Objectives: This study aims to evaluate correlations between spleen signal changes in different MRI sequences and bone marrow plasma cell infiltration as potential indicator of disease burden in multiple myeloma (MM) patients.

Materials and methods: We retrospectively analyzed 45 patients with newly diagnosed MM that underwent whole-body MRI with axial DWI at b-values 50 (b50) and 800 (b800), and coronal T1 and T2 fast spin-echo (T2-TSE) imaging. A subcohort of 39 patients had concomitant [¹⁸ F]FDG PET/CT. The spleen was segmented in all MRI sequences and signal intensities were normalized. MR signal intensities and ADC values were correlated with bone marrow plasma cell infiltration from biopsy, laboratory markers (Beta 2-microglobulin, M-Protein, Red blood count (RBC), Hemoglobin, Hematocrit, Total protein, Creatinine), clinical data (ISS stages, high-risk chromosomal aberrations), and standardized uptake value (SUV) in the spleen as well as spleen-to-liver and spleen-to-blood pool SUV ratios on [¹⁸ F]FDG PET-CT.

Results: Bone marrow plasma cell infiltration was negatively correlated with (normalized) mean splenic signal intensity on DWI-b50, DWI-b800, and T2-TSE images (r = -0.64, p < 0.001, r = -0.58, p < 0.001, and r = -0.66, p < 0.001, respectively) while there was no correlation with the apparent diffusion coefficient or spleen size (p = 0.52). In the subgroup analysis of 39 patients with concomitant [¹⁸ F]FDG PET-CT, there was no correlation of normalized splenic [¹⁸ F]FDG uptake either with MR spleen signal (for T2 p = 0.64) or with bone marrow plasma cell infiltration (p = 0.37).

Conclusions: Our findings reveal a significant association between spleen signal intensity especially on normalized T2-weighted images and tumor burden.

Key points: Question What changes occur in spleen signal on MRI as tumor load marker changes in multiple myeloma (MM)? Findings Spleen signal intensity, particularly on T2-weighted MRI, negatively correlates with bone marrow plasma cell infiltration and laboratory markers of tumor burden. Clinical relevance Standardized quantification of splenic T2 signal is proposed as a new marker for MM disease burden.