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 les ions and can affect one or several organ systems. Diagnosis of LCH requires the identification of CD1a and S-100 positive histiocytes. The range of sy nonyms used for LCH reflects both the variable clinical presentation and th e variations in the histological "development stage" of the individual lesi ons from one case to another. The term LCH has now been accepted for all ma nifestations of the disease. The extent of the disease in a given case is s pecified by determining the number and location of foci and by ascertaining whether one or several organ systems are affected, and whether organ dysfu nction exists. Among cases of LCH in adults, pulmonary LCH has a special st atus, as this usually results from cigarette smoking and is generally limit ed 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,th e morphology of LCH is sufficiently characteristic that the differential di agnosis versus other types of histiocytosis should not be difficult, provid ed an adequate specimen is available for examination.