Ear no evil: Managing feline otitis

Ivonne Wierink/stock.adobe.comOtitis externa and media are not “go-to” diagnoses among feline maladies. In fact, according to Douglas DeBoer, DVM, DACVD, professor of dermatology at the University of Wisconsin School of Veterinary Medicine, aside from ear mites (Otodectes cynotis), otic pathology is rarely blamed for clinical signs of disease in cats. As he explained at the 2019 Atlantic Coast Veterinary Conference, however, feline otitis can fester subtly and be difficult to manage.

Cat ears: not small dog ears

Otitis is diagnosed less commonly in cats than in dogs, Dr. DeBoer said; it's the reason for about 5% of feline veterinary visits versus 15% of canine visits. But when it occurs, it brings idiosyncrasies.

First, anatomic differences exist between the feline and canine middle ear. In dogs, the tympanic cavity-the air-filled chamber of the middle ear-is a single compartment containing an incomplete septum. In cats, this septum is almost complete and divides the cavity into two distinct compartments; this “wall” can impede drainage and lead to occlusion.

Second, the aural microbiome differs between cats and dogs. While Staphylococcus pseudintermedius and Malassezia pachydermatis compose 85% of otitis cases diagnosed in dogs, that's not the case for cats. In one study of stray cats, feline otitis cytology revealed Staphylococcus in 72% of cases, Otodectes in 53%, Malassezia in 51% and rods in 29%.¹

External is not eternal

The presence of foreign bodies and polyps should be ruled out with otoscopy, followed by thorough ear cleaning to remove ceruminous debris. Dr. DeBoer urged caution in ear flushing when the tympanic membrane is ruptured. Chlorhexidine, he said, should never be used in these cases because it can be ototoxic.

Feline otitis is typically managed well with aminoglycoside/steroid combinations, such as Tresaderm (Merial) or Mometamax (Merck Animal Health). Although not approved for cats, florfenicol formulations (Claro-Bayer Animal Health, Osurnia-Elanco) can also be effective, Dr. DeBoer said. He uses these single-dose applications off-label for feline otitis cases for which cytology indicates cocci and treatment compliance is questionable.

When otitis is recurrent, it is typically associated with poor owner compliance, the presence of antimicrobial-resistant organisms, allergy/atopy, ear canal stenosis/occlusion (i.e. polyp) or otitis media.

The middle ground: otitis media

The pathogenesis of middle ear infections-otitis media-differs between dogs and cats. In dogs, it generally results from “descending” bacteria associated with otitis externa. While this route can also occur in cats, feline middle ear infections are more often secondary to “ascending” inflammatory/infectious disease of the Eustachian tube and nasopharynx. These include common upper respiratory infections, such as feline herpesvirus and calicivirus.

“[Feline otitis media] happens a lot more than we realize,” said Dr. DeBoer, “and may occasionally explain some of the bizarre clinical signs we see in cats.”

Clinical signs may include clumsy behavior, head shaking, pawing at the ears, crying when opening the mouth, changes in eating habits, hearing loss and depression. Overt neurologic signs can also present, such as Horner's syndrome, head tilt, nystagmus, ataxia and obtundation.

Feline otitis media may be unilateral or bilateral, and is sometimes secondary to recurrent otitis externa.

Studies show…

In one retrospective review of skull computed tomography (CT) studies performed on 310 cats, evidence of middle ear disease was found in 101 patients. Of those affected, only 26 cats had been imaged due to a complaint suggesting middle ear disease.² The otitis media was an incidental neurologic workup finding in 41 of the cats, and 34 had been imaged for chronic rhinitis. These findings indicate that many cats without a complaint of ear disease have radiographic evidence of middle ear disease.

Another study reviewed 50 feline necropsies. Of 100 ears, 48 had evidence of ongoing or previous otitis media; histologic findings were more common than gross lesions.³

The workup for otitis media should begin with ear swab cytology. Imaging under anesthesia and culture are recommended for recurrent cases. Myringotomy is done to facilitate culture (ideally from the tympanic bulla) followed by middle ear irrigation. Topical and systemic antimicrobials and supportive care are then instituted.

When medical management fails, surgery by ventral bulla osteotomy or, less commonly and particularly indicated with neoplasia, total ear canal ablation may be necessary.

But, Dr. DeBoer, emphasized, “Medical management can work. You don't have to immediately send these guys to surgery.”

References

1. Perego R, Proverbio D, Bagnagatti De Giorgi G, et al. Prevalence of otitis externa in stray cats in northern Italy. J Feline Med Surg 2014;16(6):483-490.

2. Shanaman M, Seiler G, Holt D. Prevalence of clinical and subclinical middle ear disease in cats undergoing computed tomographic scans of the head. Vet Radiol Ultrasound 2012;53(1):76-79.

3. Sula MM, Njaa BL, Payton ME. Histologic characterization of the cat middle ear: in sickness and in health. Vet Pathol 2014;51(5):951-967.

Dr. Capuzzi, who earned her BS and VMD degrees from the University of Pennsylvania, works in small animal practice in the Philadelphia area and is a published author. She has written for The Philadelphia Inquirer, Time, Business Philadelphia, Dog Fancy and Dog World, among others. She is especially interested in public health and animal welfare, and is involved with several organizations whose missions are to improve the lives of domesticated and wild animals.