The Patient with Otitis Externa
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JAN 09, 2007
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Otitis externa may be seen with many diseases in conjunction with other clinical signs, which are helpful in the formulation of a list of differential diagnoses. This discussion is the approach to the dog with otitis externa and no other symptoms.
It is important to differentiate between predisposing, primary, and perpetuating factors in the pathogenesis of otitis externa. Predisposing factors are independent from the underlying disease and alone will not cause disease, but will facilitate the pathologic process. Conformation, including dense hair in the ear canal, a long and narrow ear canal, pendulous ears, and climate-related seasonal factors such as increased temperature and humidity are examples of predisposing factors. Complicating factors occur only after the primary pathologic process has begun, but continue to be a problem after the primary disease has been successfully identified and treated. Examples are otitis media, bacterial or fungal infections, and chronic proliferative changes due to inflammation. These complicating factors need to be treated independently. The most common primary factors are listed in Table 2-12.
Key Questions
> How old was this patient when clinical signs were first recognized?
> Is the disease seasonal?
> Are there any other animals in the household?
> Was the disease treated before? If so, which drugs were used and how successful was treatment?
> When was the last medication given?
Differential Diagnoses, Important Clinical Clues, Recommended Diagnostic Tests, Treatment Options, and Prognosis in a Patient with Otitis Externa | ||||
Disease | Comments | Diagnostic Tests | Treatment | Prognosis |
Atopy* (hypersensitivity to aeroallergens such as pollens, house dust mites, or mold spores) (Fig. 2-65) | In some patients a seasonal condition; unilateral otitis externa may be caused by atopy | Diagnosis based on history, physical examination, and ruling out differential diagnoses. Intradermal skin test or serum test for allergen-specific IgE identify offending allergens and allow formulation of immunotherapy | Allergen-specific immunotherapy, antihistamines, essential fatty acids, glucocorticoids, topical glucocorticoids | Good for well-being of the patient with continued management, guarded for cure |
Otodectes cynotisinfestation (very common cause, particularly in young animals and cats) | Coffee grounds appearance of debris in the ear canals | Otoscopic examination. Microscopic evaluation of debris from ear swabs suspended in mineral oil; miticidal treatment trial | Antiparasitic agents such as ivermectinsystemically, although many patients will respond to topical miticidal therapy | Excellent |
Foreign body | Typically unilateral and of acute onset | Otoscopic examination | Removal | Excellent |
Scabies (a highly contagious disease caused by Sarcoptes scabiei var.canis in dogs and Notoedres cati in cats) | Edges and lateral aspects of pinnae affected as well as (or worse than) the canal (Fig. 2-66) | Superficial skin scrapings, sarcoptes treatment trial | Antiparasitic agents | Excellent |
Food adverse reaction (may or may not be allergic; commonly a reaction against a protein, rarely an additive; clinically indistinguishable from atopy) | Unilateral otitis externa maybe seen with food adverse reactions | Elimination diet | Avoidance, antihistamines, essential fatty acids, glucocorticoids, topical glucocorticoids | Excellent, if offending protein(s) is (are) identified and avoided; otherwise fair with continued management. Poor chance of cure |
Hyperadrenocorticism* (spontaneous or idiopathic. The spontaneous form is an excessive production of glucocorticoids either due to a microadenoma or macroadenoma of the pituitary gland (PDH, 85%) or due to adrenocortical neoplasms in 15%) | Subtle clinical signs may be overlooked (see Table 2-5). Complete response to therapy of secondary ear infection | Serum biochemistry (SAP , cholesterol , ALT , glucose , urea , hemograms (leukocytosis, neutrophilia, lymphopenia and eosinopenia), urinalysis (specific gravity , cortisol:creatinine ratio ), radiographs (hepatomegaly, osteoporosis, mineralization of adrenal glands), low-dose dexamethasone suppression test, ACTH assays, ultrasonography (adrenal gland size ), ACTH stimulation test | Iatrogenic form: discontinue glucocorticoid administration. Idiopathic form: o,p´- DDD (mitotane), ketoconazole for PDH, surgical removal of affected gland for adrenocortical neoplasia | Approximately 60% of dogs with adrenal tumors were reported to survive adrenalectomy and the postoperative period. The average life expectancy was 36 months. Adrenal adenocarcinomas have a better prognosis than adenomas. The life span of dogs with PDH treated medically averaged 30 months with some dogs living longer than 10 years and others only days. |
