The Missing M Band: Is it Really Non Secretory Multiple Myeloma?

Non-secretory multiple myeloma (NSMM) is defined as clonal bone marrow plasma cells ≥10% or biopsy proven plasmacytoma, evidence of end-organ damage due to underlying plasma cell dyscrasia, namely hypercalcemia, renal insufficiency, anaemia, bone lesions and lack of serum and urinary monoclonal protein on electrophoresis and immunofixation. They represent 3-5% of multiple myeloma (MM). With the advent of serum free light chain (s FLC) measurement, most of NSMMs have been classified as Light chain Multiple myeloma (LCMM). Thus, the proportion of true NSMM, meaning MM that secretes no monoclonal protein (complete immunoglobulin, heavy or light chain) is close to 1-2% of all myelomas. There is a need to distinguish between the true non-secretory from the other forms of oligo-secretory (OSMM) and secretory form of myeloma like LCMM with use of advanced diagnostic tools such as s FLC assay as the former has a good prognosis.

We discuss a case of a 65-years-old female who presented with chronic chest pain since one year. Cardiac and musculoskeletal involvement were ruled out. Monoclonal gammopathy was suspected in view of imaging abnormalities. Surprisingly, SPE and IFE reported absence of M band. A provisional diagnosis of NSMM was made based on biopsy features. However, diagnosis of NSMM was later changed to LCMM in view of a positive sFLC ratio.

It is well-known that the sequence of diagnostic investigations plays a crucial role in the timely diagnosis and management of patients. However, in this case it was a faulty sequence of ordering investigations which prolonged the hospital stay and delayed therapeutic intervention for the patient concerned. Serum Protein Electrophoresis (SPE), Immunofixation electrophoresis (IFE) and sFLC are simple blood-based tests which can help diagnose a majority of cases of monoclonal gammopathies. They need to be included as first line tests in our approach to evaluating a suspected case of monoclonal gammopathy.