Chapter 14 Diagnosis and Treatment of Otitis Media
Otitis media is a common disease process that often goes unrecognized in most veterinary practices. The fact that otitis media is present in more than half of all canine patients with chronic otitis externa should stimulate a reformulation of the diagnostic process when faced with these cases. Just the common history that the patient has been treated repeatedly for ear infections should alert the veterinarian to think about otitis media as a possibility.
The diagnosis of otitis media in dogs can be quite difficult to make, owing to the long, bent, funnel-shaped conformation of the dog’s ear canal, which makes visualizing the tympanic membrane (TM) difficult. In addition, many patients with otitis media have an intact TM, giving the clinician the impression that there is nothing wrong in the middle ear. Most canine patients with otitis media also have a chronic otitis externa with pathologic changes to the ear canal that cause stenosis, making visual examination of the TM impossible. It is often theorized that otitis media is an extension of otitis externa that was either not treated, improperly treated, or resistant to treatment. The result is significant damage, resulting in porosity to the eardrum over time.
Otitis media in cats most often results as a sequela to respiratory disease, so a history of sneezing, ocular discharge, and/or nasal discharge may provide a clue. Some cats with otitis media also have a visible polyp in the ear canal after the ear is cleaned of the dried exudates and mucus. Many feline otitis media cases have a dark, dried, crumbly exudate in the ear canal that mimics an ear mite infestation. The diagnosis of otitis media in cats may be easier to determine with the otoscope because of their relatively short ear canals.
Otitis media should be considered when the clinician is presented with a patient showing any neurologic disease affecting the head, including vestibular disease, Horner’s syndrome, or facial nerve damage.
By definition, otitis media refers to the extension of an inflammatory disease into the middle ear cavity. This may or may not be infectious. The inflammatory reaction of the mucous membrane lining the tympanic bulla is different than the reaction of the skin of the external ear, so the symptomatology and treatment of otitis media are different from those for otitis externa. The mucous membrane lining the tympanic bulla reacts to foreign substances, including infectious organisms, hair, cells, cerumen from the external ear canal, chemicals, and pharmaceuticals used in the external ear canal. It produces a purulent exudate and increases its secretion of protective mucus from activated goblet cells.
If the eardrum has a hole in it during active otitis media, copious mucoid exudate is often seen along the floor of the horizontal canal. Although this material is usually in liquid form, the mucus and pus may be inspissated and dry. Mucus is not produced anywhere along the external ear, but oozes from the tympanic bulla into the horizontal canal through any rent in the TM. The presence of mucus indicates a hole in the eardrum; precautions should be taken not to introduce ototoxic substances into the ear canal.
Otitis media in dogs is much more prevalent than previously thought. In dogs, secondary otitis media occurs in approximately 16% of acute otitis externa cases and as many as 50% to 80% of chronic otitis externa cases.1,2 Many cases of otitis media are well hidden from visual detection by the significant exudates present in the ear canal and the severe pathologic changes that have occurred in the ear canal as a result of chronic otitis externa. These changes include stenosis, fibrosis, tumors, polyps, epithelial hyperplasia, and glandular hyperplasia (Figure 14-1). Chronic changes in the external ear canal prevent adequate visualization beyond these blockages, so determining the integrity of the eardrum is not always possible.
Some dogs with otitis media have intact eardrums but also have significant bacterial and yeast populations that can be isolated from the middle ear.2 These dogs may have had a ruptured eardrum that healed, trapping bacteria and yeast in the tympanic bulla. Therefore the presence of an eardrum does not rule out otitis media. Healed eardrums trap infectious organisms in the middle ear, and suppurative otitis media results (Figure 14-2). Secretions and exudates are trapped behind the healed eardrum, causing it to bulge outward under pressure, which in turn causes severe pain. Myringotomy may be necessary to investigate the contents of the bulla in suspected cases of otitis media where the eardrum is intact.
It is uncommon for a patient to present to the veterinarian with a history of acute otitis media. However, iatrogenic rupture of the eardrum during ear cleaning can lead to an inflammatory acute otitis media. A foreign body that has become lodged in the ear canal can cause acute otitis media. Often plant awns and foxtails work their way through the eardrum and cause a considerable bacterial infection and inflammatory reaction in the ear canal.
