Lucio's phenomenon/erythema necroticans.

Lucio's phenomenon/erythema necroticans is a peculiar reaction pattern that occurs in untreated pure primitive diffuse lepromatous leprosy (PPDL) and/or relapsing leprosy recognized as spotted leprosy of Lucio. The small number of reported cases in the world literature suggests that it is fairly uncommon. Its clinical features are fairly characteristic and consist of extensive, bizarre, painful ulcerations of the skin, with constitutional symptoms being conspicuous by their absence. The clinical diagnosis is confirmed by microscopic pathology marked by proliferation and mobilization of polyblasts and histiocytes, dilatation, endothelial proliferation, luminal occlusion, and thrombosis of the superficial and mid-dermal blood vessels and demonstration of acid-fast bacilli in the blood vessel walls. Its precise pathogenesis is still unclear, but is believed to occur either through the usual or the alternate pathway of complement activation in the natural history of erythema nodosum leprosum. The clinical and immunological features of reactions in leprosy, including erythema nodosum leprosum, are well known and have been critically evaluated elsewhere.