Otitis Media and Interna in Animals
Otitis media, inflammation of the middle ear structures, is seen in small and large domestic animals, including dogs, cats, rabbits, ruminants, horses, pigs, and camelids. It can be unilateral or bilateral and can affect animals of all ages. Although typically sporadic, outbreaks are possible in herds. Otitis media usually results from extension of infection from the external ear canal through the tympanic membrane or from migration of pharyngeal microorganisms through the auditory tube. Occasionally, infection extends from the inner ear to the middle ear, or reaches the middle ear by the hematogenous route. Primary otitis media has been reported in certain breeds of dogs, particularly Cavalier King Charles Spaniels. Untreated otitis media can lead to otitis interna (inflammation of the inner ear structures) or to rupture of an intact tympanic membrane with subsequent otorrhea or otitis externa.
Clinical findings of otitis media include:
Signs of otitis media frequently include those of otitis externa (head shaking, rubbing or scratching the infected ear, exudate in the ear canal). If the sympathetic nerves are affected, there may be signs of Horner syndrome (enophthalmos, ptosis, miosis). Keratoconjunctivitis sicca and facial nerve palsy are also possible, with exposure keratitis and corneal ulceration also potentially developing. With facial paralysis, the nasal philtrum or lip may deviate away from the affected side. These signs help to distinguish otitis media from simple otitis externa. Some owners may notice deafness due to fluid in the middle ear. Otitis media does not cause a neurologic head tilt, but patients with ear pain may hold their head to the side.
In dogs, many cases of otitis media are an extension of chronic otitis externa. Cases of chronic recurrent otitis externa, especially those that recur quickly after clinical and cytologic resolution, may be due to untreated otitis media. More commonly, recurrence is because the underlying condition has not been controlled. Primary otitis media can also occur and is seen most commonly as primary secretory otitis media (PSOM) of the Cavalier King Charles Spaniel (CKCS). The disease may be unilateral or bilateral. These dogs will present with classic signs of otitis media but have also demonstrated guarded neck carriage, otic pruritus without otitis externa, and spontaneous vocalization. The clinical signs also overlap with syringomyelia, which is more common in CKCSs. There does not seem to be a sex predilection for PSOM in CKCSs, but age at presentation is typically 3–7 years. Primary secretory otitis media has also been reported in other small bracheocephalic breeds.
Otitis media is less common in cats than dogs but does occur. Cats with otitis frequently may have a history of respiratory disease and/or inflammatory polyps. Less commonly, they can develop otitis media as an extension of otitis externa.
Otitis media can also occur in large animals, including ruminants, horses, pigs, and camelids. Mycoplasma bovis is increasingly recognized as a cause of otitis media, respiratory disease, arthritis, mastitis, and other diseases in cattle. Otitis media associated with M bovis occurs in dairy and beef calves. Affected calves may be febrile, anorectic, develop ear droop/pain, exhibit head shaking, and develop other signs of facial nerve paralysis. Unilateral otitis media is more common, but bilateral disease can occur. Otitis media is uncommon in horses, but severe otitis media/interna can result in fusion and fracture of the tympanohyoid joint; extension of the fracture line to the calvarium can lead to intracranial spread of infection or cause hematoma and death.
Clinical findings of otitis interna include:
With otitis interna, inflammation impairs function of the vestibulocochlear nerve (cranial nerve VIII), resulting in hearing loss and signs of peripheral vestibular disease such as:
Extension of infection from the inner ear to the brain leads to meningitis, meningoencephalitis, or abscesses, with signs referable to those conditions.
Whereas animals with otitis media or interna are usually alert, nonfebrile, and have a good appetite, those with meningitis or meningoencephalitis are usually depressed, febrile, and inappetent. A major differential diagnosis for otitis media/interna in ruminants is listeriosis. However, in listeriosis, cranial nerves other than VII and VIII may be affected, causing signs such as dysphagia or loss of facial sensation, and affected animals are usually depressed.
Diagnosis of otitis media/interna begins with a complete history, physical examination identifying applicable clinical signs, and, when possible, otoscopic examination confirming a bulging/abnormal tympanic membrane. Otoscopic evaluation of the tympanic membrane may be limited due to stenosis, anatomy of the ear canal, presence of exudate, or animal or environmental limitations. Abnormal tympanic membranes may thicken, become opaque, rupture, or bulge. The pars flaccida is located on the dorsal aspect of the tympanic membrane and may bulge due to increased pressure from air, fluid, or soft tissue. However, the tympanic membrane may look normal or intact in some cases of otitis media, and bulging caused by air can be found in some normal animals. Video otoscopy may help to better visualize the tympanic membrane, but viewing the middle ear is difficult without a small arthroscope.
In dogs, otitis media is reported most commonly in patients with chronic otitis externa (up to 80%). Bilateral disease is not uncommon. Primary and secondary causes and factors of otitis externa can lead to otitis media. Diagnosis can be challenging, because the tympanic membrane can be intact and appear normal. Palpation of the tympanic membrane with a blunt instrument is not an accurate method of determining the patency of the tympanic membrane. Advanced imaging techniques (CT or MRI) are more sensitive than routine radiographs. On CT/MRI, changes include thickening, sclerosis and lysis of the wall of the bulla, as well as the bulla itself filled with fluid/soft tissue material.
