Histopathology of the Skin

Abstract

Leprosy histopathology is characterized by granulomatous infiltrate with only few exceptions (indeterminate leprosy and some particular forms). The clinical spectrum of the disease has its direct correlate on histopathology, reflecting the different grades of cell-mediated immune response. The tuberculoid pole is characterized by multifocal epithelioid granulomas with giant cells, neural involvement, and no or very few bacilli, while the lepromatous pole is characterized by macrophage infiltrate without true granuloma formation and presence of foamy cells (Virchow cells) with many bacilli. Perivascular and periadnexal and/or perineural lymphohistiocytic infiltrate is found in indeterminate leprosy. Dermal edema, intragranuloma edema, and giant cell size are typical features of type 1 reaction, while edema in the dermis and neutrophilic infiltrate with background changes of pre-existing lepromatous lesions are the diagnostic clues for erythema nodosum leprosum. Final diagnosis can be based only on accurate clinico-bacteriological-pathologic correlation.