Clinical signs associated with otitis externa, the most common outer ear canal disease in dogs, consist of head shaking, scratching, otic pain (otalgia) and otic discharge (otorrhea). In some cases, aural hematomas (othematoma) can be seen. Causes of otitis externa are numerous, therefore a thorough and complete clinical examination is mandatory for correct diagnosis and therapy. It should include a general physical, dermatologic, neurologic (cranial nerves) and otoscopic examination. For complete visualization of the tympanic membrane and prior to therapy, ear flushing is necessary. However, before flushing, material should be obtained from the horizontal part of the ear canal for cytologic examination, culture and susceptibility testing. After flushing, masses can easily be identified and samples can be taken for histopathology.

Additional examination, like diagnostic imaging (radiography, CT-scan, MRI), is usually not necessary for outer ear diseases except in case of para-aural abscessation, otitis media/interna and neoplasia.

Otitis externa in dogs has numerous causes, usually classified as primary, predisposing or perpetuating factors.^1-4 Primary factors directly cause otitis externa and include parasites (ear mite; Otodectes cynotis), foreign bodies, inflammatory polyps, tumors, hypersensitivities (atopy, food hypersensitivity), endocrine abnormalities (hypothyroidism) and keratinization disorders.^1-4 Predisposing causes of otitis externa make the ear canal more susceptible to inflammation and secondary infection. These factors include anatomical conformation (pendulous ears, narrow ear canals and excessive hair growth) and changes in the external environment of the ear canal (excessive moisture, excessive ear cleaning or trauma from cotton swabs).^1-4 Perpetuating factors exacerbate and maintain the disease even after the primary factors are eliminated and include secondary bacterial and/or yeast infection, otitis media and inappropriate treatment.^1-4

In most cases of chronic otitis externa, primary factors, predisposing and/or perpetuating factors can and should be identified and treated. In chronic cases, elimination of underlying factors however, usually doesn't end the inflammatory process. Management should then be aimed at thoroughly cleaning and drying the ear canal and administering appropriate topical therapy for a longer period of time, sometimes even a life-long treatment is necessary. For treatment purposes, three types of otitis externa can be distinguished; ceruminous to purulent otitis externa (with intact skin and no obvious hyperplasia/proliferation of the skin), ulcerative otitis externa (epithelial lining with ulcerative erosions) and proliferative OE (with significant ear canal narrowing).

A protocolar approach to treatment of chronic otitis externa is recommended based on these three types of OE. Ointments with broad-spectrum antibiotics and corticosteroids should be used with careful attention to complete filling of the entire ear canal in case of ceruminous to purulent and proliferative otitis externa, pending the results of culture and sensitivity testing. In most cases the frequency of treatment can be tapered off based on clinical effect and control otoscopy. In some cases the treatment should be adjusted to the results of control otoscopy and culture and sensitivity testing. In case of ulcerative otitis externa, topical medication should be used not containing any corticosteroids until the ulcerations have healed. A guideline for treatment is provided in the flowcharts. Total ear canal ablation is reserved for unresponsive or proliferative chronic otitis externa.

References

1.  August JR. Otitis externa: a disease of multifactorial etiology. Vet Clin North Am Small Anim Pract 1988;18(4):731–742.

2.  Griffin CE. Otitis externa and otitis media. In: Griffin CE, Kwochka KW, MacDonald JM, editors. Current Veterinary Dermatology: The Science and Art of Therapy. St. Louis: Mosby Year Book; 1993:245–262.

3.  Cole LK, Kwochka KW, Kowalski JJ, et al. Microbial flora and antimicrobial susceptibility patterns of isolated pathogens from the horizontal ear canal and middle ear in dogs with otitis media. J Am Vet Med Assoc 1998;212(4):534–538.

4.  Rosser EJ. Evaluation of the patient with otitis externa. Vet Clin North Am Small Anim Pract 1988;18(4):765–772.