Adult pulmonary Langerhans' cell histiocytosis.

Adult pulmonary Langerhans' cell histiocytosis is a rare disorder of unknown aetiology that occurs predominantly in young smokers, with an incidence peak at 20-40 yrs of age. In adults, pulmonary involvement with Langerhans' cell histiocytosis usually occurs as a single-system disease and is characterised by focal Langerhans' cell granulomas infiltrating and destroying distal bronchioles. High-resolution computed tomography (HRCT) of the chest is essential to the diagnosis, typically showing a combination of nodules, cavitated nodules, and thick- and thin-walled cysts. A high macrophage count in bronchoalveolar lavage (BAL) fluid is a common but nonspecific finding that merely reflects exposure to tobacco smoke. BAL is useful for eliminating infections and the other infiltrating lung disorders that can be seen in young adults. Langerhans' cells can be identified in BAL fluid, but, in contrast to what was initially hoped, this test shows a very low sensitivity and is rarely useful in the diagnosis of the disease. The definite diagnosis of pulmonary Langerhans' cell histiocytosis requires identification of Langerhans' cell granulomas, which is usually achieved by surgical lung biopsy at a site selected by chest HRCT. In practice, however, lung biopsy is performed on a case-by-case basis. No effective treatment is available to date, and improved understanding of the mechanisms involved in the pathogenesis of pulmonary Langerhans' cell histiocytosis is urgently needed, and should help in the development of specific therapeutic strategies for patients with this orphan disease.