The middle ear anatomy of dogs and cats is similar to that of humans. It consists of three main parts: the tympanic membrane (eardrum), the ossicles (small bones), and the eustachian (auditory) tube. The tympanic membrane is a thin sheet of tissue that separates the outer ear from the middle ear and vibrates in response to sound waves. The ossicles, consisting of the malleus, incus, and stapes bones, transmit sound vibrations from the eardrum to the inner ear. The eustachian tube connects the middle ear to the back of the throat, allowing pressure to be equalized on both sides of the eardrum. This helps prevent damage to the eardrum and hearing.
Otitis media, or middle ear inflammation, is the inflammation of the middle ear structures (the tympanic bulla, the opening of the auditory tube, and the ear ossicles). Otitis media is less common in veterinary medicine but it can occur in pets, particularly dogs and cats. Animals of various ages can be affected, and it can be unilateral or bilateral. Otitis media typically results from either pharyngeal bacteria migration into the auditory tube or infection spreading from the external ear canal through the tympanic membrane (ear drum). Occasionally, an infection may spread through the bloodstream from the inner ear to the middle ear. There have been cases of primary otitis media in some dog breeds, including Cavalier King Charles Spaniels. Otitis media left untreated can result in otitis interna (inflammation of the inner ear structures) or tympanic membrane rupture, which can cause otorrhea or otitis externa. Otorrhea is a medical term for ear leakage. Otorrhea is caused by middle ear disease with a perforated tympanic membrane or external ear canal pathology.
What causes otitis media?
Otitis media is rare in animals, and in dogs, it is most commonly caused by chronic otitis externa, which results in a descending infection (more common) into the middle ear or an ascending infection from an upper respiratory tract infection via the Eustachian tube. Iatrogenically, damage to the eardrum during ear cleaning treatment of otitis externa can also lead to the descent of infection from the outer ear into the middle ear.
With descending otitis externa, accumulated debris in contact with the eardrum leads to an eardrum that is weakened by infection and ruptures or penetrated by migrating grass seed leading to medial extension of the inflammatory process causing hyperemia and thickening of lining mucosa. There is also an accumulation of exudate in the tympanic bulla (the bony structure surrounding the middle ear structures) and thickening/sclerosis of the bulla. Medial spread causes otitis interna or, rarely, bulla osteomyelitis with the involvement of the temporomandibular joint.
With ascending otitis media, there is an upper respiratory tract infection that causes inflammatory spread up the Eustachian tube to the middle ear leading to hyperemia and thickening of the mucosa lining the tube causing accumulation of exudate, rupture of the eardrum in presence of infection resulting in ascending otitis externa and/or medial spread to cause otitis interna and (rarely) bulla osteomyelitis with involvement of temporomandibular joint. Otitis media can also be associated with nasopharyngeal polyps.
Other factors that predispose dogs to otitis media are breed specific meaning they are genetically determined, e.g., German Shepherd Dogs and breeds with long pendulous ears, eg Spaniels (English Springer Spaniel).
Otitis media affects more than 80% of dogs with chronic or recurrent otitis externa because it is not detected until it is severe.
What are the clinical signs of otitis media?
The clinical signs of otitis media include:-
Signs of otitis externa (head shaking, scratching or rubbing the infected ear, exudate, inflammation of the ear canal, persistent, refractory otitis externa),
Horner's syndrome (If the sympathetic nerves are affected, signs of Horner syndrome - enophthalmos, ptosis, miosis may be present),
Facial nerve palsy/paralysis which causes the nasal philtrum or lip to deviate away from the affected side,
Keratoconjunctivitis sicca (dry eye) together with exposure keratitis and corneal ulceration may potentially develop,
Decreased hearing or deafness due to fluid in the middle ear,
Intermittent slow head-shaking, the affected ear tilted downwards for a short time after head-shaking,
Persistent purulent aural discharge,
Otitis internal,
Involvement of the temporomandibular joint,
Circling/incoordination (vestibular syndrome),
Spontaneous horizontal or rotary nystagmus with the fast phase away from the affected side,
Head tilt, leaning or falling toward the affected side,
Lethargy and inappetence,
Fever,
Recent upper respiratory tract infection,
Irritation and pain on palpation of the external ear canal.
The vestibular syndrome is a condition that causes problems with balance and spatial orientation. It is a collection of symptoms caused by a malfunction in the vestibular system, which is part of the inner ear that regulates balance and eye movements. Dizziness, vertigo, unsteadiness, and falls are common vestibular syndrome symptoms. A variety of factors, including inner ear infections, head injuries, ageing, and certain medications, can cause the condition. The cause of the vestibular syndrome is unknown in some cases. Depending on the underlying cause, treatment for vestibular syndrome may include medication, physical therapy, or other interventions to help manage symptoms and improve balance.
These symptoms aid in differentiating otitis media from simple otitis externa. Although otitis media does not cause a neurologic head tilt, patients experiencing ear pain may tilt their heads to the side.
Many cases of otitis media in dogs are an extension of chronic otitis externa. Chronic recurrent otitis externa, particularly when it recurs quickly after the clinical and cytologic resolution, may be caused by untreated otitis media. Recurrence is more commonly caused by an uncontrolled underlying condition. Primary otitis media can also occur and is most commonly seen in Cavalier King Charles Spaniels (CKCS) as primary secretory otitis media (PSOM). The condition can be unilateral or bilateral. These dogs have shown guarded neck carriage, otic pruritus without otitis externa, and spontaneous vocalization in addition to the classic signs of otitis media. The clinical symptoms are also similar to syringomyelia, which is more common in CKCSs. Primary secretory otitis media (PSOM) in Cavalier King Charles Spaniels (CKCSs) does not appear to be gender specific, but the age at presentation is typically 3-7 years. Other small brachycephalic breeds have also been reported to have primary secretory otitis media.
