57 Otitis externa and otitis media in a dog
Otitis externa is a common clinical presentation. It is often of multifactorial aetiology and may be part of a generalized skin disease or underlying systemic illness. Although initial symptomatic therapy is appropriate for early, acute cases of otitis externa, a systematic and thorough approach involving detailed history taking, complete physical and dermatological examinations, and appropriate diagnostic work-up is required when investigating and treating chronic otitis externa. This case report describes the investigation and treatment of a case of Pseudomonas otitis externa.
A detailed history is of paramount importance in understanding the nature of the underlying causes of long-standing otitis externa. It is important to establish the age of onset, seasonality, whether there is evidence of more generalized skin disease or pruritus, and whether there are symptoms of systemic disease. Additional important information is whether the otitis has been unilateral or bilateral, is there aural pruritus or pain, the nature of the aural discharge and whether there are symptoms suggestive of otitis media, such as pain on opening the mouth or neurological signs. Lastly, it is useful to know details of previous treatment and response.
If the ears are painful, general anaesthesia is required to clean and facilitate examination of the ear canals and tympanic membranes. Bulla radiography can be helpful in evaluation of chronic otitis externa and is an aid in deciding whether the ear problem can be managed medically or whether surgery is indicated. The full bulla series consists of ventrodorsal, open-mouth rostrocaudal, lateral, and left and right oblique views. In practice, the first two views usually prove to be the most useful. External ear disease may manifest as calcification of the auricular cartilages and narrowing of the external ear canals. Changes consistent with otitis media include increased density of the air-filled bullae, thickening, lysis or irregularity of the wall of one or both bullae, changes in size and contour, and new bone production. Note that in at least a quarter of cases of otitis media these changes are not present.
A diet trial, intradermal testing and blood work were indicated in this case and, as treatment of the otitis was likely to require glucocorticoid therapy, the decision was made to do intradermal testing at this stage.
There was evidence of Pseudomonas otitis externa and media. There was also evidence of pyoderma and Malassezia dermatitis. It was likely that both the skin and ear disease were secondary to an underlying hypersensitivity disorder.
In this case, the ear canals were not irreversibly diseased and it was considered that medical management of the otitis was appropriate. Treatment would require resolution of the bacterial otitis, and identification and management of the underlying allergic disease. The owner was advised that, even with successful resolution of the infection, the patient was likely to require lifelong management of the underlying allergy and was also likely to require lifelong regular ear cleaning. Furthermore, even following apparently successful therapy, Pseudomonas otitis may recur in around 20% of cases.