A ten year-old girl presented with increased susceptibility to infection, massive enlargement of the cervical lymph nodes, a high erythrocyte sedimentation rate and an extremely high serum IgA (peak level 66 g/l). The diagnosis of plasmacytoma was confirmed by the identification of a monoclonal immunoglobulin (IgAk) in the serum and in the plasma cells present in a cervical lymph node biopsy. Her disturbed blood coagulation and thrombelastogram, serum hyperviscosity, cryoglobulinemia, hyponatremia and constantly positive test for rheumatoid factor without evidence of rheumatic disease were attributed to the effects of the myeloma proteins. Other signs often associated with plasmacytoma (bone pain, osteolytic lesions, anemia, bone marrow failure or infiltration) were absent indicating that the plasmacytoma originated in a lymph node, which is unusual. This case is the second well-documented childhood plasmacytoma to be reported. With combined melphalan and prednisone therapy, the greatly enlarged lymph nodes regressed in size and the plasma IgA concentration fell to normal. Immunological investigations revealed a considerable reduction of blood T cells, and abnormal skin tests at the time of diagnosis indicated a disturbance of cellular immunity. There were also abnormalities in the B-cell system. The blood B lymphocytes were found to carry only complement receptors for C3b and mainly for IgA, whereas in normal individuals blood B cells bear complement receptors for both C3b and C3d and mainly surface Ig of the IgM class. In the lymph node biopsy, there were many primary follicles expressing complement receptors for both C3b and C3d among the dense plasma cell infiltrates, but germinal centers, which mainly serve to renew B cells, were completely absent. In conjunction with data from the literature, we concluded 1) that the production of normal B lymphocytes is blocked, probably due to a secondary T cell deficiency, and 2) that the majority of the residual blood and bone marrow B cells and the plasmacytoma cells are parts of the same neoplastic cell clone.
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