[Langerhans-cell histiocytosis (histiocytosis X) in children]

Langerhans cell histiocytosis (LCH), formerly histiocytosis X, is a rare disorder of unknown aetiology and pathogenesis which is characterized by clinical heterogeneity and an unpredictable course. LCH is considered to be a reactive, proliferative disease. The pathognomonic cell in the lesion has been shown to be identical or very similar to the Langerhans cell. Immunophenotyping studies have shown the cell to be CD1a (OKT-6), S-100 protein, HLA-DR, and CD4 positive; ultrastructurally, the presence of intracytoplasmic Birbeck granules is the hallmark of the entity. The lesions may be localized or generalized. Due to the lack of an accepted classification system for the stage of the disease and its rarity, very few comparative therapy studies have been carried out. Recently, the Histiocyte Society has suggested diagnostic criteria for LCH, and established a program of initial evaluation of the patient in order to start controlled treatment trials. Traditionally, chemotherapy has been preferred with a trend over time towards a more conservative approach. The rate of sequelae is high and connected to a chronic course of recurrent multiosseous disease. Case fatality is strongly associated to development of organ dysfunction seen in disseminated disease, which is especially seen at low age (< 2 years) of onset.