Congenital Anomalies of the Skin in Animals

Congenital dermatoses of the skin may be genetic or arise during embryogenesis because of nongenetic factors. Genetic mutations that cause skin anomalies may be present at birth or become apparent weeks to months later. These late-onset manifestations are referred to as tardive developmental defects.

Both congenital and tardive developmental dermatoses are fairly common in all species of domestic animals, with the greatest number of well-defined defects described in cattle and dogs. Skin is of ectodermal origin and therefore often associated with other ectodermal defects (eg, dentition).

Epitheliogenesis imperfecta (aplasia cutis) is a congenital discontinuity of squamous epithelium that occurs in cattle (autosomal recessive trait), horses, and swine, and rarely in sheep, cats, and dogs.

In cattle, affected breeds include Holstein-Friesian, Hereford, Ayrshire, Jersey, Shorthorn, Angus, Dutch Black Pied, Swedish Red Pied, and German Yellow Pied.

Epitheliogenesis imperfecta is common in swine, in which large lesions are obvious at birth as glistening, red, well-demarcated discontinuities in skin or mucous membranes (see epitheliogenesis imperfecta image). Infection and ulceration are early consequences. One or more hooves or claws may be deformed or absent; other associated congenital anomalies appear in some affected animals. The condition is fatal when extensive; however, small defects can be surgically corrected.

Epitheliogenesis imperfecta, pig

Image

Courtesy of Dr. Aiden Foster.

Ultrastructural evaluation of this condition in American Saddlebred foals has demonstrated a relationship with junctional epidermolysis bullosa.

Focal cutaneous hypoplasia and subcutaneous hypoplasia are congenital, circumscribed hypoplastic defects of multiple or deeper skin layers in swine. Lesions manifest as skin depressions in which all skin layers or only the subcutaneous fat layers fail to develop normally.

A nevus is a circumscribed developmental defect of the skin, whereas a hamartoma is a hyperplastic mass formed as a result of a developmental defect in any organ. Both nevi and hamartomas have been described as congenital skin defects; however, the problem may not become obvious until later in life. In dogs, sebaceous nevi, pigmented epidermal nevi, inflammatory linear verrucous epidermal nevi, nevi comedonicus, linear organoid nevi, and follicular hamartomas are known to occur. In horses, cannon keratosis and linear epidermal nevi have been described. Similar defects doubtless occur in all species.

Mixed, or organoid, nevi consist of circumscribed collections of densely packed adnexal structures (eg, pilosebaceous nevus). Collagenous nevi are nodules composed of focal collagen hyperplasia that displace normal skin structures. Most lesions are alopecic, with pigmented, pitted surfaces. When not extensive, nevi can be excised; otherwise, no effective treatment is known.

Dermoid sinuses or cysts (gene variants fgf3, fgf4, fgf19) occur in Thoroughbred horses and Rhodesian Ridgebacks (in which they are inherited) and occasionally in other dog breeds. These cystic structures are lined with skin in which exfoliated skin, hair, and glandular debris accumulate (see dermoid sinus images). They are caused by failure of the neural tube to completely separate from the epidermis during embryogenesis. Cysts are found on dorsal midline and are rarely associated with spinal cord neural deficits. They can be surgically excised.

Dermoid sinus, dog

Image

Courtesy of Dr. Jamie Textor.

Follicular cysts are common clinical findings that develop by abnormal hair follicle morphogenesis and retention of follicular or glandular products. They may be congenital when the follicular orifice fails to develop normally. Congenital cysts are most commonly identified in Merino and Suffolk sheep. Periauricular (dentigerous) cysts occur in horses and, although present at birth, may not be recognized until adulthood. Wattle cysts arise from the branchial cleft in Nubian goats. Porcine wattles, teatlike growths on the lower jaw, occur fairly frequently in all swine breeds.