Professor of Veterinary Dermatology, Ross Bond discusses the assessment of the horizontal ear canal and tympanic bullae in dogs with chronic otitis.
Ear disease tops the list of the most common presentations at first opinion canine practices. It is often multi-factorial in aetiology, and many of the predisposing, primary, secondary and perpetuating factors that drive otitis are not always readily identifiable and corrected.
Severe and chronic signs may then follow, often with pathological processes involving inaccessible parts of the external ear canal, and may extend to the middle ear and its associated neural structures.
An ancient saying in medicine is “look closely at your patient; it will usually tell you what is wrong”. This statement can be adapted for otitis to “look closely at the entire ear, including the deepest portions of the horizontal canal and tympanic membrane (TM), to ensure that all relevant gross pathology is observed”. Relatively intensive measures are sometimes required if this is to be achieved.
Our approach to chronic ear cases typically involves a dermatological assessment, including cytology and culture where indicated, video-otoscopy under general anaesthesia, and advanced imaging (most often CT) to assess the ear canal, tympanic bullae and surrounding structures. This approach enables us to target each component or factor in the case with specific medical measures where possible, although a surgical option may be needed for irreversible pathological changes.
In chronic otitis, conventional otoscopy in the conscious animal may lead to an incomplete visualisation of the ear canal, particularly if the canal is painful, stenosed, ulcerated or filled with cerumen or exudate. Premedication with oral prednisolone at 1 mg/kg SID for two or more weeks is often required to reverse hyperplasia / stenosis, where possible, so that the canal is sufficiently patent to accept the otoscope. Failure to improve stenosis with this regime is a negative prognostic indicator for medical therapy.
The enhanced magnification and illumination provided by a video-otoscope (Fig. 1), when compared with a conventional hand-held device, is invaluable for assessment of deeper structures within the ear canal. Changes can be better characterised, and images captured for client education and review of evolution over time. The working channel allows tools (such as forceps and catheters) to be passed for procedures whilst maintaining real-time visualisation.
Dispersal and flushing of wax or exudate is an essential prerequisite for the examination of the entirety of the canal. We favour a dioctyl sodium sulphosuccinate, carbamide peroxide and propylene glycol-containing product (Otoprof, ICF) which speeds the process of dispersing exudate. Copious lavage using warmed sterile saline limits the possibility for post-flushing irritation. Sterile saline is preferred as tap water may contain pseudomonad or other pathogenic bacteria.
This process should be continued until the ear is clean so that the entire canal can be examined in detail. Targeted flushing using tools introduced via the working channel is often required to remove ceruminoliths and adherent material from the distal horizontal canal.
Deep visualisation allows an assessment of the TM and may reveal the presence of foreign bodies (Figs 2A-B), polyps, neoplasms and cysts (Figs 3A and B). Myringotomy (Fig. 4) can be conducted where indicated by gross TM appearance or CT findings. Taken together, these processes allow for more accurate prognoses, specific therapy, and when required, earliest possible surgical intervention.
There is little doubt that detailed evaluations of the ear structures by combined advanced radiological imaging and video-otoscope technology allows for improved diagnosis and optimised therapeutic regimens - and therefore maximal opportunities for best outcomes in severe and chronic otitis cases. RVC Small Animal Referrals is well placed to deal with these chronic and complex cases whose signs may cross traditional specialty boundaries and thus benefit from input from dermatologists, radiologists, neurologists and soft tissue surgeons under the same roof.
For small animal referrals, please call: 01707 666365