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Otitis Media and Interna: Introduction |  |
| Otitis media, inflammation of the middle ear structures, is usually due to extension of infection from the external ear canal or to penetration of the tympanic membrane by a foreign object. It is seen in all species but is most common in dogs, cats, and rabbits. Extension of infection through the auditory tube occurs in dogs, cats, and pigs. Hematogenous spread of infection to these areas is possible but rare. Otitis media may lead to otitis interna and inflammation of the inner
ear structures. This can in turn lead to loss of equilibrium and deafness.
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| Clinical Findings and Diagnosis: |
| The signs of otitis media and otitis externa (
Otitis Externa: Introduction) may be similar. Head shaking, rubbing the affected ear on the floor, and rotating the head toward the affected side are often noted. The ear is usually painful, with a discharge and inflammatory changes in the ear canal. Because the facial and sympathetic nerves course through the middle ear, facial nerve paralysis or Horner’s syndrome (miosis,
ptosis, enophthalmos, and protrusion of the nictitans), or both, may be present on the same side as the otitis media. If there is concurrent otitis interna, head tilt toward the affected side will be more pronounced. Additionally, the animal with otitis interna may circle and fall toward the affected side and will have generalized incoordination that may be severe enough to cause difficulty in rising and ambulating. Nystagmus may also be seen with otitis interna and is
characterized as a spontaneous, horizontal to rotary type, with the fast phase away from the affected side and head tilt. Rarely, infection may ascend the vestibulocochlear and facial nerves to the brain stem and result in meningitis, a brain-stem abscess, and death.
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| Otitis media should be suspected in cases of severe purulent otitis externa; chronic, recurrent otitis externa; or whenever the tympanic membrane has been penetrated by a foreign object or has ruptured secondary to chronic otitis. The diagnosis can be confirmed by bulging, discoloration, or rupture of the tympanic membrane. Fluid in the tympanic cavity or sclerotic changes of the osseous tympanic bullae may be detected radiographically, although computerized tomography is the
imaging modality of choice for this region. Cytologic examination (Gram’s stain and Wright’s stain) and culture of the exudate may be beneficial, along with sensitivity testing of any microbial isolates. |
| Otitis interna should be strongly suspected if peripheral vestibular signs are present. Otoscopic examination and radiographs of the tympanic bulla may confirm the presence of concurrent otitis media. |
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| Treatment and Prognosis: |
| Because of the possibility of hearing loss and damage to the vestibular apparatus, longterm (3-6 wk) systemic antibacterial therapy should be instituted as soon as the diagnosis is made. Chloramphenicol, cephalosporins, trimethoprim-sulfa combinations, or fluoroquinolones should be used until the results of bacterial sensitivity tests are known. If the eardrum is ruptured, the tympanic cavity should be carefully cleaned with visualization through an otoscope and the use of long
alligator forceps, flushes of warm saline, and low vacuum suction. Small perforations of the eardrum usually heal in 2-3 wk. Any associated otitis externa should be treated concurrently. Additionally, anti-inflammatory doses of glucocorticoids (0.5 mg/kg/day) during the first 5-7 days of treatment may decrease inflammatory changes in the vestibulocochlear, facial, or sympathetic nerves. |
| In animals with otitis media and interna in which the external ear is clean and normal, but the tympanum is bulging or discolored, it may be advantageous to perforate the tympanum (perform a myringotomy) to permit culture of the fluid, to relieve the pressure (and thus the pain) within the middle ear, and to permit removal of the inflammatory exudate; however, perforation of the tympanum could result in permanent diminished hearing loss. Systemic antibiotic therapy based on
sensitivity testing should be continued for 3-4 wk and possibly up to 6 wk if otitis interna exists. In chronic otitis media, if radiographic changes are consistent with osteomyelitis or fluid in the tympanic bulla, a bulla osteotomy is usually necessary to allow for drainage and adequate resolution of the infection. |
| Otitis media with an intact tympanum usually responds well to systemic antibiotic therapy; however, if chronic otitis externa exists and the tympanum is ruptured, the chances of successful treatment are reduced. If facial and sympathetic nerve deficits develop, they may persist even after the infection has been cleared. Otitis interna usually responds well to longterm antibiotic therapy, but some neurologic deficits (eg, incoordination, head tilt, deafness) may persist for
life. Animals recovering from otitis interna should be given adequate time to adapt to any persistent neurologic deficiencies. |
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