Otitis Externa, a common clinical problem in dogs (less frequent in cats), is often a frustrating disease to cure or even control.  

Primary and predisposing causes of Otitis Externa

• Parasites
• Allergy
• Contact irritant
• Keratinization disorders (epidermal maturation problems and Sebaceous Adenitis)
• Autoimmune diseases or disorders
• Foreign body
• Metabolic diseases or disorders
• Conformational abnormalities (which can alter the microenvironment)
• Microanatomy variability among species (Cocker Spaniel, Labrador Retriever, Spaniels have been found to have more apocrine glands and hair follicles than mongrel dogs)
• Excessive moisture (medications, swimming, etc. can macerate the tissue)
• Obstructive ear disease can trap moisture and debris
• Overzealous cleaning

Secondary invaders

• Yeast (Malassezia pachydermatis)
• Gram positive bacteria (ie. Staphylococcus sp.)
• Gram negative bacteria (ie. Pseudomonas, Proteus spp, etc.)

 Contributing factors to chronicity of lesions

• Chronic inflammation causes the epithelial lining of the ear canal to be thrown into proliferative folds which can hinder cleansing
• Chronic inflammation stimulates epidermal thickening, enlarged ceruminous glands and fibrosis (scar) which may lead to a stenotic (narrowed) canal
• Chronic inflammation reverses the body’s natural debris removal process and may actually allow for debris to accumulate in the deeper regions of the canal
• Scar tissue and calcification may result from chronic inflammation - may cause excessive discomfort and trap infection
  
  

Treatment

A combination of routine use of ear cleansers and application of topical medication. The cleanser and medication used depends the diagnosis and confounding factors. For example, the pH of the cleanser is important in determining selection since some microorganisms respond faster to an acid or basic pH.

Contributed by:  Karen Helton-Rhodes, DVM, Diplomate ACVD

Illustration reprinted with permission by the copyright owner, Hill’s Pet Nutrition, Inc.