Otitis externa

Owners notice itching and ear pain, discharge from the ear and a bad smell. The canal lining is reddened and swollen, with discharge and sometimes erosions. Chronic cases develop thickened, narrowed canals and partial to complete hearing loss. Severe, long-standing disease can involve the middle ear.

Otitis externa is inflammation of the external ear canal, and in dogs it is common and often recurrent. It is not one agent but a layered process. Primary factors such as allergic skin disease (notably atopic dermatitis), endocrine disease, keratinisation disorders and immune-mediated disease start the inflammation. Secondary microbial overgrowth follows, usually a dysbiosis of the ear's own flora rather than a new pathogen: staphylococci, Malassezia yeast, streptococci, Proteus and Pseudomonas. Over time perpetuating changes develop, beginning as nodular hyperplasia of the epidermis and ceruminous glands and progressing to canal stenosis, occlusion, fibrosis and mineralisation, which keep the disease going even after the trigger is controlled.

In UK primary-care practice about 7.3% of dogs are diagnosed with otitis externa in a year. Breed and ear carriage are the strongest risk factors: Basset Hounds have almost six times the odds, followed by Chinese Shar Pei, Labradoodles, Beagles and Golden Retrievers, while Chihuahuas and Border Collies have lower odds. Pendulous or V-shaped drop ears carry about 1.8 times the odds of erect ears. Dogs over one year old, males, and dogs at or above their breed's mean bodyweight are also at higher risk. Swimming, humidity and pinna conformation predispose without initiating disease. Repeated antibiotic exposure favours multi-resistant bacteria.

External ear canal (epidermis, ceruminous glands), pinna, middle ear, skin

Identify and manage primary disease, especially allergic skin disease; gentle ear cleaning with a dry paper cloth and judicious use of antimicrobial ear cleaners, avoiding overzealous cleaning.

Often recurrent. Long-term remission needs the primary cause, predisposing and perpetuating factors all addressed; chronic canal stenosis, fibrosis and mineralisation may leave radical ear surgery as the only option in severe cases.