Introduction

• Inflammation of the external ear canal .
• Affects 4-20% dogs.
• Causes: numerous, categorized into predisposing factors, primary and secondary causes and perpetuating factors.
• Signs: pruritus (usually earliest sign) shown by scratching or head shaking, aural discharge, malodor, and pain - shown by head tilt or dislike of handling of ear.
• Diagnosis:clinical signs, examination and cytology.
• Treatment: topical therapy (ear cleaner and ear drops), systemic therapy, surgery (where chronic irreversible change is present).
• Prognosis: Good if acute, in chronic disease primary causes must be identified and controlled to prevent recurrence. Where chronic change is present (perpetuating factors) this must be treated to prevent recurrence.
  Print off the owner factsheet on Chronic otitis Chronic otitis to give to your client.Follow the diagnostic tree for Evaluating and Managing Otitis Externa/Media Evaluating and Managing Otitis Externa/Media.

Pathogenesis

Etiology

• The PSPP (Primary, Secondary, Predisposing and Perpetuating) model categorizes causes and factors involved with otitis externa into:
  • Primary causes which are diseases that can affect a normal ear canal.
  • Secondary causes which are infections only affecting an ear canal due to inflammation caused by primary causes.
  • Perpetuating factors are usually chronic changes to the anatomy and physiology of the ear canal as a consequence of disease. Unless managed and where possible resolved, otitis will fail to respond to therapy.
  • Predisposing factors are usually breed associated conformational problems of the ear canal anatomy that pre-exist otitis externa and increase the chance of it occurring, eg pendulous ear pinna. They do not cause disease in their own right.
• Primary causes:
  • Allergy - atopic dermatitis Skin: atopy, cutaneous adverse food reaction Skin: food hypersensitivity, contact allergy Skin: allergic contact dermatitis, Otodectes cynotis Otodectes cynotis. Hypersensitivity reactions to other ectoparasites generally affect the ear pinna (Sarcoptes scabiei Sarcoptes scabiei, flea bite  Skin: external parasite bite reaction Skin: flea bite hypersensitivity.
  • Autoimmune diseases - pemphigus foliaceus Skin: pemphigus foliaceus, erythema multiforme Skin: erythema multiforme. Other immune-mediated diseases affect the ear pinna, eg vasculitis Cutaneous vasculitis.
  • Endocrine disorders - hyperadrenocorticism Hyperadrenocorticism, hypothyroidism Hypothyroidism, sex hormone abnormalities Skin: alopecia X.
  • Foreign bodies, especially grass awns .
  • Fungal infections - dermatophytosis Skin: dermatophytosis, aspergillosis Aspergillosis: disseminated.
  • Parasites Ear: parasitic otitis - Neotrombicula autumnalis Skin: neotrombicula autumnalis infestation, Demodex spp Skin: demodectic mange, Otodectes cynotis, Sarcoptes scabiei Skin: sarcoptic mange, tick spp.
  • Others - sebaceous gland hyperplasia Sebaceous gland; hyperplasia neoplasia, sebaceous gland hypoplasia, lipid-responsive seborrhea, primary idiopathic seborrhea Skin: primary seborrhea, granulomatous sebaceous adenitis Skin: idiopathic granulomatous sebaceous adenitis, vitamin-A responsive dermatosis Skin: vitamin A -responsive dermatosis, zinc-responsive dermatosis, idiopathic inflammatory/hyperplastic otitis of cocker spaniels, juvenile cellulitis Juvenile cellulitis and distemper Canine distemper disease.
• Secondary causes:
  • Bacteria.
  • Acute disease predominantly Gram positive organisms especially Staphylococcus spp Staphylococcus spp, Streptococcus spp Streptococcus spp and Enterococcus spp.
  • Chronic disease switch to a more Gram negative infection especially Pseudomonas spp Pseudomonas, E. coli Escherichia coli, Proteus spp Proteus spp.
  • Yeast - Malassezia Skin: malassezia disease Malassezia pachydermatis and Candida spp Candida albicans (uncommon cause of otitis).
• Perpetuating factors:
  • Chronic changes within the ear canal - inadequate epithelial migration (self-cleaning of ear canal), hyperplasia/fibrosis/calcification of ear canal wall, glandular hyperplasia (apocrine or sebaceous gland).
  • Tympanic abnormality - dilation or rupture, choleasteatoma.
  • Chronic change within the tympanic bulla - otitis media Otitis media.
• Predisposing factors:
  • Conformation - excessive hair, pendulous pinna, narrow canal.
  • Moisture in ear canal - swimming, bathing, humid climate.
  • Ear canal obstruction - polyp, neoplasia (can also be primary cause) .
  • Primary otitis media.
  • Systemic catabolic state.
  • Unnecessary overtreatment or reaction to topical treatment, eg irritation from prolonged use of topical medications, water based products, acids, proplyene glycol, alcohol.
  • Physical damage from cleaning - physical or chemical damage.

Diagnosis

Treatment

Outcomes