Diagnostic Impact of SLiM Criteria in Multiple Myeloma: A Real-World Analysis

Background: Multiple myeloma (MM) has traditionally been diagnosed on the basis of the CRAB criteria (hyperCalcemia, Renal insufficiency, Anemia, and osteolytic Bone lesions), which are used only after permanent end-organ damage has occurred. In 2014, the diagnostic criteria were revised by the International Myeloma Working Group (IMWG) to enable earlier diagnosis, before irreversible organ damage occurs: SLiM criteria (clonal bone marrow plasma cells ≥60%, serum free light chain ratio ≥100, and >1 focal lesion on magnetic resonance imaging) were added to define criteria for myeloma-defining events (MDE; CRAB+SLiM). The aim of this study was to investigate the diagnostic impact of SLiM criteria in real-world clinical practice and explore their relationship with immunoglobulin subgroups. Methods: A retrospective review of 257 MM patients diagnosed at Seoul National University Hospital between January 2016 and June 2020 was conducted. The number and percentage of patients meeting MDE criteria were evaluated, and the frequency of each criteria was analyzed by immunoglobulin subgroups. Results: Among the 257 patients, 96.9% met CRAB criteria, while 3.1% met only SLiM criteria. 76.7% met SLiM criteria, with subgroups having different proportions of patients meeting each criterion. The light chain (LC) subgroup tended to have the highest number of MDE criteria met. Conclusion: The analysis of MDE criteria revealed that the IMWG criteria revised in 2014 led to a slight increase in MM diagnoses (3.2%), from 249 to 257 patients. The addition of SLiM criteria was slightly more helpful in diagnosing MM than traditional CRAB criteria. In subgroup analysis, the LC subgroup tends to meet more CRAB and SLiM criteria than other subgroups, suggesting an association with advanced stage diseases. An increased serum free light chain ratio may indicate underlying plasma cell proliferative disorders.