53 Cutaneous lupus erythematosus
Although discoid (cutaneous) lupus erythematosus is uncommon, it is still the most frequently encountered immune-mediated disease in general practice. Generally, the lesions are confined to the bridge of the nose and the nasal planum; however, they can occur on feet and other mucocutaneous sites, such as the genitalia and anal mucosa. The condition is aggravated by sunlight. There has been some discussion on the use of the term ‘discoid lupus erythematosus’, as the clinical presentation is different from that seen in humans and the histology of the condition is not lupus specific (it is also commonly seen in mucocutaneous pyoderma). It has been suggested that the term cutaneous lupus erythematosus may be more appropriate. This case report describes the condition on the nasal planum and the feet of a dog and is referred to as cutaneous lupus erythematosus.
Generally, lesions are first noted on the nose and less frequently other sites may become involved. An astute owner may also be aware of a seasonal exacerbation of the clinical signs. The duration of the condition varies between individuals, and it may wax and wane over several weeks or months. Pruritus is variable.
Most frequently, lesions will be distributed on the bridge of the nose and the nasal planum. Erythema, ulceration, crusting, scaling and alopecia are the most common signs on the bridge of the nose. The nasal planum usually loses its cobblestone appearance, becoming smooth with depigmentation, crusting and ulceration. In rare cases, the condition may involve other sites, such as the ears, lip margins, periorbital areas, pinnae, genital areas and the feet.
Given the previous history and histopathology results, cutaneous lupus erythematosus was still the most likely diagnosis despite the previous poor response to treatment. However, it is possible that a secondary infection was masking some other differential, or that the biopsy samples might have been obtained from inappropriate sites.