Perpetuating factors in essence “keep the pot stirred” and prevent healing. The most common perpetuating factors are bacterial and yeast infections (see Box 32-1). Infection with a resistant organism is an increasingly common cause of recurrent otitis externa in dogs and cats. Severe inflammation leading to thickening, stenosis, and damage to epithelial migration as a result of the primary disease can be a perpetuating factor that favors the growth of secondary microbial infections. Undiagnosed OM is a common cause of recurrent otitis externa.

CLINICAL SIGNS

Otitis externa (OE) describes inflammation of the external ear canal from the pinna to the tympanic membrane (TM). This is the most common presentation of otitis in cats, and clinical localization of the disease usually is not difficult based on history and clinical examination. OE in cats may present with, but is not limited to, any combination of the following clinical signs: erythema, hair loss, scaling, crusting, pruritus, pain, deformed ear pinna, thickening of the external pinna, odor, and/or exudate of variable color, amount, and consistency. The owner may report head-shaking, ear-twitching, fits of ear-scratching after manipulation of the ear, changes in eating habits, changes in behavior (e.g., hiding or aggression), or changes in vocalization. Clinical signs may be unilateral or bilateral, persistent or intermittent, and acute or chronic. The initial presenting complaint may be unrelated to the ears; some cats are presented because of facial lesions. Otitis media is a common complication in cats with severe OE.

Otitis media (OM) is inflammation of the middle ear cavity including the TM and bulla. Many but not all cats with OM have concurrent OE. OM always should be suspected when cats present with severe purulent OE and chronic recurrent OE. Cats with OM without signs of OE may be presented for head-shaking, pawing at the ear, pain when the head is touched, changes in eating habits or appetite, pain when the mouth is opened, depression, and loss of hearing. Clinical signs may be unilateral or bilateral. Otoscopic examination of the ear canal typically reveals exudate and inflammatory changes in the canal when OE also is present. Manual manipulation of the ear usually is painful, and a squishing sound is common, indicating fluid in the canal. If the TM can be visualized, bulging, discoloration, and/or rupture may be seen. OM can be present without signs of OE, but the TM almost always appears abnormal. Cats with OM and a ruptured TM often have copious malodorous liquid discharge on otoscopic examination. This also may be seen on the floor of the horizontal canal. Mucus may be seen with OM. It is important to note that mucus normally is not present anywhere along the external ear canal, but it does ooze from the tympanic bulla through any tear in the TM. If mucus is present on otoscopic examination of the external canal, then there is a tear in the TM.

Most dermatologists agree that OM is less common in cats than in dogs. This may be because of a species difference, or it may be because it is underrecognized. In the authors’ referral practice, dogs are presented for OM far more commonly than cats. However, in one of the authors’ (KM) experience with treating cats at animal shelters, severe OE and OM were far more common compared with the pet cat population. In this environment cats with untreated OE often developed OM. Chronic ear mite infestation was another major cause of OM in cats. OM also was a common complication in cats with, or recovering from, upper respiratory infections. OM can be present even if the TM is intact. Ascending infections through the eustachian tube can cause OM in cats. Chronic sinusitis can lead to bulla effusion and OM in cats.

Otitis interna (OI) describes inflammation of the bony labyrinth where the organs of hearing (cochlea) and vestibular apparatus (semicircular canals and vestibule) are located.⁶ Loss of hearing, head tilt, circling, falling, generalized incoordination, difficulty rising and ambulating, nystagmus, facial nerve paralysis, and Horner’s syndrome are common signs in cats with OI. In cases of concurrent OM, head tilt is toward the affected side and the cat may circle and fall toward the affected side. Nystagmus may be spontaneous, horizontal, or rotary, with the fast phase away from the affected side and head tilt. OI owing to an infection can be the result of an ascending infection through the eustachian tube or secondary to OM with or without complicating OE. When vestibular signs are associated with concurrent signs of OE/OM, it is reasonable to assume the cat’s OI is the result of this infection. What is most problematic is the cat presenting with signs of OI in the absence of signs of OE/OM. These patients require an aggressive diagnostic evaluation to determine if the vestibular signs are peripheral or central.

DIAGNOSIS

Unlike other skin diseases, it is not usually difficult to identify the primary dermatological problem as otitis. What can be difficult, however, is determining the extent and severity of the otitis and the primary cause. Clients need to understand that the primary cause may not be evident until secondary infections and predisposing factors are identified, treated, and eliminated (if possible). Furthermore, the primary cause may not be a condition unique to the ear; rather, the otitis may be a manifestation of a larger skin disease. The diagnostic evaluation of a cat with ear disease is typical of all skin diseases: careful collection of historical information, examination of the patient and ears, and otic-specific diagnostic tests.

HISTORY

Important historical findings to determine include details on the onset, duration, and progression of the ear disease. Features such as whether or not it is unilateral or bilateral are important. For example, unilateral ear disease is more compatible with foreign body, ear tumors, or polyps than with allergic disease. Presence or absence of seasonality is important, because allergies are common causes of ear disease in cats. Age of the patient also is important. Young animals are predisposed to parasites, adult animals are prone to allergic disease, and old animals are predisposed to tumors and immune-mediated diseases. Evidence of contagious parasites should be assessed in all cats; fleas and mites commonly affect the head, neck, and ears. Knowledge of the cat’s source and lifestyle are important. Recently acquired animals from shelters may have underlying medical conditions. Free-roaming cats are at increased risk of contagious diseases (e.g., dermatophytosis, ectoparasites). Viral status is important because chronic OM is often linked to retrovirus and upper respiratory infections. Response to prior treatments and frequency of ear cleanings are valuable information.

In a busy practice this information is collected most efficiently using a history form. History forms are used commonly for new patients; however, they also are very valuable for chronic patients. Prior to referring patients to a specialist for a chronic ear problem, the primary care veterinarian should ask the client to fill out a history form. This retrospective view of the patient may reveal patterns and a diagnosis that otherwise were not obvious and may save the client the time and money of a referral. Clients often are resistant to filling out these forms because “it’s all in the medical record.” A brief explanation that the medical record reflects the veterinarian’s view of the case and the history form reflects their view of their pet’s ear disease usually is a convincing enough argument to get the client’s cooperation.

PHYSICAL EXAMINATION

A general examination of the patient is needed to determine if the ear disease is the only clinical abnormality, or if there are other concurrent dermatological or medical problems. Special attention should be paid to the presence or absence of neurological signs. At some point in the examination the oropharynx and larynx must be examined for nasopharyngeal polyps. Signs of systemic disease should be noted because otitis may be a component of some paraneoplastic diseases. Some neoplasias in cats will present with concurrent otitis (e.g., mast cell disease) (see Chapter 67).

OTIC EXAMINATION

A detailed description of the anatomy and examination procedures of the feline ear is presented in Chapter 30. Whether or not examination of the ear can be done without sedation depends on the patient and severity of the ear disease. Rarely can a truly adequate otoscopic examination be performed if the cat is painful or struggling, and sedation is commonly needed even in cats with OE alone. Clients need to be reminded that OE, OM, and OI can be present alone or in combination, and that imaging (see Chapter 31) often is needed before the true severity of the ear disease can be determined.