (mass) | Normal | Normal | | Air-bone gap | <10 dB | <10 dB | >20 dB | >20 dB | **High-Yield:** MRI is essential to rule out retrocochlear lesions (acoustic neuroma) in all cases of unilateral SSNHL, even if clinical suspicion is low. ### Management of Idiopathic SSNHL **Clinical Pearl:** Corticosteroids are the only evidence-based treatment; efficacy is highest when started within 2 weeks of onset. 1. **Corticosteroids** (first-line): - Oral prednisone 1 mg/kg/day (max 80 mg) × 5–7 days, then taper - OR intratympanic dexamethasone if oral contraindicated - Best outcomes if started within 2 weeks 2. **Supportive care:** - Vestibular rehabilitation (if vertigo present) - Hearing aids (if permanent loss) - Counseling 3. **Avoid:** - Diuretics (may worsen inner ear fluid dynamics) - Ototoxic drugs **Warning:** Do NOT delay MRI to start treatment — imaging should be done urgently (within 2–4 weeks) to exclude retrocochlear pathology. ### Prognosis - Spontaneous recovery: 30–50% of untreated cases - With corticosteroids: 60–70% recovery rate - Factors predicting poor prognosis: - Age >60 years - Severe initial hearing loss (>90 dB) - Vertigo present - Delayed treatment (>2 weeks) [cite:Dhingra's Diseases of Ear, Nose and Throat 8e Ch 8; Harrison 21e Ch 30]