Histopathology of the lepromatous skin biopsy

The histopathology of lepromatous skin varies according to the cell-mediated immunity of the host against Mycobacterium leprae. In tuberculoid and borderline tuberculoid leprosy, epithelioid noncaseating granulomas predominate, and acid-fast bacilli (AFB) are absent or only rarely present. In borderline lepromatous and lepromatous leprosy, the infiltrate is composed of macrophages with a vacuolar cytoplasm, lymphocytes, and plasma cells. AFB are numerous. Edema inside and outside the epithelioid granulomas, together with the appearance of large giant cells, are the main features of type 1 reactions. A conspicuous neutrophilic infiltrate in the subcutis with or without vasculitis is found in erythema nodosum leprosum. The main histopathologic features of leprosy and its particular forms are discussed in this review.