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Letters to the Editor |
1 Institute of Laboratory Medicine, Department of Clinical Chemistry and Transfusion Medicine2 Institute of Clinical Neuroscience, Department of Experimental Neuroscience and3 Section of Hematology and Coagulation, Institute of Internal Medicine, The Sahlgrenska Academy at Göteborg University, Gothenburg, Sweden
aAddress correspondence to this author at: Department of Clinical Chemistry and Transfusion Medicine, Sahlgrenska University Hospital, SE-413 45 Göteborg, Sweden. Fax 46-31-828458; e-mail henrik.zetterberg{at}clinchem.gu.se.
To the Editor:
Capillary zone electrophoresis (CZE) of serum proteins has developed into a rapid and sensitive analytical technique that is gaining impact in clinical laboratories because of its suitability for automation (1)(2). We report a case of plasmacytic lymphoma with an IgM monoclonal gammopathy that was difficult to detect by CZE.
The patient was a previously healthy 49-year-old man who was referred because of palpable large (1.5-cm) lymph nodes bilateral in the submandibular region, in the neck, and in the axillae. Computed tomography scans revealed several large (1–1.5 cm) mediastinal and retroperitoneal lymph nodes. His blood hemoglobin concentration was 120 g/L, his leukocyte count was 6.6 x 109/L, and his platelet count was 361 x 109/L with a normal differential count. Serum total lactate dehydrogenase activity was 4.8 (cutoff for reference interval, <8) µkat/L, and serum ß2-microglobulin concentration was 2.6 (<2.7) mg/L. Biopsy from one of the cervical lymph nodes showed a plasmacytic non-Hodgkin lymphoma with the following immune phenotype: CD20+, IgM+, 
+, 
–, CD5–, CD10–, CD23–, bcl-2+, cyclin D1–. Bone marrow trephine biopsy showed 50–60% cellularity, dominated by normal erythropoiesis but with a paratrabecular lymphoid infiltration with -clonal, CD20+ cells showing plasmacytoid differentiation. There were no lymphoplasmacytic cells in the bone marrow smear.
CZE of serum proteins performed with the multichannel, automated Paragon CZE 2000 instrument with seven capillaries in parallel and software version 1.6.02 (Beckman Coulter) did not reveal any obvious monoclonal paraprotein, and there were no detectable decreases in the concentrations of polyclonal immunoglobulins (Fig. 1A
). However, immunochemical quantification of IgG, IgA, and IgM with use of the Immage system (Beckman Coulter) revealed a high IgM concentration of 32 g/L.
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To further investigate the possibility of an IgM-type paraprotein, we treated 500 µL of serum from the patient with 5 mg of D/L-penicillamine (cat. no. P-5125; Sigma) at 37 °C for 1 h, a treatment that cleaves disulfide bonds in the IgM pentamer through the thiol activity of penicillamine. CZE analysis of the treated sample revealed a monoclonal gammopathy (Fig. 1B
) that was also visible in an untreated sample after agarose gel electrophoresis (Fig. 1C
) and was classified by agarose immunoelectrophoresis as a monoclonal IgM- protein.
Problems with the detection of monoclonal components by CZE have been described previously (3)(4)(5), and a report similar to this one has appeared (6). This case underscores the necessity of combining CZE analysis of serum proteins with immunochemical quantification of the immunoglobulins, using a system with thorough testing against antigen excess to avoid false-negative results. It also describes an old experimental procedure that may be useful when a monoclonal IgM-type paraprotein is suspected and the CZE analysis is inconclusive: penicillamine treatment of the sample.
References
M-protein by capillary electrophoresis [Letter]. Clin Chem 2001;47:1326-1327.The following articles in journals at HighWire Press have cited this article:
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  I. Infusino, P. Luraschi, M. Panteghini, and C. Franzini Pretreatment of serum with penicillamine: effects on capillary electrophoresis patterns and on immunonephelometric measurement of immunoglobulins. Clin. Chem., April 1, 2006; 52(4): 772 - 774. [Full Text] [PDF]
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