Chronic Otitis Externa Secondary to Tympanic Membrane Electrode Placement in Rhesus Macaques (Macaca mulatta)

Otitis externa (OE) is a condition that involves inflammation of the external ear canal. OE is a commonly reported condition in humans and some veterinary species (for example, dogs, cats), but has not been reported in the literature in macaques. Here, we present a case series of acute and chronic OE likely precipitated by abrasion of the ear canal with a tympanic membrane electrode in 7 adult male rhesus macaques (Macaca mulatta). All animals displayed purulent, mucinous discharge from 1 or both ears with 3 macaques also displaying signs of an upper respiratory tract (URT) infection during the same period. A variety of diagnostic and treatment options were pursued including consultation with an otolaryngologist necessitated by the differences in response to treatment in macaques as compared with other common veterinary species. Due to the nature of the studies in which these macaques were enrolled, standard audiological testing was performed before and after OE, including tympanometry, auditory brainstem responses (ABRs), and distortion product otoacoustic emissions (DPOAEs). After completion of study procedures, relevant tissues were collected for necropsy and histopathology. Impaired hearing was found in all macaques even after apparent resolution of OE signs. Necropsy findings included abnormalities in the tympanic membrane, ossicular chain, and middle ear cavity, suggesting that the hearing impairment was at least partly conductive in nature. We concluded that OE likely resulted from mechanical disruption of the epithelial lining of the ear canal by the ABR electrode, thereby allowing the development of opportunistic infections. OE, while uncommon in macaques, can affect them and should be included as a differential diagnosis of any macaque presenting with otic discharge and/or auricular discomfort.