Image Quiz: A chronically ear-scratching, head-shaking golden retriever (Sponsored by Dechra)

Sammy, a 4-year-old 70-lb (31.8-kg) neutered golden retriever, was presented in early autumn with the chief complaint that he had been scratching his ears and shaking his head during the past four to five weeks. The owner reported that this happens every summer. When this occurs, the owner administers eardrops left over from a previous prescription. The drops contain thiabendazole, dexamethasone, and neomycin. In contrast to previous episodes, the dog's clinical signs continued this time despite administration of the eardrops.

Upon physical examination of the dog, abnormal findings were limited to his ears. The pinnae and vertical canals were normal. The ears had a moderate amount of creamy exudate lining the horizontal canals. There was moderate erythema with mild cobblestone hyperplasia involving the proximal vertical canal and the entire horizontal canal in both ears (see below).

The tympanic membrane was visible, intact, and normal in both ears. Cytology samples were collected from both ears (see below).

Which would be the least appropriate treatment to use in this case of otitis externa?

a) A topical fluoroquinolone/steroid-containing medication

b) A topical polymyxin/steroid-containing medication

c) A topical gentamycin/steroid-containing medication

d) Tris-EDTA