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EAR DISEASES OF THE DOG AND CAT
AETIOPATHOGENESIS OF OE
Predisposing factors include:
Figure 4. Seborrhoeic otitis in a Shih Tzu bitch with ovarian imbalance.
Breeds with narrow ear canals: Chow Chow, Shar Pei. Auricular hypertrichosis: Bichon, Poodle, Shih Tzu (Fig. 5). Previous episodes of otitis, causing stenosis. Seborrhoeic conditions: German Shepherd. Breeds with pendulous ears: Cocker Spaniel, Basset Hound. Excess moisture: Dogs that swim, damp climates. Polyps: In cats, nasopharyngeal polyps. Ceruminous gland neoplasms. A long, narrow horizontal canal: German Shepherd. Apocrine cysts: In dogs. Apocrine cystadenomatosis: In cats. Poor care: Baths without protecting the EEC, over-zealous cleaning of the EEC with cotton buds or similar.
Perpetuating or secondary factors include:
Figure 5. Obstruction of the canal by knotted hair. Photograph courtesy of Dr Ana Ríos.
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Secondary infections by bacteria and/or yeasts: The most commonly isolated bacteria are Staphylococcus intermedius, Streptococcus, Proteus spp., E. coli, Klebsiella and Pseudomonas spp. Ulcers and a yellowish-white exudate are common with Gramnegatives. The most important yeast is Malassezia pachydermatis. Overgrowth tends to be found in cases of allergy, damp environments, and after antibiotic treatment. Otitis media: Inflammation of the tympanic bulla can cause recurrent OE with an apparently healthy eardrum. Pathological changes to the external ear: Closure of folds and accumulation of scales and secretions, causing a reversal of epithelial migration. Drug reactions: Reactions to neomycin are the most common; gentamicin and vehicles such as propylene glycol are less commonly involved.
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