More commonly, a dog with otitis media will have a history of recurrent or chronic bacterial external ear infections. Perhaps the pet owner will present all the external ear medications already tried on the pet; that is a signal for the veterinarian to look deeper in the ear canal for middle ear disease. Chronic otitis media is almost always suppurative, with large amounts of fluid draining into the ear canal. The presence of liquid in the ear canal may signal otitis media (Figure 14-3).
In dogs and cats with otitis media where the eardrum is open, a copious, malodorous liquid discharge is often present when the ear canal is examined with the otoscope. Some patients produce so much exudate that it overflows onto the periaural region of the face; in a floppy-ear dog, there will be dried exudate on the ear flap adjacent to the external opening of the auditory canal. Head shaking to relieve the pain and tickle associated with liquid exudate is very common in otitis media. It may be wise to check for otitis media in cases of aural hematoma. Pain on palpation of the base of the ear canal or pain on manipulation of the pinna should also alert the clinician to otitis media.
Some patients with otitis media are reluctant to have their mouth opened and may have histories of reluctance to chew hard food. This is due to inflammation, swelling, and pain within the bulla, which is located adjacent to the temporomandibular joint.
When otitis media affects the nerves that course around the base of the ear or through the tympanic bulla, the patient may show signs as subtle as keratoconjunctivitis sicca on the ipsilateral side. This results from damage to the palpebral branch of the facial nerve. When otitis media affects the sympathetic nerves from the facial and trigeminal nerves coursing through the middle ear, the patient may show mild signs of Horner’s syndrome (enophthalmos, ptosis, and miosis) (Figure 14-4). Some patients may show pain, head tilt, or, with facial nerve palsy, a drooped lip, drooped ear, or loss of the ability to close the eyelid, leading to exposure keratitis.3 Since the facial nerve courses in and around the ear canal, it is easily affected by swelling, inflammation, and trauma from the dog scratching at the base of the ear. Facial neuropathy should be suspected if there is drooping of the facial muscles and skin or drooling of saliva because the lips and facial muscles cannot create an oral seal. Peripheral vestibular disease with nystagmus and circling may be evident if the infection and inflammation have affected the inner ear.
Figure 14-4 Horner’s syndrome in a cat with cerumen gland adenocarcinoma extending into the tympanic bulla. The eyelid opening is small, the pupil is pinpoint, and the eyeball rolls inward (not pictured).
An owner may present a patient for a hearing deficit. These cases should be evaluated for otitis media. Fluid in the middle ear dampens hearing. If this fluid is the result of previous flushing, it is usually absorbed within 7 to 10 days, and the patient regains the hearing. When the eardrum is ruptured or when the ossicles of the middle ear have sclerosed, air-conduction hearing is reduced. High-pitched sound waves cannot be effectively transmitted from the ear canal to the cochlea. If a tumor or a polyp has filled the middle ear, air-conduction hearing is eliminated. Bone-conduction hearing is usually still present in these patients, but the pet can only hear the lower range of tones. (Bone-conduction hearing can be demonstrated by placing your fingers in your ears and listening to the sounds around you.) If there is hearing loss detected, this is usually as a result of bilateral ear disease. Unilateral hearing loss is difficult to assess in animals.
If there is pharyngeal drainage of mucus and exudates resulting from otitis media, the patient may be presented for inspiratory stridor. In these cases, a pharyngeal examination may reveal a nasopharyngeal polyp interfering with breathing or thick mucus draining from the auditory osteum in the nasopharynx, covering the caudal pharynx, and occluding the airway (Figure 14-5).
Figure 14-5 Pharyngeal drainage of mucus from a 12-year-old cat with mucoid otitis media. The mucus drainage is coming from under the soft palate. No organisms were cultured from this cat’s middle ear, but both bullae were sclerotic.
