Several ear margin dermatoses characterized by alopecia have been described in dogs. Periodic pinnal alopecia in Miniature Poodles is characterized by progressive bilateral alopecia of the convex surfaces of the ear. The hair loss is acute in onset and progresses over several months, but hair may spontaneously regrow. There are no other clinical signs. Treatment is unnecessary.
Pinnal alopecia has been reported in Dachshunds, Chihuahuas, Italian Greyhounds, and Whippets and is thought to have a hereditary predisposition. The age of onset is ≤1 yr of age. Lesions start as thinning of the hair coat, and complete pinnal alopecia may occur by 8-9 yr of age. Other commonly affected areas are the ventral neck and thorax and the caudal medial thighs. The hair loss is asymptomatic. Differential diagnoses for this condition are endocrinopathies (eg, hypothyroidism, hyperadrenocorticism, sex hormone imbalance). Histologically, the skin is normal and hair follicles are diminished in size but normal in appearance. No effective treatment has been reported, but pentoxifylline (10 mg/kg, bid-tid ), melatonin (3 mg for small breeds and 6 mg for large breeds, bid-tid ), and topical minoxidil have anecdotally been described as helpful.
Ear margin seborrhea or ear margin dermatosis is common in Dachshunds, although other breeds with pendulous pinnae may be affected. Lesions usually affect the apex of the pinnae on both sides but can progress to involve the whole ear margin. The cause is unknown. Lesions appear as waxy gray to yellow scale adherent to the base of hair shafts. Plugs of hair can be easily epilated leaving behind a shiny surface to the skin. In severe cases the ear margins are edematous, and fissured. Histologic findings include severe hyperkeratosis and follicular keratosis with dilated follicles filled with keratin debris. Differential diagnoses include sarcoptic mange, pinnal alopecia, proliferative thrombovascular necrosis, dermatophytosis, and frostbite. Dermatophytosis in particular can cause a scaling pinnal dermatitis in dogs, cats, and horses but the ear margin is not typically involved and other areas of the body are generally affected as well. Treatment includes antiseborrheic shampoos (eg, sulfur, salicylic acid, benzoyl peroxide), keratolytic products, dioctyl sodium sulfosuccinate (DSS), and systemic medications that may help normalize the abnormal keratinization process (vitamin A and synthetic retinoids; essential fatty acids). Topical or oral glucocorticoids and pentoxifylline (10 mg/kg, bid-tid ) may be beneficial when severe inflammation and fissures develop.
Several immune-mediated diseases such as pemphigus foliaceus, pemphigus erythematosus, drug eruption, toxic epidermal necrolysis, and immune vasculitis may affect the pinna and the ear canal. ( See also autoimmune skin disorders , 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 dermatopathologist. http://www.vetmanual.org/mvm/index.j...m/bc/30800.htm