Histiocytoses

Abstract

Histiocytoses are classified into two main groups according to the morphologic and immunophenotypic characteristics of the cells forming the infiltrate: Langerhans cell histiocytoses, which are formed by a very precise type of cells harboring Birbeck granules and expressing antigens like CD1a, langerin; and the non-Langerhans cell histiocytoses, in which cells of monocyte/macrophage or dendritic lineage proliferate. A clear distinction between these two groups of cells was lacking in the past. However, in the last decades it is well known that both groups of diseases have different histopathologic, immunophenotypical, and electron microscopic findings and systemic manifestations. Among the various diseases classified in the group of non-Langerhans cell histiocytoses, histopathology and immunophenotyping are sometimes not sufficient to make a precise diagnosis. Clinical features including extent, and type of the skin lesions and associated systemic findings may be crucial in establishing the proper diagnosis.