A case of invasive Langerhans cell histiocytosis localizing only in the lung and diagnosed as pneumothorax in an adolescent female.

In infants, Langerhans cell histiocytosis (LCH) is associated with poor clinical outcomes as Langerhans cells invade and damage multiple organs, a presentation that is different from that in adults. Here, we present a case of a 15-year-old female who visited ourclinic complaining of right chest pain and dyspnea. She was diagnosed with right pneumothorax by chest X-ray. Chest computed tomography showed multiple cystic changes in the bilateral lung. Additionally, bullous lesions occupying the upper lobe and multiple white tiny nodules on the surface of the lung were observed by thoracoscopy. These nodules comprised proliferating atypical CD1a/S-100-positive cells invading the pulmonary parenchyma, leading to the diagnosis of LCH. Because of the extensive invasion into the pulmonary parenchyma, chemotherapy was administered. This case of LCH was unique in that the age of onset was atypical and the tumor cells occupied a single organ, despite their malignant behavior.