[Pneumothorax secondary to pulmonary histiocytosis X]

The authors report a case of pneumothorax in a young man suffering from pulmonary histiocytosis. They take this observation as a starting point for discussing about the so-called "histiocytosis X". The term "histiocytosis" is a term for a variety of proliferative disorders of histiocytes or macrophages. There is a small cluster of conditions characterized by proliferation of a special type of histiocyte called the "Langerhans' cell". The proliferation of Langerhans' cells results from disturbances in immunoregulation. Particularly, there are three clinicopathologic entities: *Letterer-Siwe disease (acute disseminated Langerhans' cells histiocytosis), *multifocal eosinophilic granuloma or Hand-Schüller-Christian disease (multifocal Langerhans' cells histiocytosis), *unifocal eosinophilic granuloma (unifocal Langerhans' cells histiocytosis). In the past, these were collected in the not specific term of histiocytosis X. Most patients with Langerhans' cell granulomatosis have diseases limited to the lung, only a small proportion have extrapulmonary involvement or a systemic disorder. Typically, there are expanding, erosive accumulations of Langerhans' cells within the medullary cavities of bones. In this reported case, a patient, two years before, was affected by osteolytic bone lesion in the left femur. Pulmonary histiocytosis is often seen in smokers in the third and fourth decade of life. The 20% of patients are asymptomatic and found to have an abnormal chest radiograph; a lesser proportion presents with pneumothorax. Some patients develop progressive fibrotic lung disease and respiratory failure. Chest radiographs may show bilateral reticular or reticulonodular infiltrates, sometimes with cystic changes, often with sparing of the costophrenic angles, but high resolution computerized tomography scans may be virtually diagnostic based on the predilection of the cysts and nodules for the upper lung zones. Sometimes the typical Langerhans' cells may be recovered in bronchoalveolar lavage fluid of patients with active disease. The combination of the characteristic CT findings and Langerhans' cells in bronchoalveolar lavage fluid should be diagnostic, decreasing the number of cases requiring for diagnosis open lung biopsy. The differential diagnosis is with sarcoidosis, tbc, diffuse metastases, lymphoma, eosinophilic pneumonia, fibrosing interstitial pneumonia.