Use of trabecular bone score for risk stratification of patients with monoclonal gammopathy of undetermined significance

Monoclonal gammopathy of undetermined significance (MGUS) is a common finding in clinical practice. The risk for developing MGUS increases with aging in parallel with age-associated increases in fracture risk. Although there is good evidence that patients with MGUS suffer from increased fracture risk, no standardized guidelines exist for the evaluation and/or management of skeletal health in patients with MGUS. Trabecular bone score (TBS), a texture index derived from lumbar spine (LS) dual-energy x-ray absorptiometry (DXA) images, provides information about trabecular microarchitecture independent of bone mineral density (BMD). We retrospectively identified 155 adult patients diagnosed with MGUS between 2005 and 2018. This group was matched 1:1 to a control group for sex, age and BMI. TBS was performed retrospectively, and values categorized as low (≤1.23), intermediate (1.23–1.31) or normal (>1.31). Patients had a mean ± SD age of 69.6 ± 10.0. BMD was performed within a median of 28 months (IQR 1–78) of MGUS diagnosis. Cases had a non-statistically significant higher rate of fractures compared to control subjects (27 vs. 17, respectively, p = 0.1). Patients with MGUS had a significantly lower TBS (1.31 ± 0.13 vs. 1.34 ± 0.12, respectively, p < 0.05) and lower LS BMD (1.215 ± 0.223 vs. 1.275 ± 0.247, p < 0.05) compared to controls. Although fractures occurred more commonly in those control subjects with significantly lower TBS values, this was not the case in subjects with MGUS (TBS 1.299 vs. 1.313 in cases with vs. without fractures p = 0.313). Similarly, there was no difference in T-scores in cases with or without fractures (−1.33 vs. −1.37, respectively, p = 0.56). Despite patients with MGUS having a significantly increased fracture risk compared to age-, sex- and BMI-matched control subjects, neither assessment of BMD nor TBS, obtained within two years of MGUS diagnosis, were able to accurately risk stratify MGUS patients. Unlike control subjects, patients with MGUS tend to fracture despite normal BMD and intermediate or normal TBS values, suggesting that deterioration of cortical rather than trabecular skeletal components may be more important for the increased fracture risk seen in MGUS.