What is otitis externa?
Otitis externa is an inflammation of the external ear canal distal to the tympanic membrane (ear drum), with or without the involvement of the ear pinna (ear lobe). It is one of the most common reasons that dogs and cats are taken to the veterinarian. Otitis externa can be acute or chronic, unilateral or bilateral.
Some of the primary causes are parasites (e.g., Otodectes species), allergic disorders (e.g., atopy, food hypersensitivity), foreign bodies, immune-mediated disorders, seborrhea, or endocrinopathies (e.g., hypothyroidism).
Risk factors include ear anatomy (e.g., pendulous pinna, canal stenosis), environmental humidity and heat, swimming or bathing, excessive ear cleaning, and systemic disorders with immune compromise. Bacteria, yeast, and other fungal infections, as well as proliferative changes and treatment errors or reactions, all contribute to otitis persistence.
What are the clinical signs of otitis externa?
Otitis externa is classified according to its causes and factors. The causes are various diseases/infectious agents that cause otitis and can be either primary or secondary. Factors that alter the structure, function, or physiology of the ear canal also contribute to or promote otitis externa. Predisposing factors exist prior to the development of ear disease, whereas perpetuating factors occur as a result of the disease. Predisposing factors are primarily breed/species-specific, with pendulous ear pinnae as a recognized t predisposing factor in breeds like Spaniels and Basset hounds. Other breeds include English Cocker Spaniel, Brittany spaniels, Labrador and Golden retrievers, West Highland White Terrier, Scottish Terrier, Fox Terrier, Maltese terriers and German Shepherd dogs.
Breed predispositions for primary factors are important in cases like allergies (atopic dermatitis) and cutaneous adverse food reactions plus Idiopathic inflammatory/hyperplastic otitis of cocker spaniels.
Some of the breeds predisposed to otitis externa
Although all factors and causes must be addressed in the end, primary causes in particular must be managed to reduce the continuation or recurrence of otitis.
The clinical signs include pain in the affected ear, pruritus with headshaking or scratching the affected ear, erythema (reddening), swelling, scaling, or crusting of the pinna and/or external canal, and odiferous otic discharge. Aural hematomas develop when there is constant shaking of the head due to ear infections.
An aural hematoma is a blood-filled subcutaneous fluctuant swelling on the ear pinna formed when traumatic rupture of the capillaries and separation of the auricular cartilage and skin occurs. In some instances, acute moist dermatitis of the face develops too. Other more generalized dermatological signs applicable to the primary cause of the otitis, eg allergy - pruritus elsewhere on the skin (pedal saliva staining); and in epithelialization disorders - generalized seborrhea.
How is otitis externa diagnosed?
Otitis externa is an inflammation of the ear canal and requires identification of the underlying cause for successful treatment. Cytologic examination, including ear swabs and fine-needle biopsy, is important for accurate diagnosis and monitoring response to therapy. Discharge is collected using a cotton swab before cleaning the ear canals, and is then evaluated for mites and other organisms under a microscope. The number and type of bacteria, yeast or fungal organisms, inflammatory cells, cerumen, and neoplastic cells are also assessed.
How is otitis externa treated?
Owner compliance, inflammation management, directed antimicrobial therapy, and workup of the underlying cause are all required for the successful treatment of otitis externa. Owners must have realistic expectations and recognize that resolving or improving otitis externa may take time. The underlying causes of otitis externa must be managed and antimicrobials are chosen based on history and cytology.