Fever of unknown origin (FUO) attributable to indolent lymphoproliferative disorder due to a plasmacytoma expressing immunoglobulin A

Background: The most common categories causing fevers of unknown origin (FUOs) include infective rheumatic/inflammatory disorders and malignancies. Among neoplastic causes of FUOs, lymphomas, hepatomas, renal hypo-nephromas, and hepatomas are the most common. Other malignancies rarely present with FUOs (eg, multiple myeloma). Case Report: We describe a 58-year-old man who presented with an FUO accompanied by night sweats, weight loss, and a groin mass. A biopsy of the groin mass (ie, his lymph node) was negative for infectious diseases, rheumatic or inflammatory diseases, and malignancies. Histochemical and immunological studies of the lymph node showed it to contain a plasmacytoma expressing immunoglobulin A (IgA). An immunohistochemical study of the plasma-cell infiltrate demonstrated strong CD138 staining. A bone marrow biopsy was negative for multiple myeloma. Conclusion: We believe this is the first reported rare case of an indolent, lymphoproliferative disorder attributable to an IgA-secreting plasmacytoma presenting as an FUO.