Otitis externa is a common condition observed in everyday clinical practice.

It is usually straightforward, but successful management must involve identifying and managing the underlying cause. Causes should be classified as either predisposing, primary, or perpetuating. Recognition of these factors is critical to long term control of chronic otitis.

Predisposing Factors

The external ear canal is defined as the pinna, horizontal and vertical canals, and the tympanic membrane. Factors that directly change the microenvironment of the ear canal are predisposing factors. They facilitate inflammation by permitting the external ear canal microenvironment to be altered, which allows pathogenic or opportunistic bacteria to become established. These factors include:• Conformation of the ear canal- Pinnae (floppy vs erect ears): Evidence suggests there is a higher prevalence of otitis externa in floppy ears.- Length and conformation of ear canals- Stenosis or swelling of the opening of the external ear canal: Lack of a significant opening into the canal allows otic secretions to accumulate, providing a medium for growth of pathogenic bacteria, and may also reduce air circulation. This is a notable problem in some breeds, such as shar-peis.• Environmental factors: Heat and humidity tend to create a microenvironment that is suitable for bacterial and yeast growth. Dogs that swim may be predisposed to otitis due to excessive moisture and humidity.• Improper treatment: Trauma to the ear canal during treatment can damage the epithelial lining and predispose the canal to infections.

It is important to note that predisposing factors alone do not cause otitis; they need to be paired with another factor to cause disease. For example, a dog with floppy ears and underlying atopy is predisposed to otitis because it is easier for pathogen flora to become established.