[Histiocytosis syndrome in children].

The recommended classification of the histiocytosis syndromes in children is as follows: 1. Langerhans' cell histiocytoses. 2. histiocytoses of mononuclear phagocytes. 3. neoplastic histiocytoses. The previous term, histiocytosis X, including eosinophilic granuloma of bone, the Hand-Schüller-Christian syndrome and Letterer-Siwe's disease, is now more correctly called Langerhans' cell histiocytosis (LCH) since the infiltrating cell in histiocytosis X both histologically and immunophenotypically is identified as the Langerhans' cell. Local and generalized LCH differmarkedly with respect to treatment and outcome. It is therefore necessary to perform an extensive investigation at the time of the initial evaluation of the patient. The most common mononuclear phagocytic syndromes are the familial erythrophagocytic lymphohistiocytosis and infection-associated or reactive hemophagocytic syndromes. The pathognomonic cell in familial erythrophagocytic lymphohistiocytosis is possibly a hybrid phenotype sharing characteristics of the two main types the mononuclear phagocyte system - i.e. the Langerhans' cells and phagocytic macrophages. Malignant histiocytosis is rarely seen in children and is a form of the Ki-1 positive anaplastic cell lymphoma.