[Histopathological aspects of Langerhans cell histiocytosis. With emphasis on the pulmonary form].

Langerhans cell histiocytosis (LCH) occurs principally but not exclusively in younger age groups. It can present as a single lesion or as multiple lesions and can affect one or several organ systems. Diagnosis of LCH requires the identification of CD1a and S-100 positive histiocytes. The range of synonyms used for LCH reflects both the variable clinical presentation and the variations in the histological "development stage" of the individual lesions from one case to another. The term LCH has now been accepted for all manifestations of the disease. The extent of the disease in a given case is specified by determining the number and location of foci and by ascertaining whether one or several organ systems are affected, and whether organ dysfunction exists. Among cases of LCH in adults, pulmonary LCH has a special status, as this usually results from cigarette smoking and is generally limited to the lungs. The lungs may also be affected in "conventional" LCH, and organ dysfunction may also exist in this form of the disease. In general, the morphology of LCH is sufficiently characteristic that the differential diagnosis versus other types of histiocytosis should not be difficult, provided an adequate specimen is available for examination.