Otitis media with an intact, bulging eardrum may be very painful for the patient. Simply manipulating the pinna can lead to behavioral changes consistent with pain. Many dogs with otitis media cry out when the base of the skull is palpated at the junction of the ear cartilage and the skull. Some dogs even bite their owners while they are trying to administer medication because of the intense pain. Strong pain relievers are indicated in these patients. After the eardrum ruptures or is intentionally perforated by myringotomy, the pressure decreases and the pain significantly diminishes.
Careful examination of the TM in the dog or cat with otitis media requires general anesthesia. It is recommended that the patient have an endotracheal tube placed in case there is a ruptured eardrum. Manipulation or flushing can cause material to drain through the eustachian tube into the nasopharynx, resulting in aspiration.
If there is significant stenosis of the external ear canal, either from inflammation or from permanent pathologic changes to the ear canal, the eardrum may not be adequately visualized. Patient preparation using potent topical and/or systemic corticosteroids (prednisone, 1 mg/lb daily for 10 to 14 days, then taper or dexamethasone 2 mg/ml at a dose of 0.1 mg/lb intramuscularly [IM] once) may be needed to reduce otic inflammation and allow examination of the TM on a subsequent visit. If permanent changes to the ear canal prevent visual determination of the integrity of the eardrum, other techniques are used to identify disease proximal to the stenosis.
Recently, with the introduction of video otoscopes, it is possible to get a very detailed, magnified examination of the ear canal and eardrum. The video otoscope provides excellent lighting at the tip of the tapered probe by transmitting light through the probe by a fiberoptic cable attached to a high-output light source.
After the veterinarian is comfortable looking at normal eardrums—the location, color, clarity, and the normal tension on it—using the TM to diagnose otitis media becomes much easier. If the eardrum remains translucent, the middle ear can be transilluminated with the bright light from the video otoscope and the contents of the middle ear can be visualized (Figure 14-6).
Figure 14-6 Transillumination of the TM with high-intensity light allows examination of the middle ear. Air fills the normal middle ear, and a bony prominence called the promontory (behind which is the cochlea) can be seen on the medial wall of the bulla.
In obvious cases of canine otitis media, there is no eardrum present. The ear canal is filled with a liquid secretion, often with flecks of material mixed with it. A mucus-filled ear canal may alert the clinician to otitis media. Most patients with chronic otitis externa that has been present for 45 to 60 days will have a coexisting otitis media. In otitis externa, purulent exudates and proteolytic enzymes elaborated by inflammatory cells have a caustic effect on the thin epithelium of the eardrum, causing it to become necrotic, weaken, and eventually rupture. When this happens, hairs, ceruminous secretions, exudates, and infectious bacteria or yeast organisms in the external ear move into the middle ear. In these patients it is difficult to visualize any part of the eardrum, since it may not be present at all. Sometimes only a small ring of granulation tissue may be seen at the annulus fibrosus, where the eardrum attaches to the ear canal. With the otoscope, an otitis media case without suppuration looks like a deep, dark hole. The mucosa becomes dark as it becomes hyperemic, and brownish ceruminous exudates fill the bulla.
There is a condition described in dogs called a “false middle ear.” Obstructions along the horizontal ear canal from hypertrophic or cystic glands, neoplasia, inflammation, or ceruminous plugs increase pressure on the TM, causing it to stretch and bulge into the middle ear cavity. Coupled with poor air movement through the eustachian tube, negative pressure inside the bulla pulls the eardrum even farther into the middle ear cavity. A false middle ear may develop as a result of the distended membrane ballooning into the bulla. Examination of this ear also reveals the absence of an eardrum at the end of the horizontal canal. Computed tomography (CT) scans of these ears reveal a “finger” lesion protruding into the bulla. The invaginating eardrum may collect large amounts of debris from the external canal such as keratin, wax, and desquamated epithelial cells. The invaginated eardrum forms a cavity that needs to be flushed out thoroughly. Often misdiagnosed as having otitis media, these patients can be retrospectively diagnosed when on 2-week recheck the previously unseen eardrum is back in the normal location.
In some cases of otitis media the eardrum is intact, but it may look abnormal. It may change color in response to inflammation on the medial side, becoming opaque and gray in color rather than pearly and translucent. Sometimes there is fluid behind the eardrum, and examination of the intact TM may indicate that it is bulging into the external ear. Purulent material in the middle ear may be seen as yellow fluid behind the eardrum. Early polyps and tumors in the middle ear may be seen as fleshy masses through the eardrum (Figure 14-7).
