Lab Med Online.  2011 Jul;1(3):158-162.

Immunoglobulin Isotype Switching in a Plasma Cell Myeloma Patient Treated with High-dose Chemotherapy and Hematopoietic Stem Cell Transplantation

• Ham JY
• Lee KM
• Song KE

Abstract

A malignant plasma cell clone usually produces a single abnormal monoclonal protein with a constant isotype. However, switching of paraprotein isotype has been reported to be a transient phenomenon associated with the recovery of B-cell function, and, in some cases, the switching might be misinterpreted as relapse. In August 2008, we encountered a case of a 59-year-old man with proteinuria and high IgG level (5.6 g/dL), kappa free light chain level of 2,660 mg/L, reversed A/G ratio (0.51), and multiple osteolytic lesions. Plasma cells, which accounted for 57% of all the nucleated cells, in bone marrow aspirates were positive for kappa immunostaining. Serum protein electrophoresis showed one M-spike, concentration of 4.87 g/dL in the beta region. Immunofixation electrophoresis revealed the peak as an IgG-kappa monoclonal protein; therefore, a diagnosis of plasma cell myeloma was made. Complete remission was achieved after chemotherapy, and autologous peripheral stem cell collection was performed. In March 2009, the patient underwent high-dose chemotherapy and autologous peripheral stem cell transplantation support. After 2 months, serum protein electrophoresis showed 2 M-spikes in the gamma region with positive IgM-lambda, IgG-lambda, and IgG-kappa, and these bands persisted. The electrophoretic mobility of the IgG-kappa protein was different from that of the original disease protein, and bone marrow results were the same as the previous ones. Although immunoglobulin isotype switch is known to have a benign course, it always requires careful monitoring because, in rare cases, true clonal switching may occur.

Keyword

Plasma cell myeloma; Immunoglobulin isotype switching; Hematopoietic stem cell transplantation

MeSH Terms

B-Lymphocytes
Bone Marrow
Clone Cells
Electrophoresis
Hematopoietic Stem Cell Transplantation
Hematopoietic Stem Cells
Humans
Immunoglobulin Class Switching
Immunoglobulin G
Immunoglobulins
Light
Middle Aged
Multiple Myeloma
Peripheral Blood Stem Cell Transplantation
Plasma
Plasma Cells
Proteinuria
Recurrence
Stem Cells
Immunoglobulin G
Immunoglobulins

Figure

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  Fig. 1 The bone marrow aspirate shows immature nucleated cells comprising approximately 57% plasma cells (Wright stain, ×400).

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  Fig. 2 Immunofixation of the patient's serum and urine. (A) An IgG-κ monoclonal protein was detected using immunofixation electrophoresis at the initial diagnosis. (B) Serum protein electrophoresis performed 2 months after stem cell transplantation showed 2 M-spikes in the γ region with positive IgM-λ, IgG-λ, and IgG-κ bands on immunofixation. (C) One year and 2 months after transplantation, 3 types of protein were continuously seen, and IgG-κ showed different electrophoretic mobility on electrophoresis than that shown by the initial IgG-κ.

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