Symmetrical Pinnal Alopecia

Alopecia can be a primary or secondary lesion. Secondary alopecia caused by trauma is the most common cause of alopecia of the pinna. Trauma includes fight wounds, physical or chemical trauma, and self-inflicted trauma as in the pruritic dermatoses detailed earlier.

The new classification of primary canine alopecia proposed by Mecklenburg (personal communication, 2002) can be applied to the ear pinnae:

• Inflammatory alopecias, such as the immune-mediated (vasculitis, dermatomyo­sitis) and infectious causes (dermatophytosis, bacterial folliculitis, demodicosis). The infectious causes are usually not symmetrical.

• Noninflammatory alopecias, such as disorders of the hair-follicle cycle (pattern alopecia, cyclic alopecia, postclipping alopecia, endocrinopathy, telogen/anagen defluxion), dystrophic alopecia (traction alopecia), and alopecia caused by struc­tural defects of the hair shaft (color dilution alopecia and other follicular dysplasias, congenital alopecia)

The noninflammatory causes of primary alopecia affecting the ear pinna are described together because symmetrical alopecia is the main feature of these diseases. Other causes are described previously.

Pattern Baldness

A type of pattern baldness restricted to the pinnae is described primarily in male Dachshunds, but also in other breeds of dogs (Chihuahuas, Boston Terriers, Whippets, Italian Greyhounds, Staffordshire Bull Terriers); it has been reported in cats as well.

Bilateral symmetrical hypotrichosis begins when the dog is about 1 year old and can remain unnoticed for some years. As the alopecia evolves, the underlying skin becomes hypopigmented. According to Scott,¹⁴ pattern baldness restricted to the ear results in complete baldness as the dog ages (8 to 9 years). In canine pinnal alope­cia, a small vellus hair usually remains. In both cases the dermatopathologic features are similar: normal epidermis and dermis, hair follicles in any phase of the cycle, normal number but reduced size of hair (both length and diameter).

Treatment is not necessary because the condition is purely cosmetic. If the owner requires a treatment, melatonin or topical minoxidil can be tried; they are not reported to cause any major side effects in dogs.

Periodic Alopecias

Griffin reports a periodic alopecia affecting adult Miniature Poodles. Alopecia of one or both ears is followed by spontaneous hair regrowth within several months.³ The author advises ruling out telogen effluvium, drug reaction, and endocrine diseases. Dermatopathologic features are unknown. No treatment is advised because the condition is purely cosmetic and spontaneously resolves.²⁰

In cats, a spontaneous periodic alopecia restricted to the pinna was described by Scott in Siamese cats. Both ears are affected. The skin is normal, and the alopecia affects the whole pinna or is patchy. Dermatopathologic features are unknown. Spontaneous regression is observed without treatment after several months.

Melanoderma and Alopecia in Yorkshire Terriers

Melanoderma and alopecia are quite common in Yorkshire Terriers and occasionally recognized in other breeds such as the Doberman Pinscher.⁴ The alopecia begins between 6 months to 3 years of age on the bridge of the nose and both pinnae. The tail and feet may also be affected. Affected areas are markedly hyperpigmented (“melanoderma”), alopecic, smooth, and shiny, giving a leathery appearance (“leather ears”).

Diagnosis is based on history, clinical features, and elimination of other diag­noses. Dermatopathologic features are not specific. Carlotti²¹ demonstrated decreased dermal elastin in eight cases and abnormal growth hormone response to clonidine administration.

The disease slowly worsens as the dog ages; spontaneous recovery is rare in the author’s experience.

Figure 12-17

Compared with the rest of the body, pinnal alopecia is moderate in this male Pinscher with testicular tumor and elevated estradiolemia.

Endocrinopathy

Endocrine diseases are the most common cause of noninflammatory primary alope­cia in the dog (Figure 12-17). But in a stereotypic manner, the extremities, including the pinna, are usually spared. In the cat, endocrine diseases usually cause nonspecific cutaneous signs (seborrhea, dull hair coat). Alopecia is a very rare feature of feline endocrinopathy, except for the secondary alopecia associated with the overgrooming behavior observed in some cases of hyperthyroidism.