Diagnosis of Multiple Myeloma Through an Atypical Serum Protein Electrophoresis Profile: A Case Report

Multiple myeloma (MM) is usually suspected when serum protein electrophoresis (SPEP) shows a monoclonal peak.However, the electrophoretic pattern can sometimes be hard to interpret at very high protein concentrations.We report the case of a 72-year-old man who presented with non-traumatic neural compression at the L1 level.He had marked hyperproteinemia (total protein 112 g/L), anemia, and rouleaux formation.Initial capillary SPEP showed a broadened, distorted gamma-globulin region without a clearly delineated monoclonal peak.The monoclonal component was reported as exceeding the quantification threshold (>33 g/L).After dilution, repeat analysis showed a prominent monoclonal peak quantified at 55 g/L, and immunofixation identified it as IgG lambda.Bone marrow examination showed 35% plasma cells.Together with anemia, this met the International Myeloma Working Group (IMWG) criteria for MM.The change in the profile after dilution suggests a concentration-related analytical or interpretive limitation, but this mechanism was not formally demonstrated.When an atypical SPEP profile occurs with marked hyperproteinemia and clinical suspicion of a plasma cell disorder, the analytical findings should be reviewed and the sample reanalyzed after appropriate dilution.Immunofixation and bone marrow examination provide complementary diagnostic evidence.Beyond diagnosis, an accurate baseline M-protein value is essential for later assessment of treatment response.