Diagnostic performance of skeletal survey versus 18F-FDG-PET/CT for detecting lytic lesions in smoldering multiple myeloma.

8532 Background: Per NCCN Guidelines for smoldering multiple myeloma (SMM), whole body radiography, i.e. skeletal survey (SS), should be used to rule out osteolytic bone lesions. If negative, more sensitive imaging techniques such as whole body 18F-FDG-PET/CT(PET/CT), MRI, or low dose CT should be used to differentiate between SMM and multiple myeloma (MM). The false-negative rate of SS is high (30-70%). The frequency of false-positive SS in SMM is less well known but important because of its common use in community practice. We examine the specificity of SS in patients with a presumed diagnosis of SMM and question if SS is still warranted prior to modern imaging techniques to confirm a diagnosis of SMM. Methods: Records of patients sequentially referred from the community and evaluated for a presumed diagnosis of SMM at the National Institutes of Health Myeloma Program between April 2010 to January 2020 were reviewed. Patients with a SS and PET/CT performed within 30 days were included. Positive findings on PET/CT were defined per the 2014 IMWG criteria as one or more sites of osteolytic bone destruction seen on CT. The sensitivity and specificity of SS were calculated using PET/CT as the reference test. Results: Charts from 144 patients with presumed SMM were reviewed. A total of 76 SMM patients had both a SS and PET/CT performed within 30 days of each other. Sixty-four patients (84.2%) showed concordant results. Twelve (15.8%) patients had discordant imaging results. SS was falsely negative in 3 (4.7% (95% CI: 1.2%-14.2%)) patients and falsely positive in 9 (69.2% (95% CI: 38.9%-89.6%)) patients. SS had a sensitivity of 57.1% (95% CI: 20.2%-88.2%) and a specificity of 86.9% (95% CI: 76.2-93.5). Conclusions: In patients presumed to have SMM, disease burden is low thus highly sensitive imaging modalities are needed to rule out bone disease. This study confirms the low sensitivity of SS in the SMM population. It more importantly points out the low specificity of SS in SMM. The IMWG no longer recommends conventional SS prior to whole body CT (or PET/CT) as first imaging choice in SMM. While the argument may be made that SS should still be used upfront due to low cost and widespread availability, this study shows the risk of overestimating disease. Over 10% of patients in this series had false positive disease on SS and thus at risk of receiving unnecessary treatment. Not only concerning for patient toxicity but more so financial toxicity. If SS is used, it is important to review positive findings directly with a radiologist and consider follow-up confirmatory imaging.