Symmetrical noninflammatory alopecic disorders affecting the pinna, such as periodic pinnal alopecia, pattern baldness, and alopecia associated with melanoderma, may affect dogs and cats and are typically idiopathic.
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 throughout several months, but hair may spontaneously regrow. There are no other clinical signs. A similar condition was reported in Siamese cats in which complete or patchy alopecia of the convex aspect of both pinna develops. Treatment is unnecessary.
Pattern baldness affecting only the pinna 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. Histologically, the skin is normal, and hair follicles are diminished in size but normal in appearance. No effective treatment has been reported, but pentoxifylline (15–20 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. Pattern baldness restricted to the pinna has also been reported in cats; however, use of minoxidil in cats should be avoided, because it has been associated with death in two cases.
Alopecia associated with melanoderma has been described mostly in Yorkshire Terriers and occasionally in Doberman Pinchers. Alopecia and marked hyperpigmentation (melanoderma) are first noticed between 6 mo and 3 yr of age and affect both pinna and the bridge of the nose. Other areas such as the tail and feet may also be affected. The alopecic and hyperpigmented skin has a smooth, shiny, and leathery appearance. The condition tends to worsen as the dog ages, and it typically does not spontaneously resolve. There is no treatment.