Introduction

• Cause: most commonly infection via middle ear also through hematogenous spread or ascending infection through the Eustachian tube.
• Signs: head tilt, circling and nystagmus (vestibular syndrome).
• Deafness and disturbances of balance occur together.
• Facial nerve and sympathetic trunk can be involved in middle ear. Virtually always unilateral.
• Diagnosis: history, clinical signs, neurological assessment, advanced diagnostic imaging (MRI, CT).
• Treatment: broad-spectrum antibiotics initially, then based on cytology and bacterial culture of material collected on myringotomy where possible. 
• Important to differentiate this disorder from central vestibular dysfunction.
  Print off the owner factsheet on Chronic otitis to give to your client.

Pathogenesis

Etiology

• Infection most commonly as an extension of infection from the middle ear in acute cases by Staphylococcus spp Staphylococcus spp and Streptococcus spp Streptococcus spp, and in chronic cases Pseudomonas aeruginosa Pseudomonas aeruginosa.
• Iatrogenic: use of ototoxic compounds within the middle ear either cleaning solutions or medication. Administration of systemic drugs with ototoxic effects.
• Idiopathic form: hematogenous spread of infectious agent, possibly viral.
• Trauma to head (rare).

Predisposing factors

General

• Most common primary cause of otitis externa is allergy. Breeds prone to allergy are the most likely to develop otitis media/interna.
• Prediposing factors for otitis include conformation (dogs with pendulous or hairy ears) and life style (swimming dogs), these increase an animal risk of developing disease if a primary cause is present.

Specific

• Otitis media Otitis media.
• Bulla irrigation or bulla osteotomy Bulla osteotomy.

Pathophysiology

• Inner ear disease:
  • Damage to cochlea:
    • Sensory nerve endings within the cochlea damaged by infection or ototoxins which can be spread hematogenously (especially systemic drugs) or diffuse through the cochlear window leading to deafness.
  • Damage to vestibular apparatus:
    • Vestibular system consists of proprioceptors (saccule, utricle and semicircular canals) within the inner ear (petrosal temporal bone), the vestibular nerve (VIII), four brainstem nuclei and the cerebellum. Peripheral vestibular dysfunction (PVD) is as a result of damage to structures with the petrosal temporal bone. Central vestibular dysfunction (CVD) is due to damage to structures in the brain stem and cerebellum.
    • PVD most commonly extension of otitis externa/otitis media where either infection or ototoxins spread hematogenously (especially systemic drugs) or diffuse through the cochlear window into the inner ear to damage the vestibular apparatus. Infection and toxins within the middle ear may also lead to facial nerve paralysis Facial nerve neuropathies and partial or complete Horner's syndrome Horner's syndrome on affected side.

Other trigger factors

• Head trauma → damage to round cochlear window → leakage of perilymph from semicircular canals.

Diagnosis

Treatment

Prevention

Outcomes