The Use of Corticosteroids in Otitis Media
When the character of the middle ear secretions is mucoid and cultures do not reveal a bacterial infection, aqueous topical corticosteroids such as dexamethasone sodium phosphate (DMSO, 4 mg∕ml) or a DMSO∕fluocinolone combination (Synotic, Ft.
Dodge) may be infused through a catheter placed in the cleaned and dried bulla. These potent topical antiinflammatories are not ototoxic. Other potent injectable topical corticosteroids are formulated with such ototoxins as benzyl alcohol or propylene glycol, or they are in suspension. These should not be used in the bulla.Corticosteroids slow the intense inflammation and exudation found in middle ear disease. As described earlier, the mucoperiosteum undergoes severe pathologic changes in response to inflammation. Corticosteroids can reverse some of the extensive granulation that forms in the bulla, enhancing the ability of topically applied antibiotics to penetrate into the infected tissue. The tympanic cavity is crowded out by this hyperemia and proliferating granulation tissue, so the amount of free space within the bulla decreases. Reducing the inflammation helps this lining membrane retract back toward the bone, increasing the volume within the bulla. When the eardrum heals, this space should refill with air.
Corticosteroids reduce the amount of mucus produced in the bulla and decrease the viscosity of the secretions from the inflamed mucous membrane in the bulla. Changing the character of the mucus aids in its removal. Thickened, tenacious, inspissated material is more difficult to remove than thin mucus. Corticosteroids may also reduce the swelling in the auditory tube, increasing lumen diameter, which has the beneficial effect of offering limited drainage of mucus into the nasopharynx.
If there is bacterial or fungal disease and the space in the bulla is needed for antibiotic or antifungal topical therapy, decreasing doses of systemic corticosteroids may be used for a few weeks during the recovery phase of otitis media. The high initial doses of corticosteroid required mirror the doses used for such other diseases as inflammatory bowel disease.
Patients should be screened for diabetes, Cushing’s disease, demodicosis, and potential pregnancy before using high doses of corticosteroids. Prednisone or prednisolone at 1 to 2 mg/lb daily for 2 weeks then decreasing to 1∕2 mg/lb every other day provides high enough levels to decrease inflammation within the bulla. Owners of these animals need to be warned that there will be side effects of prednisone at such a high dose. Many owners discontinue the medication when the side effects occur. The author prefers to use a 0.1 mg/lb intravenous dose of dexamethasone (2 mg∕ml) at the time of treatment and then repeat this injection weekly at the recheck appointment if there is significant exudate that needs to be suctioned from the bulla. (The presence of exudate indicates continuing inflammation in the membrane.) This prevents the owners from having the choice to stop the medication. Dexamethasone has a higher degree of antiinflammatory activity than prednisone and has no mineralocorticoid activity, which minimizes the undesirable side effects (polyuria/polydypsia) seen with prednisone. Dexamethasone, however, depresses the pituitary-adrenal axis.Because many dogs with otitis media also have concurrent otitis externa, systemic corticosteroids aid in reducing the swelling and pain from otitis externa. In addition, they reduce the signs associated with atopic disease, which is a primary cause of otitis externa in the dog.
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