Paraskeletal disease in multiple myeloma after treatment: is there a possible prognostic role of whole-body low dose CT (WBLDCT) vs. 18 F-FDG-PET/CT?

Background Post-therapy assessment of paraskeletal plasmacytoma (PM) in multiple myeloma (MM) relies on lesion persistence and/or size changes on whole-body low-dose CT (WBLDCT). Purpose To evaluate the prognostic value of WBLDCT and 18 F-FDG-PET/CT (PET/CT) before and after therapy in newly diagnosed MM patients with PM, and a small subgroup with solitary plasmacytoma (PSO), aiming to refine future imaging response criteria. Methods We retrospectively reviewed PET/CT and WBLDCT images of 42 patients (39 MM, 3 PSO) undergoing first-line therapy from October 27, 2016, to June 12, 2021. Imaging including criteria were a positive PET/CT scan at baseline and a subsequent negative PET/CT scan prior to starting maintenance. Negative PET/CT was defined applying Deauville criteria for focal, PM, and bone marrow uptake, with complete metabolic response defined as uptake below liver background (Deauville scores < 4). PET parameters (IMPeTUs criteria), CT morphological/technical features, and baseline laboratory data were assessed using univariate and multivariate analyses for their impact on clinical outcomes. Results Pre-maintenance SUVmax of the PM lesions predicted adverse progression-free survival (PFS) and Deauville Score 3 identified patients with significantly worse PFS (median 27 months vs. not reached; HR = 3.45, p = 0.05) and showed a trend toward inferior overall survival (OS) (52 months vs. not reached; HR = 2.99, p = 0.16), remaining an independent prognostic factor. In transplanted patients ( n = 32), PM Deauville Score 3 predicted inferior PFS (median 27 vs. 74 months, p = 0.015) and OS (39 months vs. not reached, p = 0.03). CT had limited prognostic value, except for pre-maintenance transverse diameter (PFS: HR = 1.86, p = 0.02) and absence of cortical bone regeneration. Conclusions Pre-maintenance PM Deauville Score 3 has been shown to be representative of adverse outcomes, highlighting the added prognostic value of 18F-FDG-PET/CT over WBLDCT alone, and the possibility of refining future PET monitoring in this patient population.