Ear cytology in otitis externa: when, why, how?
Abstract
Otitis externa is a common presentation in small animal practice. Due to the increasing concerns regarding antibacterial resistance both in human and veterinary medicine, empirical therapy of otitis externa with antibiotics-containing topical products without a specific diagnosis should be avoided. This article reviews how to perform cytological examination of ear discharge, and how it can be used to characterise infection and target therapy in order to optimise the management of the disease.
Otitis extema is an acute or chronic inflammation of the external ear canal. It is a common clinical finding, with a prevalence of about 10 to 20% in dogs and 2 to 6% in cats (Angus, 2004; Saridomichelakis et al, 2007). A number of factors may be involved in its development, and primary causes, predisposing factors and perpetuating factors need to be considered. Primary causes are those that can directly induce inflammation and cause disease in a normal ear (Table 1). Predisposing factors by themselves will not cause otitis externa, but increase the likelihood of an inflammation developing by altering the normal structure or environment in the ear canal (Table 2). Perpetuating factors such as secondary infections develop as a consequence of inflammation and maintain inflammation even if the primary factor has resolved (Table 3).
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