Radiographic assessment of the bullae can be very helpful in determining the extent of bony involvement and the presence of increased tissue or fluid filling the bullae (see Chapter 2). However, the absence of radiographic changes in the bullae does not rule out otitis media, especially the more acute cases.
The first radiograph is taken using an open-mouth, rostrocaudal view with the x-ray beam directed through the pharynx. The tongue should be pulled rostrally to remove soft tissue that overlies the bullae. If an endotracheal tube is in place, it should be temporarily removed for this view. The procedure requires angling the mandible and maxilla to an angle of 10 to 15 degrees away from perpendicular while maintaining symmetry of the skull.
In a dog with minimal bony changes, the bullae appear as normal, eggshell-thin circular structures medial to the mandibular rami on the rostrocaudal view. The cortical outline is thin and the middle of the bullae radiolucent because the bullae are filled with air. The cat has an air-filled, two-chambered tympanic bulla separated by a bony septum.
When the bulla is chronically affected, either the intraluminal or extraluminal bone shows new bone production or remodeling. Bone lysis may be evident. The cartilage of the external canal may also be calcified and easily visible on a radiograph. Dystrophic mineralization of soft tissue surrounding the ear canal may be present. Often an entire bulla appears radiopaque because of large volumes of thick exudate or tissue growths (neoplasm, polyp, or choleasteatoma) filling the air space. If lytic lesions are present, there may be radiolucent areas or the bone constituting the bulla may be absent, as in squamous cell carcinoma or osteomyelitis. Dogs or cats with recent ventral bulla osteotomy may be identified by the absence of a segment of bone; however, bone may regrow after bulla osteotomy. One or both bullae may be affected. If unilateral disease is present, a comparison between the normal and abnormal bulla makes radiographic assessment of middle ear disease easier.
If large volumes of flushing solution are infused into the ear canal of a dog with a ruptured eardrum before radiographic assessment, a misreading of the radiograph can occur because the bullae become filled with the flushing fluid and appear radiopaque on the radiograph. One limitation of radiographic evaluation is that old sclerotic lesions in the bulla of aged animals cannot be differentiated from a more current proliferative otitis media lesion.
Computed axial tomography (CAT scan) of the tympanic bullae, where available, may aid in differentiating bony lesions in the bulla from soft tissue reactions. Many universities and teaching hospitals have access to CAT scanners. In the United States, specialty referral centers are acquiring older CAT scanners from human hospitals and may be able to provide this type of radiographic examination.
These radiographs provide views in the horizontal, vertical, and sagittal planes. CAT scans provide a number of views in these planes taken at various distance intervals, each successive view slightly farther from the previous. Each successive view may be considered as one slice of bread removed from an entire loaf, with each slice being derived from a different part of the whole.
Even when the ear canal is stenotic and otoscopic examination is impossible, CAT scans are able to give clear impressions of the status of the ear canal distal to the stenosis as well as clues to the pathology in the middle ear. Bony lesions of the bulla can be differentiated from soft tissue lesions using CAT scans. Three-dimensional measurement of the size of a lesion may be estimated by calculating the distance between successive views in different planes.
Magnetic resonance imaging (MRI) of the ear is also being done to visualize the middle and inner ears. MRI can use such fluids as the endolymph within the cochlea and semicircular canals to provide contrast to the examination. Patients with neurologic signs relating to middle- or inner-ear disease can be seen. Extension of infection into the cerebrospinal fluid space and meninges can be detected by MRI. The computer-generated images can be viewed in three planes, as with the CAT scan. At the present time, this technology is available to veterinary medicine on a very limited basis.
Several techniques have been described to determine the integrity of the TM when it cannot be visualized in an ear with a stenotic external ear canal.4 A small-diameter (3½ to 5 Fr) catheter can be inserted into the ear canal until it stops. It is then extended and retracted to get a feel for the rigidity of the “stop.” If there is a spongy feel, the eardrum is intact. If there is a definite hard feel to the “stop,” the eardrum is ruptured and the catheter is hitting the medial wall of the tympanic bulla. This technique should be practiced on cadaver specimens to acquire the necessary sensitivity.
