By Gary M. White, MD
Lupus vulgaris is infection of the skin by Mycobacterium tuberculosis in a person with moderate to high immunity.
The typical clinical presentation is that of a plaque on the face or elsewhere that slowly enlarges over time. The buttocks, legs and feet are most commonly affected. It may be crusted, verrucous, hyperkeratotic, annular or granulomatous. Diascopy reveals the typical apple jelly color.
Diascopy is the procedure of pressing a glass slide over a skin lesion in order to examine it with the blood squeezed out blood. It may be done with hemangiomas or other vascular lesions to confirm the diagnosis (the lesion disappears) or for lupus vulgaris to view a yellowish brown shade of color that is reminiscent of apple jelly. It is thought to represent the collection of tubercles in the dermis with degenerative changes. Although highly characteristic of lupus vulgaris, it is not pathognomonic as other chronic granulomatous disorders of skin such as lupoid leishmaniasis, sarcoidosis, lupoid rosasea, granuloma facial and pseudolymphoma may also give similar appearance on diascopy.
If the diagnosis is suspected, workup should include skin biopsy, CXR and PPD.
The latest antituberculous treatment recommendations should be consulted.
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