Section: Information In-depth
Causes
Inhalant allergy is extremely common in cats and is the most common underlying cause for recurrent otitis externa. Clinical signs are initially seasonal. Progressive worsening with time is also typical. At least 50 percent of these cats have bilateral otitis externa. In up to 5 percent of cases, otitis may be the only complaint. These cats tend to have itchy feet, itchy face and itchy ears. They are predisposed to secondary skin and ear infections that tend to recur after treatment unless the underlying allergy is well controlled.
Food allergy. Over 20 percent of these cases start with just otitis externa and ear disease is present in 80 percent of the cases. It should be considered as a top differential for otitis externa in any cat less than one year of age. Food allergy, however, can occur at any age and may mimic clinical signs of inhalant allergy. These animals tend to have recurrent skin and ear infections unless the underlying allergy is identified and addressed.
Foreign bodies. Plant material (fox tails) dirt, sand, impacted wax, loose hair and dried medications are frequently responsible for ear infections. In most cases this is a unilateral otitis, which means it only affects one ear.
Diseases of keratinization, such as primary seborrhea of cocker spaniels. Follicular casts and scales are found on physical exam and secondary skin infections occur commonly as the excessive amount of lipids is an optimal medium for bacteria and yeast to proliferate.
Endocrine disorders. Hypothyroidism and Cushing's disease are the most common endocrine diseases that can cause otitis externa. If a middle-aged cat keeps relapsing with otitis externa and is not itchy, then endocrine disease should be considered as a possible underlying cause.
The ear mite (Otodectes cynotis). In cats, the incidence is controversial but most veterinarians agree that it is responsible for 5 to 10 percent of cases. In recurrent cases it is possible that others in contact with animals can act as asymptomatic carriers. It is hypothesized that hypersensitivity may induce severe inflammation that is sometimes seen in some cases, especially when few or no mites are found.
Most cases (over 80 percent) of chronic or relapsing otitis externa have otitis media. This results from chronic inflammation of the external part of the ear canal, rupture of the tympanic membrane and establishment of infection in the middle part of the ear.
Discharge in the middle ear cavity is difficult to treat with topical therapy and often remains a source of infection. Otitis media is usually bacterial in origin.
Treatment of otitis media is based on bacterial culture and sensitivity results. Most cases require long term antibiotic therapy (minimum of two months) and aggressive topical therapy.
Most causes of otitis externa are associated with generalized dermatologic conditions. A complete dermatologic history and work-up may therefore be necessary in the diagnosis of many primary otitis externa cases. The most common causes seen in dermatology are atopy (inhalant allergies), food allergy, diseases of keratinization (e.g. primary seborrhea of cocker spaniels), and ear mites. It is critical to long term management of otitis externa that a primary cause can be found.
Related Symptoms
Clinical signs suggestive of otitis media include head shyness and pain on palpation of the ears. Some cases of otitis media might present with head tilt, circling and dry eyes, but the vast majority do not have neurological abnormalities.
As the ear drum quickly grows back after rupture, otitis media may also be present even if an intact membrane is seen on otoscopic examination. X-rays cannot be used to completely rule out the presence of otitis media since 25 percent of confirmed cases had no radiographic evidence of the disease.
In most cases of chronic otitis externa/media bacteria such as Staphylococcus and Pseudomonas are present. The color, texture and odor of the exudate from a diseased ear can provide clues regarding the underlying primary cause of the otitis and the perpetuating factors that may be involved. A dark, moist brown discharge tends to be associated with bacteria and yeast infections. Purulent creamy to yellow exudates are most often seen with bacteria such as Pseudomonas.
Related Articles
-
1
Aural Hematoma in Cats
Aural hematoma is an accumulation of blood within the cartilage layers of the ear. This problem is most often associated with underlying ear disease, like excessive head shaking, that can rupture blood...
» Read More
-
2
Otitis Externa in Cats
Otitis externa is a condition characterized by inflammation of the soft tissue components of the external ear canal. It is characterized by inflammation of the soft tissue components of the external ear...
» Read More
