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INCIDENCE Although the incidence of lupus vulgaris has steadily declined during the past decades, it was estimated in 1960 that some 50,000 new cases occur throughout the world every year. It has always been less common in the United States than in Europe. Females appear to be affected two to three times as often as males; all age groups are affected equally.

PATHOGENESIS Lupus vulgaris is a postprimary, paucibacillary form of skin tuberculosis arising in previously sensitized individuals with only moderate immunity. It originates by hematogenous, lymphatic, or contiguous spread from tuberculosis elsewhere in the body, most often from cervical adenitis or pulmonary tuberculosis, but sometimes from an old, apparently quiescent primary complex. Rarely, it follows primary inoculation tuberculosis or BCG vaccination 13 (see below). The lesions progress steadily. Spontaneous involution may occur and new lesions may arise within old scars. Complete healing occurs only rarely without therapy.

CLINICAL MANIFESTATIONS The lesions are usually solitary, but two or more sites may be involved simultaneously; in patients with active pulmonary tuberculosis, multiple foci may develop. In approximately 90 percent of patients, the head and neck are involved. Lupus vulgaris usually starts on the nose or cheek and slowly extends onto adjacent areas. The earlobes are often affected, and solitary patches may be encountered on the scalp. Only a small percentage of the lesions occur on the extremities, and, except for patients with disseminated lupus vulgaris, the trunk is rarely involved. In general, lupus vulgaris is asymptomatic. The initial lesion is a brownish-red, soft or friable lupus macule or papule with a smooth surface or covered by a scale. On diascopy the infiltrate exhibits a typical apple-jelly color. Progression is characterized by elevation, a deeper brownish color, and formation of a plaque. Involution in one area and simultaneous expansion in another result in a gyrate outline.

Lesions may become flat plaques with a serpiginous or polycyclic outline and a smooth surface or psoriasiform scaling; there may be erosions, ulceration, and scarring. Hypertrophic forms appear as a soft mass with a nodular, hyperkeratotic surface. Edema, lymphatic stasis, recurrent erysipelas, elephantiasic thickening, and vascular dilatation may lead to gross deformity. In ulcerative forms, the underlying tissue may be affected by progressive necrosis; involvement of the nasal or auricular cartilage results in extensive destruction and disfigurement.

Atrophic scarring, with or without prior ulceration, is a prominent feature of lupus vulgaris. Recurrence within a scar is characteristic. Sometimes, fibrosis is very pronounced and leads to deformations, mutilations, and contractures.
Lupus vulgaris of mucous membranes The mucosae may be primarily involved or become affected by the extension of skin lesions. They show small, soft, gray or pink papules, ulcers, or granulating masses that bleed easily. A dry rhinitis is often the only symptom of early nasal lupus, but progressive lesions destroy the cartilage of the nasal septum. Scarring of the soft palate and stenosis of the larynx may also result.
Lupus postexanthematicus After a transient impairment of immunity, particularly after measles (thus the term lupus postexanthematicus), multiple disseminated lesions may arise simultaneously in different regions of the body as a consequence of hematogenous spread from a latent tuberculous focus. During and after the eruption, a previously positive tuberculin test may become negative but will usually revert to positive as the general condition of the patient improves. Clinically and histopathologically, the lesions of postexanthematic lupus are typical for lupus vulgaris, and their appearance distinguishes the condition from acute miliary tuberculosis of the skin.

DIAGNOSIS AND DIFFERENTIAL DIAGNOSIS Typical lupus vulgaris plaques do not present diagnostic problems; they have to be distinguished from lesions of sarcoidosis, lymphocytoma, discoid lupus erythematosus, tertiary syphilis, leprosy, blastomycosis or other deep mycotic infections, lupoid leishmaniasis, and chronic vegetating pyodermas. Criteria helpful in the diagnosis are the softness of the lesions, the brownish-red color, and the slow evolution. The apple-jelly nodules revealed by diascopy are highly characteristic; finding them may be decisive, especially in ulcerated, crusted, or hyperkeratotic lesions. Histologic examination and a positive culture for M. tuberculosis/bovis confirm the diagnosis. The tuberculin test is strongly positive except for the early phases of postexanthematic lupus.