Loss of Spleen Visualization on Whole-Body Diffusion-Weighted Imaging in Patients with Multiple Myeloma Is Associated with Poor Prognosis and High Tumor Burden

Introduction Multiple myeloma (MM) is caused by the proliferation of monoclonal malignant plasma cells in the bone marrow (BM). Imaging has played a major role in visualizing myeloma lesions, assessing tumor volume, and predicting the prognosis. Recently, we reported that the total diffusion volume (tDV), assessed using a pretreatment whole-body diffusion-weighted imaging (WB-DWI), was associated with a high BM plasma cells (BMPCs) and a poor prognosis in patients with MM (Terao. et al., Eur Radiol 2021). During that study, we unexpectedly found the frequent absence of a spleen signal in patients with MM and its reappearance after treatment. Therefore, this study aimed to investigate the association between spleen visualization changes on WB-DWI and myeloma tumor load and prognosis in patients with MM. Methods The data of 96 consecutive patients with symptomatic newly-diagnosed MM (NDMM) at Kameda Medical Center from January 2016 to December 2020, 15 consecutive patients with smoldering MM (sMM), and two autopsied spleens of patients with PC dysplasia were retrospectively reviewed. All patients underwent at least one WB-DWI prior to treatment. The detail of WB-DWI was previously reported (Terao. et al., Eur Radiol 2021). "Loss of spleen visualization" (LSV) was defined as a visual loss of the spleen in maximum intensity projection on the WB-DWI (Fig1). The spleen-to-spinal cord (SC) ratio (SSR) was used in each regions-of-interest (ROI) to compare the signal intensity. The spleen ROIs were defined as non-overlapping ROIs of 30-50 pixels. The SC ROI was the largest ROI without overhanging in the image depicting the maximum size of the spleen. This study was approved by the institutional review board and conducted in accordance with the Declaration of Helsinki. All participants provided informed consent. Results The median patient age was 75.5 years and 81 patients (84.4%) were 65 years or older. Almost all patients (n=91) received proteasome inhibitors (PIs) as remission induction therapy and 33 patients received autologous stem-cell transplantation (ASCT). LSV was observed on the WB-DWI of 56/96 (58.3%) patients with NDMM and in one patient with sMM (1/15, 6.7%). Patients with NDMM and LSV had a higher median BMPC infiltration as assessed by CD138-immunohistochemistry (80.0% vs. 50.0%, p<0.001), a higher median tDV (540.2 mL vs. 137.0 mL, p=0.003), higher rate of ISS stage III (p<0.01), a lower SSR (0.36 vs. 0.96; p<0.001), and lower tDV (540.2 mL vs. 137.0 mL; p=0.003) than those without LSV. The three-year PFS (p=0.27) and three-year OS (p=0.021) were lower in patients with NDMM with LSV (PFS: 51.2% and OS: 72.5%) than in patients without LSV (PFS: 63.4% and OS: 100%). Next, we investigated the spleen signal change of patients who underwent WB-DWI twice or more during treatment (n=74). Of 42 out of the 74 patients with LSV at diagnosis, the spleen during treatment became visible on 31/42 (73.8%) patients. Representative patients with various spleen signal changes during treatment are shown in Figure 3 as group A (n=32; patients without LSV at diagnosis and during treatment), group B (n=31; patients who had LSV at diagnosis but the spleen reappeared after treatment), and group C (n=11; patients who had LSV at diagnosis, and despite treatment response, did not regain the spleen signal). Patients in group C showed significantly worse three-year PFS and OS (not available due to early events) than those in group A and B, even after excluding patients who did not achieve partial response or worse (n=11) (Fig1). In the multivariate analysis, the group C retained its prognostic significance for both PFS (hazard ratio [HR], 1.98, 95% confidence interval [CI] 1.00-3.90, p = 0.049) and OS (HR, 5.16, 95% CI 1.27-21.0, p = 0.022) even after adjustment for age over 70 years and the revised-ISS stage III. At last, to investigate the pathological cause of LSV, we reviewed two patients who underwent autopsies, who had both received WB-DWI within 3 months before their deaths (Fig1). One patient showed diffuse myeloma cell infiltration in the spleen and the other showed the amyloid deposition without myeloma cell infiltration. Conclusion This study showed that LSV and a low SSR on pretreatment WB-DWI are correlated with a high tumor volume and poor prognosis. As patients with LSV during treatment had very poor prognosis, the relationships between LSV and other variables should be investigated. Figure 1 Figure 1. Disclosures No relevant conflicts of interest to declare.