Diagnosis of a difficult to differentiate case of early-onset hyperviscosity syndrome caused by IgM type multiple myeloma: a case report.

Hyperviscosity syndrome (HVS) can cause multiple organ damage if not treated immediately. IgM multiple myeloma (IgM MM) is a very rare form of myeloma with clinical features such as elevated serum IgM, and anemia, that resemble Waldenström macroglobulinemia (WM). Distinguishing between these two diseases is important, but can be a challenging problem. It is well known that MyD88 mutations and t(11;14) translocations are useful for differential diagnosis. We diagnosed HVS in a 29-year-old male with IgM MM. He was treated with triplet therapy, autologous hematopoietic stem cell transplantation, and carfilzomib consolidation therapy. His clinical course was monitored by serum IgM levels, and bone marrow myeloma cell counts by multiparameter flow cytometry analysis. After this series of treatments, his HSV disappeared and he reached stringent complete response. In cases of early onset of HVS, IgM MM should be considered in addition to WM.