Aetiology

Viral labyrinthitis is typically associated with a preceding upper respiratory tract infection. Aetiological viral agents include varicella zoster virus, cytomegalovirus, mumps, measles, rubella, and HIV.[6][7] Labyrinthitis has also been associated with autoimmune inner ear disease (e.g., Cogan's syndrome or Behcet's disease).[5]

Bacterial labyrinthitis is associated with acute or chronic otitis media, meningitis, and cholesteatoma (a collection or growth of epidermal and connective tissues within the middle ear). Unlike viral labyrinthitis, the bacterial form may affect both ears simultaneously.[2][8] Potential bacterial causes include Treponema pallidum, Haemophilus influenzae, Streptococcus species, Staphylococcus species, and Neisseria meningitidis.[2] Syphilitic labyrinthitis may follow tertiary neurosyphilis that occurs many years after the primary infection, and is not seen with acute primary or secondary syphilis.[6]

Pathophysiology

Infections arising in the middle ear (otitis media) can spread to the inner ear through the oval or round window. Inflammation or infectious agents can spread from the inner ear into the internal auditory canal. Meningitis can spread to the inner ear through the cochlear aqueduct or the cochlear modiolus.[8] Haematogenous spread of infectious agents through the labyrinthine artery to the stria vascularis is theoretically possible but has not been demonstrated.[8]

Infection in the membranous labyrinth may result in a significant inflammatory response with resultant intraluminal fibrosis and possible ossification (i.e., labyrinthitis ossificans).[9][10][11] Bacterial meningitis is associated with a significant risk of hearing loss.[12] Auditory or vestibular symptoms, or both, may be present in as many as 20% of children with meningitis.[13]

Classification

Types of labyrinthitis

Serous (viral) labyrinthitis:

  • Caused by inflammation of the labyrinth only

  • Typically presents with less severe hearing loss and vertigo than suppurative labyrinthitis; hearing loss often recovers

  • The term vestibular neuritis (i.e., inflammation of the vestibular nerve) is often mistakenly used interchangeably with viral labyrinthitis. Patients with either condition have vertigo and/or disequilibrium, but vestibular neuritis is not associated with hearing loss, whereas patients with viral labyrinthitis have hearing loss due to inflammation of the cochlea and cochlear nerve.

Suppurative (bacterial) labyrinthitis:

  • Follows direct bacterial invasion of the inner ear and therefore is typically unilateral

  • Typically presents with severe to profound hearing loss and vertigo

  • Hearing loss that occurs with suppurative labyrinthitis is typically irreversible.[4]

Meningogenic labyrinthitis:

  • Occurs in the setting of meningitis

  • Typically begins at the basal turn of the cochlea adjacent to the opening of the cochlear aqueduct.

Autoimmune labyrinthitis:[5]

  • Autoimmune conditions (e.g., Cogan's syndrome or Behcet's disease) affecting the labyrinth typically present with bilateral simultaneous or sequential hearing loss and vertigo

  • Can be corticosteroid-responsive, but sometimes progress to bilateral profound hearing loss and vestibular hypo-function.

Labyrinthitis ossificans:

  • Fibrosis of the membranous labyrinth occurs within a few days of acute infection

  • Ossification can occur as early as fibrosis, resulting in complete osseous replacement of the membranous labyrinth

  • Membranous labyrinth can be obstructed in up to 30% of patients with suppurative labyrinthitis.

Syphilitic labyrinthitis:

  • Can follow tertiary neurosyphilis, which occurs many years after primary syphilis infection, and is not seen with acute primary or secondary syphilis[6]

  • Patients can present with progressive hearing loss and pressure- or sound-induced vertigo (Hennebert and Tullio signs).

HIV-associated labyrinthitis:

  • A variety of auditory and vestibular complaints, including labyrinthitis, have been reported in patients with AIDS. The relative importance of the HIV infection itself as opposed to its associated opportunistic infections requires further study.

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