Diagnostic pitfalls of nonsecretory myeloma manifesting as multiple foci of periosseous plasmacytomas.

Nonsecretory myeloma, which comprises 1-5% of all myelomas, is a variant of plasma cell myeloma. It is defined as symptomatic myeloma without detectable monoclonal immunoglobulin levels on serum or urine immunofixation electrophoresis. Here, we report two cases of nonsecretory plasma cell myeloma that manifested as multi-foci periosseous plasmacytomas. Due to the inability to detect monoclonal immunoglobulin on serum or urine immunofixation electrophoresis and the lack of evidence of clonal plasma cells in the bone marrow, it was difficult to establish an early, accurate diagnosis. Misdiagnosing or mislabeling symptomatic myeloma patients with plasmacytoma results in the delay of their systemic treatment. Therefore, comprehensive imaging studies, the detection of free light chains, and histopathological confirmation from different sites and time points are necessary.