SMM consists of the following subtypes which represent progression of their corresponding MGUS subtypes. Non-IgM SMM
Non-IgM SMM (also termed IgG and IgA SMM because of the rarity of IgD and IgE SMM) is diagnosed in asymptomatic individuals based on criteria identical to those listed above for Non-IgM MGUS except that: their intact IgG or IgA myeloma protein levels are equal to or greater than 30 grams/liter rather than 15 grams/liter; their bone marrow shows plasma cells comprise between 10% and <60% rather than <10% of nucleated cells; and/or their 24-hour urine contains 0.5 gram or greater levels of Bence Jones, i.e. light chain myeloma, proteins. individuals must also lack evidence of more recently established multiple myeloma-defining criteria viz., CRAB features, amyloidosis, more than one solitary plasmacytoma, and/or serum or urine free light chain κ to λ or λ to κ ratios of 100 or greater.Overall, the risk of Non-IgM SMM progressing to multiple myeloma is 10% per year for the first 5 years but falls off sharply to 3% per year for the next 5 years and thereafter to 1% per year. Smoldering Waldenström macroglobulinemia
Smoldering Waldenström macroglobulinemia is diagnosed in asymptomatic individuals that have a serum IgM level 30 gram/liter and/or a bone marrow lymphoplasmacytoid cell infiltrate >10% of total nucleated cells.
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