Primary plasmacytoma involving mediastinal lymph nodes: A diagnostic mimicry of primary mediastinal lymphoma

Plasmacytomas could involve any organ, and at times might pose a diagnostic challenge when the site of involvement is unusual, or if the presentation is similar to other diseases. We describe a 48-year-old man presenting with worsening shortness of breath and chest discomfort with radiologic evidence of mediastinal enlargement, mimicking a lymphoma with mediastinal involvement. An excisional biopsy of a mediastinal lymph node showed a plasma-cell infiltrate strongly positive for CD138, with a flow-cytometry analysis showing a population of lambda-restricted neoplastic plasma cells. He failed to respond to 50 Gy involved-field radiotherapy, but achieved a partial response to combination chemotherapy. He underwent high-dose chemotherapy with melphalan (200 mg/m²) followed by lenalidomide maintenance, and is in complete remission 18 months postautografting. This case illustrates a unique and rare presentation of primary lymph-node plasmacytomas involving the mediastinum potentially mistaken as lymphoid malignancy. Clinicians should be aware of the plasma-cell origin of the mediastinal neoplastic process.