Otitis in cats: causes, diagnosis and treatment
Otitis in cats should be considered a multifactorial problem that requires a specific approach distinct from that used in dogs.
Introduction
By definition, the term otitis refers to inflammation of the inner ear and/or pinna. Generally speaking, when referring to otitis in cats without specifying anything else, we are talking about otitis externa, a comprised external auditory canal and/or pinna, without affecting the eardrum; in the case of otitis media or interna, however, the location is usually specified.1,2
Compared with its prevalence in dogs, otitis in cats is a relatively uncommon disorder.3 Perhaps that is why there are only a few studies on the subject, particularly any looking at large populations. The few studies that have assessed the prevalence of otitis in cats have produced varied results, with values ranging from 2–19% in cats with an owner.4 In contrast to this data, a study of stray cats in Italy reported a prevalence of otitis externa of 55%.5 However, a Belgian study of stray cats concluded that the vast majority of animals examined had healthy ears.2
Otitis in cats: clinical characteristics and causes
Most owners who bring in a cat with suspected otitis report that it shakes its head, scratches and shows signs of pain of variable intensity when its ears are touched, together with an excessive production of earwax and/or a bad odour.
The physical examination usually reveals excoriations, erythema, scabs and oedema of the auditory canal and/or pinna. Their is also the possibility of otohaematoma secondary to scratching.4
The correct management of otitis in cats should start by identifying the primary cause, that is, the actual reason for the inflammation, and assessing any predisposing factors (which increase the risk of developing otitis, but do not cause it) or perpetuating factors (which do not cause the initial inflammation, but are responsible for some clinical signs and hamper recovery).4
Otitis in cats: primary causes
Primary causes of otitis in cats include parasites (Otodectes cynotis, Demodex cati), fungi (dermatophytes, Aspergillus spp., Sporothrix schenckii and Cryptococcus neoformans), allergic diseases (atopy, food allergy), keratinisation disorders (idiopathic ceruminous otitis, idiopathic facial dermatitis in Persian and Himalayan cats, primary hypothyroidism, sebaceous glands disorders), and immune-mediated diseases (proliferative necrotising otitis externa, pemphigus foliaceus).4
O. cynotis is the most relevant primary cause as it is responsible for some 53–69% of cases. It mainly affects young cats and usually courses with bilateral pruritus and a dark brown ceruminous exudate reminiscent of ground coffee. It can coexist with secondary Malassezia spp. infections and O. cynotis is isolated outside the auditory canal in up to 23% of cases.1,4
Otitis in cats: predisposing factors
Some of the main predisposing factors for the onset of otitis are ear cleaning when not strictly necessary and obstruction of the auditory canal, which may be due to aural polyps, neoplasms, cholesteatomas, cholesterol granulomas or ceruminous cystomatosis.4
Otitis externa in cats: perpetuating factors
Examples of perpetuating factors include secondary infections by bacteria or Malassezia spp., contact reactions, ceruminoliths or foreign bodies, and otitis media.4 In a study conducted in Belgium, Malassezia spp. was the main microorganism isolated in the outer ear of 130 stray cats.2
Diagnosis
The diagnostic evaluation of a cat with otitis should include a medical history review, physical examination, otoscopy and exudate cytology. In addition, and depending on the predisposing or perpetuating factors in each case, laboratory tests, cultures, biopsy, X-rays or computed tomography may be indicated.1,4
Always bear in mind what is considered as normal for a cat’s ear.
A certain amount of earwax (usually dark brown, but sometimes yellowish or whitish) inside the ear is considered normal for cats. Therefore, in the absence of any clinical signs, this finding is not suggestive of otitis.
The presence of 2–3 Malassezia spp. and up to 4 cocci per field at 400x magnification is also considered normal.
Similarly, keratinocytes, nucleated keratinocytes and melanin clumps are all normal findings.
What is considered abnormal?
The presence of bacilli is usually indicative of disease, while signs of inflammatory cells are also considered abnormal.2,4
Treatment
Cleaning affected ears plays an important role in treating otitis in cats, regardless of the cause. Correct cleaning should remove any exudates and permit a more thorough examination of the auditory canal. This may require deep sedation or general anaesthesia, depending on the cat’s character. However, it is also important to remember that excessive cleaning is a predisposing factor in the development of otitis. So owners must be instructed how to clean their cat’s ear correctly and only when necessary. Some authors recommend using sterile saline solution to avoid contact reactions, while others prefer to use products with cerumenolytic properties that are approved for cats.1,4
Specific treatment for otitis should focus on eliminating the primary cause and controlling the predisposing and perpetuating factors identified in each case.
- Various acaricides are available for the treatment of otoacariasis, both for application in the inner ear (ivermectin or milbemycin) or topically, but with systemic action (selamectin, imidacloprid/moxidectin, and more recently isoxazolines).4
- Antibiotics/antifungals are indicated for patients whose cytology reveals bacteria and/or yeasts. Some authors advise against topical therapy because of the risk of contact reactions and prefer systemic treatment, even in the absence of otitis media.1 Others, however, uphold that it is very hard to treat otitis externa successfully without topical treatment and reserve a systemic approach for cases with otitis media.4
- Most topical antifungals/antibacterials also incorporate a glucocorticoid, which helps control the inflammatory process. In this regard, it has been suggested that mometasone is the topical agent with the greatest anti-inflammatory effect without demonstrating any systemic effects.4
- In cats with necrotising proliferative otitis, treatment is based on topical administration of topical or systemic tacrolimus or glucocorticoids. Studies also suggest cyclosporine may be effective.3-4
- Finally, surgical treatment is indicated in cases of otitis secondary to neoplastic masses or polyps and otitis media that does not respond to medical treatment.
Conclusions
As with many other diseases, there are significant differences in the aetiology, which is reflected in the different ways of treating otitis in cats and dogs. Although many cats with otitis externa have mites, an otoscopy should always be performed and the exudate, both fresh and after staining with Diff-Quick, subsequently examined under a microscope. In there is no response to treatment or in case of relapse, predisposing/perpetuating causes of otitis should be investigated rather than considering another therapeutic option.4,6
References
1. Kennis RA. (2013). Feline otitis: diagnosis and treatment. Vet Clin North Am Small Anim Pract; 43: 51-56.
2. Bollez A, de Rooster H, Furcas A, et al. (2018). Prevalence of external ear disorders in Belgian stray cats. J Feline Med Surg; 20: 149-154.
3. Mauldin EA, Ness TA, Goldschmidt MH. (2007). Proliferative and necrotizing otitis externa in four cats. Vet Dermatol; 18: 370-377.
4. Brame B, Cain C. (2021). Chronic otitis in cats: Clinical management of primary, predisposing and perpetuating factors. J Feline Med Surg; 23: 433-446.
5. Perego R, Proverbio D, Bagnagatti De Giorgi G, et al. (2014). Prevalence of otitis externa in stray cats in northern Italy. J Feline Med Surg; 16: 483-490.
6. Swales N, Foster A, Barnard N. (2018). Retrospective study of the presentation, diagnosis and management of 16 cats with otitis media not due to nasopharyngeal polyp. J Feline Med Surg; 20:1082-1086.
