labyrinthitis

**Definition:** Inflammation of the inner ear's membranous labyrinth, involving both the vestibular (semicircular canals, utricle, saccule) and cochlear structures. Vestibular neuritis = vestibular nerve only (no hearing symptoms).

**Etiology:** - Viral (most common): often follows URI; implicated agents include HSV-1, VZV (Ramsay Hunt syndrome/herpes zoster oticus), CMV, influenza, measles, mumps, rubella, adenovirus, enteroviruses. - Bacterial (serous vs suppurative): complication of acute or chronic otitis media, cholesteatoma, or bacterial meningitis (S. pneumoniae, H. influenzae). Suppurative labyrinthitis can cause permanent, profound hearing loss. - Other: autoimmune (e.g., Cogan syndrome, granulomatosis with polyangiitis), syphilis, post-surgical or traumatic (temporal bone fracture), toxic.

**Pathophysiology:** Inflammation and edema of the labyrinth reduce firing from the affected vestibular apparatus. This creates asymmetric tonic input between the two sides. The brain interprets the asymmetry as head rotation, producing vertigo, nystagmus, and nausea/vomiting. Cochlear involvement causes sensorineural hearing loss and tinnitus.

**Clinical presentation:** - Acute-onset severe, continuous vertigo lasting days (gradually improves over days to weeks) - Nausea/vomiting, gait imbalance (falls toward the affected side) - Unilateral sensorineural hearing loss and/or tinnitus (the key differentiator) - Horizontal (or horizontal-torsional) nystagmus, **unidirectional**, fast phase **away** from the affected ear, which beats more with gaze away from the lesion (Alexander's law) - Positive head impulse test (corrective saccade when the head turns toward the affected side) - No skew deviation, no central signs

**Diagnosis:** Primarily clinical. Use the HINTS exam (Head Impulse abnormal, Nystagmus unidirectional/horizontal, Test of Skew negative) to distinguish peripheral from central causes (e.g., posterior circulation stroke). Audiometry shows sensorineural hearing loss. MRI (with gadolinium) is used if central causes are suspected, if there are atypical features, or for complications. A danger sign is any new neurological deficit, which suggests central etiology (stroke, e.g., AICA infarct, which also causes sudden hearing loss and vertigo with facial paralysis).

**Management:** - Viral: supportive. Short course of vestibular suppressants (meclizine, benzodiazepines, antiemetics) for the first 24–72 h only, since prolonged use impairs central compensation. Early vestibular rehabilitation. Corticosteroids are sometimes used (especially for hearing loss). Antivirals (acyclovir/valacyclovir) + steroids for VZV (Ramsay Hunt). - Bacterial: IV antibiotics, with possible surgical drainage (e.g., tympanostomy, mastoidectomy) for the underlying infection.

**Complications:** Permanent sensorineural hearing loss, chronic imbalance, labyrinthitis ossificans (after suppurative disease, with fibrosis/calcification), meningitis spread, and BPPV after labyrinthitis.

**Differentials (high-yield comparison):** - **Vestibular neuritis:** vertigo for days, NO hearing loss - **Ménière disease:** episodic vertigo (20 min to hours), fluctuating low-frequency SNHL, tinnitus, aural fullness; endolymphatic hydrops - **BPPV:** brief (<1 min) positional vertigo, Dix-Hallpike positive, no hearing loss - **Acoustic neuroma (vestibular schwannoma):** gradual unilateral SNHL, tinnitus, CN VIII (+/- CN V, VII); NF2 if bilateral - **Central causes (cerebellar/brainstem stroke):** HINTS central pattern, direction-changing nystagmus, other neuro deficits - **Perilymphatic fistula:** vertigo/hearing loss after trauma or barotrauma, positive fistula (Hennebert) sign

**Board pearls:** "Acute vertigo + hearing loss + recent URI" = labyrinthitis. "Acute vertigo without hearing loss" = vestibular neuritis. Vesicles in the ear canal/auricle plus facial palsy plus vertigo/hearing loss = Ramsay Hunt syndrome (VZV). Otitis media or meningitis with new hearing loss/vertigo = suppurative labyrinthitis.