A 34-year-old woman from Delhi presents with sudden-onset hearing loss in the left ear for 3 days, accompanied by tinnitus and mild vertigo. She reports a recent upper respiratory tract infection 1 week prior. On examination, Weber test lateralizes to the right ear, and Rinne test shows air conduction better than bone conduction in both ears. Otoscopy is normal. Audiometry reveals a left-sided sensorineural hearing loss across all frequencies with a 3 dB air-bone gap. What is the most likely diagnosis?

Explanation

## Clinical Analysis **Key Point:** Sudden sensorineural hearing loss (SSNHL) is a medical emergency defined as ≥30 dB loss in ≥3 consecutive frequencies over ≤72 hours. Viral labyrinthitis is a common etiology. ### Diagnostic Criteria for SSNHL | Criterion | Present in This Case? | |-----------|----------------------| | **Onset** | Sudden (3 days) ✓ | | **Type** | Sensorineural (AC > BC) ✓ | | **Laterality** | Unilateral (left ear) ✓ | | **Associated symptoms** | Tinnitus, vertigo ✓ | | **Recent viral illness** | URTI 1 week prior ✓ | | **Otoscopy** | Normal ✓ | | **Air-bone gap** | <5 dB (pure SNHL) ✓ | ### Why This Is SSNHL from Viral Labyrinthitis 1. **Temporal pattern:** Sudden onset over 3 days fits SSNHL definition; rules out gradual presbycusis or otosclerosis. 2. **Unilateral SNHL:** Weber lateralizes to the unaffected (right) ear; Rinne confirms air conduction > bone conduction (SNHL pattern). 3. **Associated vestibular symptoms:** Vertigo and tinnitus suggest viral labyrinthitis affecting both cochlear and vestibular divisions of CN VIII. 4. **Recent viral prodrome:** URTI 1 week prior is a classic trigger for viral labyrinthitis and SSNHL. 5. **Normal air-bone gap (3 dB):** Confirms pure sensorineural loss; excludes middle ear pathology. 6. **Normal otoscopy:** Rules out acute otitis media or Eustachian tube dysfunction. **High-Yield:** **SSNHL = sudden onset SNHL + normal otoscopy + often preceded by viral illness.** Viral labyrinthitis is the presumed mechanism in ~50% of idiopathic SSNHL cases. **Mnemonic: SSNHL Red Flags** — **SUDDEN**: Onset ≤72 hours; **UNILATERAL**: One ear only; **NORMAL**: Otoscopy and tympanometry; **DIZZINESS/TINNITUS**: Vestibular or cochlear involvement; **EMERGENCY**: Requires urgent audiometry and corticosteroids within 2 weeks. ### Pathophysiology of Viral Labyrinthitis Viral infection (commonly enterovirus, HSV, VZV) causes inflammation of the membranous labyrinth, leading to: - Cochlear hair cell damage → sensorineural hearing loss - Vestibular end-organ inflammation → vertigo and nystagmus - Endolymphatic hydrops → tinnitus **Clinical Pearl:** SSNHL is a medical emergency. Audiometry must be performed within 2 weeks, and corticosteroids should be initiated urgently (within 2 weeks of onset, ideally within 72 hours) to maximize recovery. ### Differential Exclusions ```mermaid flowchart TD A[Sudden unilateral hearing loss]:::outcome --> B{Air-bone gap?}:::decision B -->|Present| C[Conductive loss]:::outcome C --> D[Acute otitis media<br/>ETD<br/>Hemotympanum]:::outcome B -->|Absent| E[Sensorineural loss]:::outcome E --> F{Otoscopy normal?}:::decision F -->|No| G[Perilymphatic fistula<br/>Temporal bone fracture]:::outcome F -->|Yes| H{Vestibular symptoms?}:::decision H -->|Yes| I[Viral labyrinthitis<br/>Acoustic neuroma<br/>Stroke]:::outcome H -->|No| J[Idiopathic SSNHL<br/>Autoimmune SNHL]:::outcome ``` - **Acute otitis media:** Would show conductive loss with air-bone gap (20–30 dB), otoscopic findings (erythema, fluid level, perforation), and fever. No vertigo. - **Otosclerosis:** Conductive or mixed loss with air-bone gap; gradual onset over months–years, not sudden; no vertigo or recent viral illness. - **Eustachian tube dysfunction:** Conductive loss with air-bone gap; no sensorineural component; no vertigo or tinnitus.