[Pulmonary manifestations of Langerhans cell histiocytosis]

Pulmonary Langerhans cell histiocytosis is a rare diffuse cystic interstitial pneumonia of unknown etiology that occurs selectively in young smokers of both genders. The multicenter studies conducted by the reference center have better defined the short and medium terms natural history of the disease and the clinical management of patients. A substantial proportion of patients experience a dramatic decline in their lung function soon after diagnosis. Importantly, smoking cessation is associated with a decreased risk of subsequent deterioration. Cladribine, a purine analogue, chemotherapy may dramatically improve lung function in patients with progressive pulmonary Langerhans cell histiocytosis, but this treatment should be used only in the setting of clinical research. Specific pulmonary hypertension therapies (anti-endothelin receptors, inhibitors of phosphodiesterases) may be used with caution in specialized centres for patients with severe pulmonary hypertension, and seem to be well tolerated. The recent identification of the V600E mutation of the BRAF oncogene in approximately half of the Langerhans cell histiocytosis lesions, including pulmonary granulomas, represents an important step forward in the understanding of the pathogenesis of Langerhans cell histiocytosis. Potentially it opens the way to targeted therapies.