A case of interface perianal dermatitis in a dog: is this an unusual manifestation of lupus erythematosus?

Discoid lupus erythematosus (DLE) is a well-known autoimmune disorder described in dogs and humans. In dogs, DLE is considered the second most common immune-mediated dermatitis and is usually localized to the nasal planum. DLE does not evolve to generalized disease, however lesions may spread to the bridge of the nose and less commonly may extend to periocular region, pinnae, distal limbs, and mucocutaneous junctions (lips, oral cavity, and genital region). A 4-year-old male Bavarian Mountain Scenthound developed a chronic, erosive, cutaneous lesion located exclusively in the perianal region without facial skin involvement. Clinical signs included erythema, depigmentation, severe alopecia, crusting, and ulceration. Histologically, the hallmarks of the changes were an interface dermatitis consisting of plasma cells, lymphocytes, neutrophils, and macrophages, hydropic degeneration of basal cells, few apoptotic cells in the basal layer, pigmentary incontinence, and a focal thickening of the basement membrane, which was characterized by linear deposition of IgG. Despite the unusual localization the lesion was diagnosed as DLE based on the characteristic histologic and immunohistologic features. Following diagnosis, corticosteroid therapy resulted in a complete resolution of perianal lesions.