Pulmonary Langerhans cell histiocytosis (PLCH) is a rare interstitial lung disease (ILD) that is strongly associated with smoking and primarily affects adults. In its early stages, the disease is characterized by bronchiolocentric nodules with infiltration of Langerhans cells (CD1a-positive on immunostaining), often accompanied by eosinophils and chronic inflammatory cells, and may include cavity formation. In later stages, Langerhans cells may become less prominent, and stellate fibrotic lesions typically develop.
PLCH has an insidious onset, presenting with symptoms such as cough and dyspnea. In approximately 1/4 of cases, it is incidentally detected on chest imaging, while some patients are diagnosed after presenting with pneumothorax.
Chest X-rays typically show nodular or reticulonodular infiltrative lesions, predominantly in the upper and middle lung zones, with clear costophrenic angles. High-resolution computed tomography (HRCT) characteristically reveals multiple irregular cysts of varying sizes and wall thicknesses, often accompanied by peribronchiolar nodules (1-4 mm in diameter) in the early stages. These findings are primarily distributed in the upper and middle lung fields. The presence of multiple cysts and nodules predominantly in the upper and middle lung zones, along with a bronchoalveolar lavage fluid (BALF) Langerhans cell count exceeding 5%, strongly suggests the diagnosis of PLCH.
The primary treatment is smoking cessation, which is crucial for disease management. For patients with severe disease or those who experience progressive symptoms despite quitting smoking, glucocorticoid therapy may be required.