Introduction

• Pathological processes in the peripheral receptors in the inner ear and of the vestibular branch of the VIII cranial nerve.
• Cause: includes otitis interna, canine geriatric vestibular disease, aminoglycoside toxicity, topical iodophors or chlorhexidine, hypothyroidism, neoplasia, trauma (especially iatrogenic) and congenital peripheral vestibular disease.
• Signs:
  • Head tilt.
  • Wide base stance.
  • Ataxia with a tendency to lean to one side.
  • Circling and nystagmus.
  • Deafness and disturbances of balance occur together.
  • Important to differentiate these disorders from central vestibular disturbances.
• Diagnosis: signs.
• Treatment: none
• Prognosis: good to guarded.

Pathogenesis

Etiology

• Autosomal inheritance in congenital peripheral vestibular disease.
• Immune-mediated disease.
• Transitory labyrinthitis.
• Endolymphatic fluid dynamic abnormality within labyrinthine organ.
• Neuritis of the vestibular portion of facial nerve VIII.
• Metabolic, ie hypothyroidism.
• Foreign body related.
• Secondary to nasopharyngeal polyps.
• Extension of opportunistic infection byStaphylococcusspp,Streptococcusspp,P. canis,Clostridium welchiiand especiallyPseudomonas aeruginosa.
• Neoplasia.
• Head trauma (rare).

Geriatric vestibular disease

• Results from abnormal flow of endolymphatic fluid in the semicircular canals of the inner ear secondary to either:
  • Disturbance in production, circulation or absorption of the fluid.
  • Intoxication of vestibular receptors and inflammation of the vestibular nerve.

Iatrogenic damage during the treatment of middle ear disease

• Trauma from excessive pressure from overzealous irrigation.
• Use of ototoxic compounds in irrigation of middle ear.

Sudden onset idiopathic otitis interna

• Extension of an infection of the external ear through either the tympanic membrane or the oral and nasopharyngeal cavities via the eustachian tubes.
• Hematogenous spread of infectious agent, possibly a virus.
• Hematogenous spread of a systemic infection.
• See under otitis interna Otitis interna , canine geriatric vestibular disease, metronidazole toxicity, aminoglycoside toxicity, neoplasia, trauma (especially iatrogenic) and congenital peripheral vestibular disease.

Predisposing factors

• Old dogs.
• Dogs which are prone to otitis externa, ie the German Shepherd dog, dogs with pendulous or hairy ears, dogs with generalized skin conditions (especially atopy).

• Hypothyroidism.

• Inhalant anesthesia may change the pressure of the middle ear and predispose to infection.

Specific

• Otitis media.
• Bulla irrigation or bulla osteotomy.

Pathophysiology

• See under otitis interna Otitis interna , canine geriatric vestibular disease, metronidazole toxicity, aminoglycoside toxicity.

• Space occupying lesion → pressure on surrounding nervous tissue → compromised blood supply and anoxia of nervous tissue or direct pressure trauma to nervous tissue → loss of function.

• Autosomal recessive inheritance → non-inflammatory neuroepithelial degeneration of the cochlea with a progressive loss of auditory sensory hair cells → almost complete loss of organ of Corti by 11 weeks of age → bilateral, severe, permanent deafness and vestibular signs which improve as dog learns to compensate.

• Lymphocytic labyrinthitis (otitis interna) → multiple lymphocytic aggregates in the lamina.
• Multiple lymphocytic aggregates in the lamina propria underneath the ciliated columnar epithelium of the inner ear → loss of function, deafness and vestibular signs.

Timecourse

• Usually acute onset - may occur over several hours.

Diagnosis

Treatment

Prevention

Outcomes