Contributors: Kyle Braund, Sue Paterson

 Species: Canine   |   Classification: Diseases

Introduction Pathogenesis Diagnosis Treatment Outcomes Further Reading

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.

Presenting Signs

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

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

Presenting Problems

  • Vestibular syndrome.

Client History

Clinical Signs

  • Otitis interna usually presents with signs of PVD.
  • Head tilt, affected side down.
  • Circling towards affected side.
  • Horizontal nystagmus, fast component away from affected side and not affected with head position.
  • Rolling/falling to affected side.
  • Unilateral deafness present. Deafness: acquired, detectable by Brainstem auditory evoked response (BAER) testing at specialist center Hearing tests.
  • Positional ventral strabismus in ipsilateral eye.
  • Vomiting Vomiting.
  • General dullness and inappetence.
  • Unilateral facial paralysis Facial nerve neuropathies, involving upper and lower face but only with concurrent otitis media.
  • When held up vertically, body hangs straight down.
  • Concurrent otitis externa Skin: otitis externa +/- otitis media Otitis media.
  • General dullness and inappetence.
  • Partial or complete Horner's syndrome Horner's syndrome: miosis (small pupil), slight ptosis (drooping upper eyelid), enopthalmos (sunken eye), protrusion of third eyelid, conjunctival flare.
  • Hemifacial spasm on affected side.

Auroscopic examination where the disease is an extension of otitis

  • Otitis externa Skin: otitis externa.
  • Ruptured eardrum in many cases although ear drum can heal in the presence of otitis media.
  • Purulent aural discharge.

Full neurological examination

  • Necessary to differentiate from CVD.
  • Peripheral vestibular lesions head tilt, ataxia Ataxia. Horizontal nystagmus with quick phase away from side of lesion. With central lesions, positional and vertical nystagmus may be present, ie direction is altered with head position.
  • Central vestibular lesions, paresis and reduction or absence of proprioception can occur in the ipsilateral limbs. There may also be evidence of multiple cranial nerve involvement (Deficits V to X11).

Diagnostic Investigation

Radiography

  • Only useful in chronic cases of otitis media where advanced change is present.
  • To diagnose chronic otitis media Otitis media.
  • Absence of normal air shadow in tympanic bulla.
  • Diffuse thickening of bulla wall.
  • Bony destruction and gross bony proliferative changes in the bulla.
  • Gross bony proliferative changes with involvement of the temporomandibular joint.
  • Computed tomography Computed tomography: head: more sensitive for investigation of middle and inner ear disease than radiography.
  • Magnetic resonance imaging: considered the imaging test of choice to investigate intracranial cases of vestibular dysfunction and inner ear disease.
  • Brainstem auditory-evoked response (BAER) Hearing tests: evidence of hearing loss.

Other

  • Examination under anesthesia:
    • Where disease extends from the external ear canal - eardrum rupture identified by palpation with blunt needle or probe Otitis media.
    • Eustachian tube not patent.
      Only test for Eustachian tube patency when a cuffed endotracheal tube is in place

Bacteriology

  • Microbiology:
    • Bacteriology Bacteriology and sensitivity of aural discharge from external ear canal unlikely to reflect bacterial infection in inner ear. Sample from the middle ear taken with a guarded swab or via myringotomy Myringotomy of middle ear or by ear flush with sterile saline more useful.

Differential Diagnosis

Peripheral vestibular syndrome

Central vestibular syndrome

Treatment

Standard Treatment

  • All of: Broad-spectrum, bacteriocidal antibiosis initially but where possible they should be based on cytology and culture and sensitivity of material collected from the middle ear by myringotomy Myringotomy. Drugs usually needed for 6-8 weeks.
  • Where possible choose drugs with good penetration into bone and use towards high end of dose rate. Cocci on cytology: cephalexin Cefalexin or clindamycin Clindamycin. Rods on cytology: enrofloxacin Enrofloxacin or marbofloxacin Marbofloxacin.
  • And: Oral corticosteroids (prednisolone Prednisolone).
  • And: Analgesic (gabapentin Gabapentin or tramadol Tramadol).
  • And: Bulla osteotomy Bulla osteotomy with bulla irrigation if evidence of otitis media Otitis media.
  • Ventral bulla osteotomy if marked tissue changes in tympanic bulla, eg granulation tissue or bony proliferation.

Monitoring

Subsequent Management

Monitoring

  • Neurological re-examination.

Outcomes

Prognosis

  • Reasonable.

Expected Response to Treatment

  • Neurological signs resolve over a long time period (months) if effective treatment given.
  • Head tilt may be permanent.

Reasons for Treatment Failure

Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Harrison E, Grapes N J, Volk H A & De Decker S (2021) Clinical reasoning in canine vestibular syndrome: Which presenting factors are important? Vet Rec 188 (6), 1-10 PubMed. 
  • Garosi L S et al (2001) Results of magnetic resonance imaging in dogs with vestibular disorders - 85 cases (1996-1999). JAVMA 218 (3), 385-391 PubMed.
  • Dvir E et al (2000) Magnetic resonance imaging of otitis media in a dog. Vet Radiol 41 (1), 46-49 PubMed.

Other sources of information

  • Rosychuk R A W et al (2000) Diseases of the ear. In: Textbook of Veterinary Internal Medicine. 5th edn. Eds: S J Ettinger & E C Feldman. W B Saunders, USA. pp 986-1002.

Other Sources of Information