SAT-526 Use of Trabecular Bone Score for Risk Stratification of Patients with Monoclonal Gammopathy of Unknown Significance

Background Monoclonal gammopathy of unknown significance (MGUS) is a common clinical finding, affecting greater than 3% of adults age 50 years or older. There is good epidemiological evidence that patients with MGUS suffer from significantly increased fracture risk. There are, however, no guidelines for evaluation and/or management of skeletal health in patients with MGUS. Trabecular bone score (TBS), a texture index derived from standard lumbar spine (LS) DXA images, provides information about the underlying trabecular bone microarchitecture independent of bone mineral density (BMD). We hypothesized that patients with MGUS have reduced trabecular microarchitecture that would be reflected by lower TBS, findings that might alter skeletal clinical care decisions. Methods We retrospectively identified 115 adult patients diagnosed with MGUS (cases) between 2005 and 2018 who had a LS DXA within 24 months prior to MGUS diagnosis. MGUS diagnosis was as defined by the 2003 International Myeloma Working Group criteria. A control group was identified, matched 1:1 for sex, age (±5 years) and BMI (± 2 kg/m(2)). Exclusion criteria included the presence of primary or metastatic bone malignancy, multiple myeloma, exposure to skeletal anti-resorptive or anabolic agents, or exposure to glucocorticoids for > 3 months. TBS analysis was performed retrospectively using TBS iNsight v3.0 software. TBS values were categorized as low (<1.20), intermediate (1.20 - 1.35) or normal (>1.35). Results Cases had a median age of 69.7 years (IQR 63.7 - 75.8; p=0.98 for cases vs. controls) and were predominantly Caucasian (96%; n=111), men (77%; n=89), and had a median BMI of 28.3 kg/m(2) (25.5 - 32.4; p=0.92). BMD was performed after a median of 24 months from time of MGUS diagnosis (0 - 68 months). Cases had significantly higher incident fractures compared to controls (14 vs. 7, respectively, p<0.05). There was no difference between cases and controls with respect to TBS categorization (low 23 vs. 15%; intermediate 42 vs. 41%; normal 35 vs. 44%; p=0.22) or LS T-scores (-0.30 vs. +0.22, p=0.16). Although fractures occurred in controls with significantly lower TBS values (1.17 vs. 1.34 in controls with vs. without fracture, respectively, p <0.01), this was not the case in patients with MGUS (TBS 1.28 vs. 1.31 in cases with vs. without fractures, p=0.97). Similarly, there was no difference in LS T-scores in cases with or without fractures (0.29 vs. -0.4, respectively, p=0.3). Conclusion Despite MGUS patients having a significantly increased risk of fracture compared to age-, sex- and BMI-matched controls, neither BMD nor TBS, obtained within 2 years of MGUS diagnosis, were able to risk stratify patients. Indeed, unlike controls, patients with MGUS tend to fracture despite a normal BMD and an intermediate or normal TBS value. More advanced non-invasive measures of bone quality and finite element analysis may be needed to capture this risk.