Histiocytoses.

Childhood histiocytoses are a rare and diverse group of histiocytic disorders. This review will focus on clinical, pathological and immunopathological features of these syndromes. The pathogenesis of Langerhans' cell histiocytosis or class I histiocytosis, a proliferative disorder of the Langerhans' cell, remains enigmatic. Approaches to treatment are as varied as the clinical presentations, ranging from a fatal leukaemia-like disorder to solitary lytic lesions of bone. Recent findings indicate that Langerhans' cell histiocytosis is a clonal histiocytic disease. The two major class II histiocytoses are familial erythrophagocytic lymphohistiocytosis and the reactive haemophagocytic syndromes. The clinicopathological similarities between these two entities suggest that they share a common immunological feature in which uncontrolled cytokine release from activated T-cells leads macrophages to a haemophagocytosing state.