Several immune-mediated diseases such as pemphigus foliaceus, pemphigus erythematosus, drug eruption, toxic epidermal necrolysis, and immune-mediated vasculitis may affect the pinna and the ear canal. (Also see Immunologic Diseases: Autoimmune Skin Disorders.) Other areas of the body are typically affected and may include footpads, mucous membranes, mucocutaneous junctions, nails and nail beds, and the tip of the tail. Immune-mediated diseases are confirmed with biopsy of primary lesions (papules, vesicles, pustules, erythematous margins of secondary lesions) with histologic evaluation by a dermatohistopathologist.

Acquired folded ear tips in cats are most often associated with longterm glucocorticoid therapy (eg, daily eye or otic preparations). It may also be caused by solar radiation damage. Ear folding may not be reversible.

Feline solar dermatitis or actinic dermatitis is seen most commonly in white cats or cats with white pinnae that have been chronically exposed to sun. Lesions first appear as erythema and scaling on the sparsely haired tips of the ears. Crusting, exudation, and ulceration may develop as the actinic keratosis undergoes transformation into a squamous cell carcinoma. During early stages of the disease, treatment consists of limiting exposure to ultraviolet light through confinement indoors between the hours of 10 am and 4 pm, and the use of topical sunscreens. Squamous cell carcinoma of the pinnae is treated with surgical excision followed by radiation therapy. If surgery and radiation therapy are not an option, topical treatment with imiquimod cream, 2–3 times weekly has shown promising results.

Proliferative thrombovascular necrosis of the pinnae is rare in dogs. There are no known breed, sex, or age predilections, and the etiology is unknown. Lesions, which consist of scaly, thickened, hyperpigmented skin surrounding a necrotic ulcer, begin at the apex of the ear and spread along the concave surface. Eventually, necrosis may deform the margin of the pinna. Pentoxifylline (10–15 mg/kg, bid-tid) and/or the combination of tetracycline and niacinamide (250 mg or 500 mg of each for dogs <10 kg and ≥10 kg body wt, respectively, tid) have been anecdotally reported to be efficacious in some cases.

Auricular chondritis has been reported rarely in cats and dogs. Clinical signs include pain, swelling, erythema, and deformation of the pinnae. Both ears are typically affected. Systemic signs may accompany some cases. Histologically, lesions consist of lympho-plasmacytic infiltrates, basophilia, and loss or necrosis of cartilage. Treatment may not be required if the condition is nonpainful and no systemic signs are present. Oral glucocorticoids have been reported to be ineffective, but dapsone (1 mg/kg, sid) has induced remission in some cases.

Vasculitis is an uncommon disorder of dogs and cats. Lesions consist of erythema, well-demarcated ulcers, crusts, and sloughing of necrotic tissue. The pinnae, tail, and footpads are typically affected. It is usually difficult to determine the triggering cause, which may be immune-mediated, drug-induced, concurrent infection, neoplasia, or idiopathic. Treatment involves identifying and eliminating the inciting cause, systemic glucocorticoids, tetracycline and niacinamide, pentoxifylline, dapsone, and cyclospor-ine or other immunomodulating drugs.

Frostbite may occur in animals poorly adapted to cold climates and is more likely in wet or windy conditions. It typically affects body regions that are poorly insulated, including the tips of the ears, feet, and tail. The skin may be pale or erythematous, edematous, and painful. In severe cases, necrosis and sloughing of the ear tips may follow. Treatment consists of rapid, gentle warming and supportive care. Amputation of affected regions may be required but should be delayed until the extent of viable tissue is determined.

Canine juvenile cellulitis is an uncommon disorder of puppies and is characterized by, sterile papules, nodules, and pustules of the face and pinnae, in addition to submandibular lymphadenopathy. It occurs in puppies 3 wk to 4 mo old and rarely in older animals. Golden Retrievers, Gordon Setters, and Dachshunds appear to be at greater risk than other breeds. A purulent otitis externa is common, along with edematous, thickened pinnae. Systemic signs such as anorexia, lethargy, and fever may be present in some cases. The diagnosis can be confirmed by biopsy, which shows a pyogranulomatous inflammatory infiltrate with no microorganisms, and by negative bacteriologic culture. Early treatment is recommended to avoid scarring. Prednisone or prednisolone (2 mg/kg, PO, divided bid) should be tapered slowly over 4–6 wk or until the disease is inactive. Antibiotics may be needed to treat secondary bacterial infection.

Last full review/revision July 2011 by Sheila Torres, DVM, PhD, DACVD; Scott A. Dee, DVM, MS, PhD, DACVM