In large animals, otitis media and interna are presumptively diagnosed based on history and clinical signs. A history of bottle feeding or feeding of contaminated milk to neonates, concurrent or previous respiratory disease, chronic ear infection, or aural foreign body, in conjunction with typical signs of otitis media/interna, should prompt examination of the ear canal. Radiography can detect osseous changes in the tympanic bulla and fluid in the tympanic cavity if appropriate positioning and techniques are used. However, CT and MRI are more sensitive and are the preferred methods when feasible. Fluid in the bullae has also been found in head CTs of dogs with no history or clinical signs of otitis externa and media, however, so diagnosis may not be simple. In some cases, diagnosis is made only at necropsy, using special techniques to expose the tympanic region. Diagnosis of clinical otitis media/interna in one ear should always prompt examination of the other ear to determine whether subclinical otitis is present.
Treatment of otitis media/interna is most successful when started early in the course of the disease. If the case is acute in a dog, then special consideration should be given to evaluation for a foreign body (plant awn, fox tail) or iatrogenic rupture of the eardrum, possibly secondary to aggressive cleaning. Chronic cases are often refractory to treatment or recur after apparent remission.
Because dogs with otitis media often have a chronic history of recurrent bacterial otitis externa, samples of exudate from the middle ear should be taken for cytology and bacterial culture. To ensure the sample is taken from the middle ear (and not the external ear which is more likely to be contaminated), use of a handheld or video otoscope with a biopsy channel is preferred.
If the tympanic membrane is intact, a myringotomy can be performed using a sterile, rigid polypropylene catheter cut at a 60-degree angle, a long spinal needle, a curette, or even a CO2 laser. The membrane should be punctured at the 5–7 o'clock position to avoid the blood supply of the tympanic membrane, which is more dorsal. It is important to maintain the vessels to allow for healing and regrowth of the tympanic membrane. Fluid and exudate can then be removed aseptically from the middle ear using a catheter, and that sample can be submitted for culture to select an appropriate systemic antibiotic. After sample collection, the middle ear should be flushed copiously with sterile saline. The tympanic cavity in the cat is divided by a septum, which may make treatment more challenging. Because the eustachian tube connects the middle ear to the oral cavity, these patients should always be under general anesthesia with an endotracheal tube, with the cranial aspect of the body tilted down to allow flow of fluid out of the mouth (preventing aspiration). If general anesthesia is not possible the procedure can be done under heavy sedation, but this is less safe. Some patients may have worsening of clinical signs acutely after flushing of the middle ear.
Many aerobic and anaerobic bacteria have been cultured from the ears of animals with otitis media/interna, and mixed infections are common. Bacteria that are frequently isolated include:
Which of these bacteria are pathogenic is unclear. Studies have shown that tympanic bullae are not sterile and often have oral flora (which makes sense because the bulla are connected to the oral cavity via the Eustachian tubes).
Once specific pathogens are identified, they should be treated both topically and systemically when possible. There are few products that can be safely placed in the middle ear without risk of ototoxicity. In general, fluoroquinolones, penicillins, cephalosporins, miconazole, clotrimazole, nystatin, aqueous dexamethasone, and fluocinolone are safe to use. Thick, ointment-based products should be avoided. Tris EDTA as a flushing agent is safe to use. No antimicrobial agents are labeled for treatment of otitis media/interna in food-producing animals in the USA, so extralabel drug use guidelines must be followed and prohibited drugs avoided.
In addition to antimicrobial and/or anthelmintic therapy, the external ear canal should be cleaned and flushed if otorrhea or otitis externa is present; physiologic saline and Tris EDTA are commonly used for flushing. Topical and systemic steroids can help reduce inflammation and pain associated with otitis media/interna and may potentially improve other clinical signs. Corneal ulceration, aural hematomas, and concurrent infections should be treated appropriately, if present, and the animal protected from further self-injury.
Pseudomonas spp can be particularly difficult to treat due to the presence of biofilm and increasing resistance. Silver sulfadiazene has been used in recurrent cases, as has N-acetylcysteine. These cases can be frustrating and may not respond to aggressive, appropriate treatment.
M bovis is particularly problematic in dairy calves fed unpasteurized waste milk from cows with intramammary infection.
In chronic, nonresponsive, or recurrent cases of otitis media/interna, repeated flushing of the middle ear may be necessary. It may ultimately be necessary to perform a bulla osteotomy to establish sufficient drainage and enable effective lavage. Primary secretory otitis media in Cavalier King Charles Spaniels may improve after myringotomy and flushing but can recur with time or require repeated flushing.
Early diagnosis and treatment of otitis media/interna can result in complete resolution of infection and clinical signs. However, with severe, chronic, or nonresponsive cases, owners should be advised that neurologic deficits and hearing loss may persist even if infection is resolved. In dogs and cats, otitis media may require surgery (total ear canal ablation), particularly if multidrug-resistant bacteria are present.
Otitis media and interna are uncommon in animals.
In dogs, they are most commonly the result of chronic otitis externa.
Diagnosis requires history, otoscopic and physical examination, and advanced imaging, if possible.
Treatment can be difficult and should be directed at treating infections and managing inflammation.