Preventing Recurrence of Otitis Externa

In the Literature

Léonard C, Taminiau B, Ngo J, Fantini O, Daube G, Fontaine J. Preventive use of a topical anti-inflammatory glucocorticoid in atopic dogs without clinical sign of otitis does not affect ear canal microbiota and mycobiota. Vet Dermatol. 2021;32(4):355-e98.

The Research …

Atopic dermatitis is the most common cause of otitis externa in dogs, and the skin and ear canals of atopic dogs are less biodiverse than those of healthy dogs.¹ Regular application of topical steroids can help prevent flares of otitis externa, but the effects on microbiota and mycobiota of the ear canal are unknown. 

This study evaluated 10 atopic dogs without currently active otitis externa. Mometasone (0.3 mg) was applied to the right ear canal of each dog twice weekly for 4 weeks; left ears served as controls. Dogs were evaluated weekly, and clinical and cytologic evaluations of the external ear canal were performed at each visit. 

Samples were obtained from each ear for DNA  sequencing at the start of the study and again on days 14 and 28. No changes in bacterial or fungal diversity were noted between treated and untreated groups over time. No changes in clinical or cytologic indexes were noted in the control ears between days 0 and 28; however, by day 28, a significant difference was noted in the treated ears, which had no cytologic evidence of microbes. 

The most common isolated bacterial families were Staphylococcaceae, Corynebacteriaceae, Moraxellaceae, and Flavobacteriaceae. The most commonly isolated genera of fungi were Malassezia spp and Cladosporium spp.

… The Takeaways

Key pearls to put into practice:

• Topical steroids are essential for preventing recurrent otitis externa. Study results showed no cytologic evidence of microbes in treated ears. This finding is important because it was achieved solely through application of steroids, without use of antimicrobial products.

• Lack of cutaneous microbial diversity is a feature of canine atopic dermatitis. During the 4- week study, microbial diversity did not change. It is unknown whether this would remain true over a longer period. Further studies are needed to determine whether long-term application  of topical steroids can normalize the microbial populations of the ear canal.

• Topical steroids can have systemic effects in dogs. Mometasone ear medications have been shown to not affect intradermal allergy testing,² but a study evaluating auricular dexamethasone  application found mild changes in adrenal gland function.³ Further studies are needed to determine the effects of regular topical steroid application on adrenal function.