Pulmonary histiocytosis X with mediastinal lymph node involvement.

In this report, we describe a patient with the classic histology of pulmonary histiocytosis X, who had bilateral reticulonodular densities and mediastinal lymph node involvement. The diagnosis was confirmed by the use of electron microscopy and immunohistochemical markers (PS100, HLA-DR, and CD1), which allowed us to recognize the lymph node infiltration of X histiocytes. An association of mediastinal lymph node enlargement with pulmonary histiocytosis X has been reported but it has never been histologically documented.