Discoid lupus erythematosus is an uncommon autoimmune skin disease of dogs. It is considered a benign form of systemic lupus in which the disease is limited to the skin with no systemic signs.

Discoid lupus is aggravated by exposure to UV light and is more common in areas at high altitude with direct sun exposure. The antigens against which the antibodies are directed in discoid lupus are not localized in the skin, but in the immune-complex deposits in the skin leading to cutaneous lesions (type III hypersensitivity).

In addition, it is hypothesized that sunlight may induce the expression of nuclear and cytoplasmic antigens. Specific antibodies are then produced. These antibodies will then bind to the antigen on the surface of the basal cell and this will trigger a cytotoxic process (type II hypersensitivity). The injured keratinocyte will release pro-inflammatory cytokines (interleukin 1, interleukin 6, and tumor necrosis factor alpha) that could be responsible for the accumulation of an inflammatory infiltrate in the area.

Genetics, sunlight and viruses may all be factors involved in the pathogenesis of this disease. Affected animals are otherwise healthy and have no evidence of systemic disease. Discoid lupus does not progress into systemic lupus.

Females are at increased risk for discoid lupus. The disease is confined to the face, and the nose is the most commonly affected area. Collies, German shepherds, Siberian huskies, Shetland sheepdogs and their crosses are predisposed.

Early signs include slate-blue depigmented and erythematosus macules on the planum nasale or on the lips. Loss of the normal cobblestone appearance of the nasal planum is also an early sign of disease. Depigmented lesions rapidly progress to ulcerations and crusting. Scarring may be severe in advanced cases.

Eyelids, lips, pinnae and pads are less commonly affected. Macules evolve into hairless, crusted necrotic lesions. Squamous cell carcinoma has been reported to develop in chronic cases of discoid lupus. This, however, is believed to be quite rare. Disease may run a waxing and waning course and is aggravated by sun exposure. Thus, it may have a seasonal course in some geographical areas.

Related Diseases

Other diseases that have signs of nasal depigmentation and crusting include:

Pemphigus foliaceous

Pemphigus erythematosus

Systemic lupus

Mycosis fungoides

Vogt-Koyanagi-Harada-like syndrome

Dermatomyositis

Erythema multiforme

Contact dermatitis (allergic and irritant)

Nasal solar dermatitis

In areas that are necrotic and ulcerated, vasculitis should be considered. Vasculitis could also be secondary to:

Drugs

Infectious organisms

Autoimmune in origin