15 Dec 2014
Filippo De Bellis
Job Title
Part one of this article will cover pathogenesis and clinical signs of otitis externa and media, while part two will look at principles of ear cleaning, ear flushing and myringotomy, along with medical therapy, including topical and systemic medications and ototoxicity.
The clinical signs of otitis externa are a response to underlying problems; many different factors can cause or exacerbate otitis. Recognition and correction is the key to successful management.
Usually the underlying problems are divided into:
• Predisposing factors, which contribute to the development of the condition by altering the anatomy and physiology of the ear canal. These are usually breed-related and include stenotic ear canals (Shar Peis, English bulldogs), excessive hair in ear canals (poodles), and long, pendulous ear pinnae (basset hounds, bloodhounds). Other problems include climatic factors, such as frequent swimming with a secondary increase in humidity in the ear or iatrogenic (over-cleaning, frequent depilation) with subsequent maceration and inflammation.
• Primary factors, which include parasites, foreign bodies, obstructions (inflammatory polyps or tumours) and allergies. Other primary factors include autoimmune-diseases, keratinisation defects and glandular tissue defects (for example, spaniels have increased density of ceruminous and sebaceous glands).
• Secondary factors, which increase the severity of the ear problem and play a major role in chronic or recurrent otitis externa. They include bacterial and fungal infections.
• Perpetuating factors, which are responsible for relapses and increase the difficulties in managing the otitis. They arise as a result of changes in the otic environment and secondary pathologic changes. The most common include otitis media, often a source of constant reinfection of the outer ear, acting as a reservoir for microbes and pro-inflammatory toxins, tympanic membranes alterations (invaginations can trap debris and bacteria leading to chronic otitis media) and progressive pathologic changes (oedema, fibrosis, glandular hyperplasia).
The normal ear canal should have a thin, smooth and pale pink appearance. The most common pathological findings include:
• Swollen, moist, erythematous lining of the ear canals suggestive of acute inflammation.
• Firm, fibrous, indurated appearance suggestive of chronic changes.
• Erythema confined to the vertical portion of the ear canal without exudate, suggestive of allergic otitis.
• Erosions and ulcers accompanied by purulent exudate, suggestive of infections caused most likely by Gram-negative bacteria.
• “Cobblestone” appearance to the lining of the ear canals, suggestive of sebaceous and ceruminous hyperplasia.
• Foreign bodies, tumours and parasites.
In general, the most common presentations can be clinically divided into:
• Erythroceruminous otitis. This is the most common, with a degree of inflammation, discharge and chronic changes variable between very mild to severe, rarely presenting with ulcers and most commonly characterised by staphylococcal and/or Malassezia infections. Exudate varies from yellow to dark-brown (Figure 1).
• Suppurative otitis. This is less common and typically characterised by otic pain, ulcerations and purulent discharge, which can vary from yellow to greenish and malodorous (Figure 2). This form is most commonly associated with Gram-negative bacterial infections.
In dogs and cats, otitis media can be primary or secondary. In cats, primary otitis media occurs as a result of an infection ascending through the Eustachian tube to the middle ear. An exact mechanism for the development of otitis media has not been reported, although the bacterial isolates from the bullae of cats with middle ear disease are consistent with respiratory pathogens.
It has been hypothesised that chronic viral upper respiratory infection early in life may play a role in initiating otitis media in cats. In dogs, primary otitis media can also originate from ascending nasal or respiratory infections through the auditory tube, although otitis media most often occurs as an extension of otitis externa. Additionally, it can occur as primary disease due to middle ear or auditory tube abnormalities such as with primary secretory otitis media, most often seen in cavalier King Charles spaniels. It has been speculated the primary otitis in these cases could occur secondarily to structural changes in the soft palate or nasopharyngeal apertures.
Secondary otitis media in cats is reported as a consequence of ear mite infestation with subsequent rupture of the tympanic membrane or as extension of a nasopharyngeal polyp (Figure 3) originating from the middle ear mucosa and growing through the tympanic membrane. Secondary otitis media in dogs can be caused by draining through a damaged ear drum, of exudates, infectious organisms, debris and residuals of medications. Once an inflammatory process is established, a series of pathological changes take place including oedema, ulcerations, granulation tissue formation, and osteomyelitis. Clinical signs of otitis media are variable. Most commonly, dogs and cats with a perforated ear drum show large amount of liquid discharge within the ear canal, often with mucous material produced by the lining of the tympanic bulla. Additionally, due to the close proximity of the inner ear structures, patients with otitis media can also develop vestibular signs.
Summarising, clinical presentation of otitis media can include:
• facial nerve paralysis (Figure 4);
• Horner’s syndrome (Figure 5);
• hearing abnormalities;
• ataxia;
• head tilt (Figure 6);
• ventro-lateral strabismus;
• nystagmus;
• respiratory signs;
• pain on palpation of the base of the ear; and
• reluctance to open the mouth.
Figure 1. Erythema of the concave aspect of the ear pinna and dark-brown ceruminous discharge in a Labrador retriever with Malassezia otitis externa.
Figure 2. Greenish purulent discharge accompanied with crusting, erythema and punctuate ulcerations in a cross breed with Pseudomonas aeruginosa otitis externa.
Figure 4. Facial paralysis in a boxer with otitis media/interna.
IMAGE: S Silva.
Figure 5. Horner’s syndrome in a domestic short haired cat showing right eye miosis and prolapsed third eyelid.
IMAGE: S Silva.
Figure 6. Head tilt in a cavalier King Charles spaniel with peripheral vestibular disease.
IMAGE: S Rodenas.