Otitis media in cats is less common than in dogs, but it does occur. Otitis in cats is frequently associated with a history of respiratory disease and/or inflammatory polyps. They can develop otitis media as an extension of otitis externa less frequently.
How is Otitis Media diagnosed?
Otitis media/interna is diagnosed with a thorough history, a physical examination that identifies relevant clinical signs, and, if possible, an otoscopic examination that confirms a bulging/abnormal tympanic membrane (ear drum). Otoscopic examination of the tympanic membrane may be limited due to stenosis, ear canal anatomy, the presence of exudate, or animal or environmental constraints. Tympanic membranes that have thickened, become opaque, ruptured, or bulged may be abnormal.
Otitis media is most commonly reported in dogs with chronic otitis externa (up to 80%). It is not uncommon to have disease on both sides. Otitis media can be caused by both primary and secondary causes of otitis externa. The tympanic membrane can be intact and appear normal, making diagnosis difficult. CT or MRI imaging techniques are more sensitive than standard radiographs. Changes seen on CT/MRI include thickening, sclerosis, and lysis of the bulla's wall, as well as the bulla itself being filled with fluid/soft tissue material. Although fluid in the bullae has been found in head CTs of dogs with no history or clinical signs of otitis externa and media, diagnosis may be difficult. In some cases, the diagnosis is only made during necropsy, when the tympanic region is exposed using special techniques. When one ear is diagnosed with clinical otitis media/interna, the other ear should be examined to see if subclinical otitis is present.
What is the treatment for Otitis Media?
Treatment can be challenging and should focus on treating infections and managing inflammation. Antibiotics or other medications are typically used to clear the infection and clean the ears. Surgery may be required in some cases to correct underlying structural issues or to remove tumours. Once otitis media is suspected, the pet should be taken to the veterinarian because untreated cases can lead to chronic ear infections, hearing loss, and other complications.
Treatment of otitis media/interna is most effective when begun early in the disease's progression. If the case is severe in a dog, special consideration should be given to evaluating for a foreign body (plant awn, fox tail) or iatrogenic rupture of the eardrum, which could be caused by aggressive cleaning. Chronic cases are frequently resistant to treatment or recur after an apparent remission.
Because dogs with otitis media frequently have a history of recurrent bacterial otitis externa, exudate from the middle ear should be collected for cytology and bacterial culture. A handheld or video otoscope with a biopsy channel is preferred to ensure that the sample is taken from the middle ear (rather than the external ear, which is more likely to be contaminated).
Following sample collection, the middle ear should be thoroughly flushed with sterile saline. The cat's tympanic cavity is divided by a septum, which may make treatment more difficult. Because the eustachian tube (auditory tube) connects the middle ear to the oral cavity, these patients should always be sedated with an endotracheal tube and the cranial aspect of the body tilted down to allow fluid to flow out of the mouth (preventing aspiration). Many aerobic and anaerobic bacteria have been isolated from the ears of animals suffering from otitis media/interna, and mixed infections are fairly common. Pseudomonas spp. and Staphylococcus spp. are two bacteria that are frequently isolated in small animals.
When pathogens are identified, they should be treated topically as well as systemically whenever possible. Few products can be safely placed in the middle ear without causing ototoxicity. Fluoroquinolones, penicillins, cephalosporins, miconazole, clotrimazole, nystatin, aqueous dexamethasone, and fluocinolone are generally considered safe to use. Avoid using thick, ointment-based products. If otorrhea or otitis externa is present, the external ear canal should be cleaned and flushed in addition to antimicrobial and/or anthelmintic therapy; physiologic saline and Tris EDTA are commonly used for flushing. Steroids, both topical and systemic, can help reduce inflammation and pain associated with otitis media/interna, as well as potentially improve other clinical signs. Corneal ulceration, aural hematomas, and concurrent infections should be treated as needed, and the animal should be protected from more harm to oneself.
Due to the existence of biofilm and rising resistance, Pseudomonas spp. can be particularly challenging to treat. N-acetylcysteine and silver sulfadiazine have both been utilized in recurrent occurrences. These situations can be aggravating and may not respond to prompt, effective therapy.
Repeated middle ear flushing may be required in situations of otitis media or interna that are persistent, unresponsive, or recurrent. Eventually, a bulla osteotomy may be required to create adequate drainage and facilitate efficient lavage. After myringotomy and flushing, primary secretory otitis media in Cavalier King Charles Spaniels may become better, but it may come back over time or require more flushing.
Complete clearance of the infection and clinical indications of otitis media/interna can be achieved with early diagnosis and treatment. Owners should be informed that neurologic deficits and hearing loss may endure even after the infection has been treated in cases when the condition is severe, persistent, or nonresponsive. Otitis media in dogs and cats may require surgery (whole ear canal ablation), especially if bacteria that are resistant to many antibiotics are present.
How is Otitis Media Prevented?
Otitis media can be prevented by regular cleaning of ears, especially in dogs with pendulous or hairy ears and rigorous treatment of otitis externa, taking care not to cause iatrogenic damage to the eardrum. Cats with ear mites in the same household should be treated promptly as any infection in dogs and cats may act as a reservoir of infection.
References
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