The patient was a 35-year-old man who was referred to the clinic for evaluation of a radiological alteration of the chest. He had no drug allergies, he was allergic to pollen. He worked as a plasterboard worker. He had smoked 10 cigarettes/day since the age of 14 (10.5 packs/year) and 8 joints of marijuana/day. He consumed alcohol occasionally. He had no family history of interest. During the last year, he reported coughing predominantly in the evening and at night when lying on his back, accompanied by white expectoration. He also had associated wheezing that improved with bronchodilators. He also reported dyspnoea on exertion. He had lost about 5 kg in weight. She reported asthenia which she related to work. She had a dog at home. He had not travelled recently nor had he had any known contact with tuberculosis patients.
On physical examination he was in good general condition, eupneic with a baseline oxygen saturation of 98%. There were no adenopathies or acropacities. Cardiopulmonary auscultation was normal.
Chest X-ray (CXR) showed a diffuse linear interstitial pattern predominantly on the right. The study was completed with several complementary explorations: blood tests with all parameters within normality, including autoimmunity and negative serology, respiratory function tests (RFT) within normality, negative Mantoux, computed tomography (CT) of the chest showing the lung parenchyma occupied by multiple small cavitary-cystic lesions, widely distributed in both lung fields, with involvement of both upper and lower fields.

Based on these findings, bronchoscopy was performed and no mucosal alterations or lesions were observed. Three BAL scans were performed in the right upper lobe, which were sent for cytology, smear microscopy and lymphocyte subpopulations. In addition, four bronchoaspirate secretions (BAS) were performed for fungi, Pneumocystis, culture and Koch's bacillus. All results were negative. The bronchoaspirate pathology report revealed minimal inflammatory component, with no abnormal histiocytes or atypical cells. Immunohistochemistry was negative for S100 and CD1a.
Given this result, a biopsy of the right upper lung lobe was performed by thoracotomy. Pathology was compatible with Langerhans' histiocytosis in the proliferative or cellular phase.
The patient was advised to stop smoking. He was seen 3 months later and reported being asymptomatic with a gain of 6 kg. However, in the control chest X-ray the interstitial pattern remained.