Tympanometry uses a sensor that measures the compliance of the eardrum in response to sound waves. It is not practical to perform this test in the veterinary clinic, however, because it is still a research tool in animals.
An easy, indirect method for determining the integrity of the eardrum is to infuse warmed, very dilute povidone-iodine solution (or dilute fluorescein solution) into the ear canal with the anesthetized dog or cat in lateral recumbency. If the orange or yellow-green flushing fluid comes out of the nose or if the patient snorts out this solution through the oropharynx when pressure is applied by the flushing fluid, the eardrum is ruptured (Figure 14-8). The fluid has flowed from the external ear canal through the ruptured eardrum, into the tympanic bulla, and through the auditory tube into the nasopharynx.
Another technique used by some is to fill the ear canal of a patient in lateral recumbency with the suspected ruptured eardrum up with warmed saline and to insert the tip of the video otscope into the ear canal. By looking through the clear fluid, if air bubbles rise from the ear canal while the animal breathes, the eardrum is ruptured. Air from the nasopharynx rises through the auditory tube into the tympanic bulla to escape from the middle ear through a ruptured eardrum.
Positive contrast canalography has been described as a method for detecting a ruptured TM in dogs with otitis media.5 Two to 5 ml of dilute iodinated contrast agent is instilled into the ear canals of these anesthetized patients while in lateral recumbency with the affected ear up. The author uses 0.3 ml of Hypaque 50% or similar contrast agent in 2.7 ml of saline. In a stenotic ear canal, a 3½ or 5-Fr catheter is threaded into the stenosis if possible. Contrast agent is then infused beyond the stenosis. An open-mouth view of the bullae is then taken, using a horizontal x-ray beam. If the eardrum is intact, there will be a distinct contrast/air interface at the eardrum. If the eardrum is not intact, the contrast material will enter the bulla, and a continuous column of contrast will extend into the bulla.
In a study of this technique, eardrums of cadaver dogs with normal ear canals and intact eardrums were intentionally ruptured and contrast material was introduced into the external ear canal. In every case, contrast media entered the tympanic bulla and was detected by a radiograph. In clinical otitis media cases, positive-contrast canalography was positive in most of the cases where the eardrum was determined to be ruptured otoscopically, and it was positive for other cases in which the eardrum appeared to be intact otoscopically. In normal ears, canalography was more accurate for detecting iatrogenic TM perforation than otoscopy.5
In the cat, primary otitis media occurs as a result of infection ascending through the eustachian tube to the middle ear. The cat can also have a secondary otitis media as a result of eardrum damage from ear mites or extension of a polyp through the TM.
An exact mechanism for the development of otitis media in the cat 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 hypothesized that chronic viral upper respiratory infection early in life may play a role in initiating otitis media in cats because these infections and polyps occur in younger cats. However, this has not been documented with virus isolation studies. The presence of these viruses, however, may affect the ability of the auditory tube to protect the bulla from infection with other agents.
In many species, including humans, rats, pigs, and cattle, Mycoplasma has been reported as an inducing agent in middle ear disease.6 In addition to the more common streptococci and staphylococci isolated from clinical feline otitis media cases, organisms much more difficult to culture and identify, such as Mycoplasma and Bordetella, have also been cultured from the middle ear of cats with otitis media.7,12 It is unclear what role these upper respiratory bacteria may play in the pathogenesis of feline otitis media. It is also unclear whether anaerobic organisms may be involved when the eardrum is intact and the auditory tube swells, thus sealing these bacteria within the bulla. In the author’s experience, treatment of cats with otitis media using azithromycin (Zithromax Oral Suspension, Pfizer), which has excellent activity against both Mycoplasma and Bordetella, at a dose of 5 mg/lb every 48 hours for two or three treatments, hastens recovery from otitis media. Often, culture and/or cytology do not reveal an infectious organism. This raises the question of whether allergy, viruses, and/or fungi have a role in middle ear disease in dogs and cats.