Analyzing Longitudinal wb-MRI Data and Clinical Course in a Cohort of Former Smoldering Multiple Myeloma Patients: Connections between MRI Findings and Clinical Progression Patterns

SIMPLE SUMMARY: Smoldering multiple myeloma is a heterogenous precursor state of multiple myeloma—both the time until progression and the cause of progression vary within this subgroup. While the number of focal lesions in whole-body MRI (magnetic resonance imaging) is known to be of prognostic value, we investigated whether additional parameters like the size or growth dynamics of focal lesions or precisely quantified diffuse infiltration are connected to risk and cause of progression. We found that both the size and dynamics of focal lesions correlate with progression to multiple myeloma and with existence/appearance of corresponding osteolytic lesions in near-term computed tomography (CT) scans. Furthermore, a score combining intensity and extent of diffuse infiltration showed connections with risk of progression and decrease in hemoglobin. We conclude that these parameters from whole-body MRI can help to predict the clinical course of disease in smoldering multiple myeloma (SMM) patients, with implications for diagnostic follow-up and possibly more specified therapeutic approaches in the future. ABSTRACT: The purpose of this study was to analyze size and growth dynamics of focal lesions (FL) as well as to quantify diffuse infiltration (DI) in untreated smoldering multiple myeloma (SMM) patients and correlate those MRI features with timepoint and cause of progression. We investigated 199 whole-body magnetic resonance imaging (wb-MRI) scans originating from longitudinal imaging of 60 SMM patients and 39 computed tomography (CT) scans for corresponding osteolytic lesions (OL) in 17 patients. All FLs >5 mm were manually segmented to quantify volume and growth dynamics, and DI was scored, rating four compartments separately in T1- and fat-saturated T2-weighted images. The majority of patients with at least two FLs showed substantial spatial heterogeneity in growth dynamics. The volume of the largest FL (p = 0.001, c-index 0.72), the speed of growth of the fastest growing FL (p = 0.003, c-index 0.75), the DI score (DIS, p = 0.014, c-index 0.67), and its dynamic over time (DIS dynamic, p < 0.001, c-index 0.67) all significantly correlated with the time to progression. Size and growth dynamics of FLs correlated significantly with presence/appearance of OL in CT within 2 years after the respective MRI assessment (p = 0.016 and p = 0.022). DIS correlated with decrease of hemoglobin (p < 0.001). In conclusion, size and growth dynamics of FLs correlate with prognosis and local bone destruction. Connections between MRI findings and progression patterns (fast growing FL—OL; DIS—hemoglobin decrease) might enable more precise diagnostic and therapeutic approaches for SMM patients in the future.