Whole Body MRI and FDG PET in Myeloma

Objectives: Detection of bone marrow abnormalities in patients with multiple myeloma through non-invasive imaging may assist clinicians in choosing optimal treatment strategies. Whole body MRI is a sensitive modality for assessing bone abnormalities and 18F-FDG PET is useful in characterizing functional disease. Both could be complementary in bone assessments. In this work, we evaluate preliminary findings with both imaging techniques and compare them to bone marrow biopsy results.

Methods: We studied 9 subjects (5 females, 4 males; age range 46-73yrs, median age 68yrs) with smoldering multiple myeloma (7 participants) or relapsed, refractory myeloma ( 2 participants). They underwent whole body MR obtained at 3 Tesla using phased array surface and body coils. Axial DWI, coronal STIR, coronal T1 spin echo MR images were obtained from vertex to below the knees. Focal non-degenerative bone marrow signal abnormalities were considered as positive for myeloma involvement. Participants separately underwent whole body 18F-FDG PET/CT approximately 60 minutes after injection with 18F-FDG. PET imaging occurred on the same day or within 2 months of MR, with a median of 20 days. Focal abnormal metabolism in bone was considered positive for disease. Both scans were read without knowledge of the other. Bone marrow biopsy with flow cytometry was usually performed the same day as the PET but always within 10 days. Presence of abnormal plasma cells was considered positive for disease.

Results: PET imaging was negative for suspicious bone findings in 6, positive in 2, and indeterminate in 1 participant. MR imaging was negative in 4, positive in 3, and had heterogeneous bone signal pattern in 2 participants. Both imaging techniques were concordant in 5 scans (3 negative, 2 positive). In the discordant scans, PET was negative and MR had heterogeneous signal in 2; PET was indeterminate and MR negative in one case; and PET was negative while MR was positive in another case. Biopsies and flow cytometry were positive in 4 subjects. Biopsy agreed with the 2 subjects that were concordantly positive on imaging (which were the participants with relapsed, refractory multiple myeloma) but was positive and disagreed in one subject with concordantly negative imaging. Biopsy and flow cytometry positively agreed with MR in the 1 subject that was negative on PET. Bone marrow biopsies were negative in 5 participants which agreed with PET in 4 cases, and MR in 3 cases (2 subjects were concordantly negative on imaging). Bone marrow biopsy was negative in the indeterminate PET study and in the 2 heterogeneous pattern cases of MR. Further characterization and associations with plasma cell histopathology will be forthcoming.

Conclusions: In this preliminary analysis, 18F-FDG PET and/or whole body MR detected bone disease in all but one subject confirmed by bone marrow biopsy. There were 5 negative and positive concordant imaging cases and all agreed with bone marrow biopsy except for one concordantly negative imaging study. The biopsy disagreement with imaging could represent minimal residual disease with a low percentage of abnormal plasma cells. 18F-FDG PET and whole body MR imaging are non-invasive tools that could be useful in myeloma especially when findings are combined.