Pemphigus foliaceus* (immune-mediated skin disease characterized by intraepidermal pustule formation due to pemphigus antibodies against antigens in the intercellular connections. May be drug-induced or paraneoplastic) | Inner surface of pinnae typically worse than canals (Fig. 2-67) | Cytology, biopsy | Immunosuppression | Fair with appropriate treatment, poor for cure (except drug-induced pemphigus) |
Neoplasia* (ceruminous gland adenomas and adenocarcinomas-both types in cats, the former more common in dogs) | Unilateral, older animals | Otoscopic examination | Surgical excision (vertical or complete ablation of the ear canal) | Good, if completely excised and no metastases |
Hypothyroidism (lymphocytic thyroiditis, presumably autoimmune, or idiopathic thyroid necrosis which may be end-stage lymphocytic thyroiditis) | Subtle other clinical signs may be overlooked (see Table 2-5). Complete response to therapy of secondary ear infection | Serum biochemistry (SAP , cholesterol , ALT ), hemograms (anemia), thyroid tests (free T4, total T4, free T4 by equilibrium dialysis, TSH assays, TSH stimulation test, TRH stimulation test) | Hormone replacement therapy with levothyroxine | Good, although not all patients stay in complete and constant remission despite adequate supplementation. |
Idiopathic seborrhea* (primary keratinization defect as autosomal recessive trait with decreased epidermal cell renewal time and thus hyperproliferation of epidermis, sebaceous glands, and follicular infundibulum secondary to inflammation, endocrine disease, or nutritional deficiencies). | Excessive wax formation even with topical medication. | Biopsy | Ear cleaners, retinoids, corticosteroids | Fair to guarded for well-being; poor for cure |
Figure 2-65. Pinnal erythema, scaling, and erosions in a West Highland White Terrier with atopy (Courtesy of Dr. Sonya Bettenay).
Figure 2-66. Pinnal scaling and crusting in a male Great Dane with scabies (Courtesy of Dr. Sonya Bettenay).
Figure 2-67. Pinnal otitis in a 2-year-old, male Whippet with pemphigus foliaceus (Courtesy of Dr. Sonya Bettenay).
Cytology is essential in any dog or cat with otitis externa; examination must be separate in the left and right ear canals as infective microorganisms may be different from one ear to the other. In some animals, particularly in patients with chronic long-standing otitis externa and concurrent otitis media, organisms in the middle ear may differ from those isolated in the external ear. Antimicrobial treatment in the ear canal is most effective topically and determined by cytology and in vitro susceptibility. Repeat cytology examinations during treatment are essential and changes in the otic flora may necessitate changing medications.
Otitis media is best treated with systemic medication. Many dogs with chronic otitis externa and otitis media may not respond to treatment because of severe accumulation of purulent or waxy material in the ear canals. An ear flush under anesthesia may be needed followed by a new attempt of topical and concurrent systemic therapy. The tympanum may rupture prior to flushing or during flushing because in an inflamed ear the tympanum is much more fragile than normal. Frequently there are few alternatives for antimicrobial treatment in these patients. Sometimes they may have to receive potentially ototoxic topical medication. Be sure to discuss this possibility with owners before beginning therapy. Regular cytologic examinations are a precondition for successful management of patients with otitis externa. They are not specifically mentioned in Fig. 2-68. Therapeutic trials and tests for primary diseases may be influenced by concurrent topical medication and thus must be planned, executed, and interpreted with care. Chronic long-standing otitis externa is extremely frustrating for patients, clients and veterinarians, and patients may benefit from referral to a veterinary dermatologist.
Figure 2-68. Identification of the primary disease in the patient with otitis externa.
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How to reference this publication (Harvard system)?
(2007) “The Patient with Otitis Externa”, Dermatology for the Small Animal Practitioner. Available at: https://www.ivis.org/library/dermatology-for-small-animal-practitioner/patient-otitis-externa (Accessed: 23 March 2023).
Affiliation of the authors at the time of publication
Department of Clinical Sciences Coll. of Veterinary Medicine & Biomedical Sciences, Colorado State University, Fort Collins, CO, USA.
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