Posttreatment Persistence of Monoclonal Protein on Immunofixation Electrophoresis but Absence on Serum Protein Electrophoresis in a Case of Solitary Bone Plasmacytoma

Laboratory investigations for any suspected case of solitary plasmacytoma of bone include routine biochemical and hematological investigations along with β2-microglobulin, electrophoresis of serum protein and/or 24-hour urine protein, serum protein immunofixation (IFE), and nephelometric quantification of total immunoglobulin isotype and serum free light chain levels. Bone marrow aspirate and trephine biopsy are mandatory to confirm the absence of clonal plasma cells (for solitary plasmacytoma) or the presence of less than 10% clonal cells (solitary plasmacytoma with minimal bone marrow involvement). Imaging studies such as X-ray, computed tomography (CT), magnetic resonance imaging, and positron emission tomography/CT should be used to complement laboratory tests in diagnosis, staging, and defining the local extent of the plasmacytoma. However, guidelines regarding choice of technique for the detection of M band when monitoring a follow-up case of operated plasmacytoma are still not clear. Through this case study, we try to highlight the role of IFE in a follow-up case of operated solitary plasmacytoma of the bone.