Diagnostic otology (Proceedings)
Non-responsive or chronic and recurrent otitis externa is a common reason for pet owners to leave their regular veterinarian and seek second (and third, fourth and fifth........) opinions. Proper management of these conditions takes a co-ordinated approach that includes strong history taking skills (keeping in mind the primary, predisposing and perpetuating factors involved in otitis), a thorough physical and otoscopic evaluation, appropriate diagnostic tests and the institution of a sound therapeutic plan that addresses the underlying factors while treating the current condition. The problem is that all we have to work with is a little tube on the side of the head!!
Factors related to otitis externa
Primary factorsPrimary factors are direct causes of the otitis. They produce inflammation of the ear canal epithelium, and the resultant clinical signs of disease. Examples of primary factors include otodectic otitis, hypersensitivity (including contact allergy), disorders of cornification (e.g. primary seborrhea, sebaceous adenitis), endocrinopathies (e.g. hypothyroidism), immune disorders (e.g. pemphigus), and foreign bodies such as hair or grass awns (or even cotton swabs!).
Predisposing factors are those that place the animal at risk for developing disease. Examples of predisposing factors include conformation (pendulous pinnae, stenotic canals), excessive moisture in the ear leading to maceration of tissue (swimming, humidity), obstructive disease (tumours, polyps), systemic disease (pyrexia or other debilitating disease leading to immunosuppression) or inappropriate treatment (use of cotton tipped swabs to clean ears, inappropriate use or choice of topical cleaners, vigorous plucking of hairs from ear canal).
Once the primary causes and predisposing factors work together to change the microenvironment of the ear canal, the perpetuating factors act to prevent rapid resolution of the condition. Examples include bacteria (especially Staphylococcus pseudintermedius and Pseudomonas spp.), yeast (e.g. Malassezia pachydermatis), otitis media (a large percentage of dogs with chronic or recurrent otitis externa have had or have a ruptured tympanic membrane), and progressive pathological changes such as fibrosis, calcification, glandular hypertrophy or hyperplasia and so forth.