[A case of extramedullary plasmacytoma in the mediastinum]

A 80-year-old man was admitted to our hospital for examination of a mediastinal mass. Chest CT showed a 6 x 9 cm mass in the left anterior mediastinum. The left main bronchus and pulmonary artery were invaded by the mass. Bronchoscopic examination showed compression of the left main bronchus by the mass and enlarged lymph nodes. The left upper lobe and lingular bronchi were almost occluded. The overlying mucosa was invaded by tumor tissue. Microscopic findings of specimen obtained by transtracheal biopsy showed plasma cells of various sizes were at different stages of differentiation. Immunohistochemical staining revealed IgA monoclonality. Whole-body bone scan and bone marrow aspiration excluded multiple myeloma and a diagnosis of extramedullary plasmacytoma was made. Serum protein electrophoresis showed an IgA monoclonal gammopathy. Immunoelectrophoresis of the serum revealed an IgA kappa monoclonal component. These suggested that tumor cells were producing monoclomal IgA kappa light chain. Radiotherapy was effective in reducing the size of the plasmacytoma, and serum IgA reverted to normal. A 67-Ga scan showed strongly increased uptake in the left anterior mediastinum. Chest CT after radiotherapy showed that the decreased mass had an extrapleural sign against the mediastinal pleura. We determined that the origin of the plasmacytoma was probably the mediastinum. We reported a rare case of extramedullary plasmacytoma in the mediastinum.