Pulmonary Langerhans' cell histiocytosis in adults.

Pulmonary Langerhans' cell histiocytosis (PLCH) is a rare disorder of unknown cause characterised by the infiltration of the lungs and other organs by the bone marrow derived Langerhans' cells, which carry mutations of BRAF gene and/or NRAS, KRAS and MAP2K1 genes. It occurs predominantly in young smokers, without gender predominance. The disease is characterised by formation of eosinophilic granulomas with the presence of Langerhans' cells infiltrating and destroying distal airways. High-resolution computed tomography of the chest (HRCT) plays an outstanding role in PLCH diagnosis. The typical radiological picture of PLCH is the presence of small intralobular nodules, often forming 'tree in bud' lesions, cavitated nodules, thin- and thick-walled cystic lesions frequently confluent. Definite diagnosis requires the finding of characteristic lesions in histological examination and demonstration of antigen CD1a or CD207 presenting cells in immunohistochemistry. Smoking cessation is the most important recommendation for PLCH patients. There are no evidence based data regarding systemic steroid therapy. The treatment of progressive PLCH is based on cladribine or cytarabine as salvage therapy. The prognosis is good, and over 85% of patients survive 10 years.