Langerhans cell histiocytosis--clinical and epidemiological aspects.

Langerhans cell histiocytosis is a disease which frustrates both clinician and scientist. Its aetiology is unknown, its pathogenesis is ill understood and the clinical course is unpredictable. Historically, the different nomenclatures reflecting the first clinical descriptions by Hand (1893, 1921), Schuller (1915) and Christian (1920), and subsequently by Letterer (1924) and Siwe (1933), led to confusion only partially resolved by Lichtenstein (1953) who recognised that the disease in each of these clinical syndromes were components of a spectrum of disease involving the histiocyte. He proposed his unifying concept of Histiocytosis X--'X' being the unknown aetiological factor. In 1973, Nezelof recognised the lesional cell as a 'Langerhans-like' cell but it took another decade for the disease to be recognised as a single entity and the term Langerhans cell histiocytosis to be internationally accepted. The publication, by the Histiocyte Society (1987), of their classification of the histiocyte disorders together with criteria for pathological diagnosis and clinical evaluation of Langerhans cell histiocytosis have consolidated the position. This article details the wide variety of clinical manifestations of the disease and its sequelae and discusses possible epidemiological factors. Finally it looks at the potential implications of recent scientific research on the management of the disease.