A Case of Clinical Confusion Due to Erroneous M-protein Quantifications: To Splice or Skim?

Abstract

An M-protein identified on electrophoresis is conventionally quantified by integrating the M-spike from baseline (PD), invariably including some irrelevant/background proteins. The use of an alternative approach that skims the M-spike tangentially thereby excluding the background proteins (TS), however, has been scanty. We report herein a case in which PD overestimated the M-proteins inconsistently, leading to confusion over relapse in a multiple myeloma patient. At diagnosis, a 65-year old male had an IgG kappa M-spike of 44 g/L which decreased to 6 g/L (PD) following chemotherapy. Six weeks after autologous stem cell transplantation (ASCT), two M-spikes measuring respectively 10 and 5 g/L emerged. Together with decreases in hemoglobin and blood cell counts, a relapse was suspected. Bone marrow examinations, however, did not reveal any significant plasmacytosis or clonal restriction. Re-analyses by TS reduced the original M-protein estimations by 12% and 88% pre- and post-ASCT respectively, and corroborated the disease activity/status consistently.