Contrast-Enhanced MRI and FDG PET/TC in the assessment of Multiple Myeloma: a comparison of results in different phases of the disease.

Objective: Contrast-enhanced MRI and FDG PET/CT are the most sensitive imaging techniques for the assessment of multiple myeloma (MM), with far higher diagnostic performance than whole-body skeletal radiographs. To provide an accurate evaluation of the disease, subjects affected by MM are usually submitted to both PET/CT and MRI. However, in patients with poor clinical conditions, MRI cannot be performed. Otherwise, where PET/CT is still not available, patients are evaluated by MRI alone. The aim of our study was to compare these two imaging techniques in the staging, treatment evaluation, and follow-up of MM. Materials and Methods: One hundred and sixty-five patients affected by MM who have undergone contrast-enhanced MRI (1.5-T) of the spine and pelvis and FDG PET/CT have been enrolled in the study. In all patients, MRI was performed within 15 days of PET/CT. All the images have been evaluated by two expert oncologic radiologists. Results: Fifty-five patients were at diagnosis (group A), 38 were at the end of first-line therapy (group B), and 72 were in follow-up (group C). In 5/55 (9.1%) patients from group A, PET/CT did not detect any lesion, whereas MRI showed diffuse spine involvement. In 2/55 (3.6%) patients from the same group, MRI was negative and PET/CT identified lesions out of the MRI FOV. Differences between PET/CT and MRI findings determined changes in the staging (according to the Durie and Salmon PLUS staging system) of 13/55 (23.6%) patients from group A: PET/CT downstaged 12 of them (92.3%) and MRI only one (7.7%). In 27/38 (71.1%) patients from group B, a good or complete clinical response to therapy was achieved: PET/CT showed a faster normalization of imaging findings than MRI in 17 of them (63.0%) (p < 0.001). Thirteen out of 72 (18.1%) patients from group C presented MM clinical recurrence: MRI identified active lesions in 12 of them (92.3%), PET/CT only in 6 (46.2%) (p = 0.031). Conclusion: MRI achieved better results than PET/CT in staging and in patients with MM recurrence. On the other hand, PET/CT showed prompt change of imaging findings, faster than MRI, in patients with positive response to therapy. Patients submitted only to PET/CT at MM diagnosis could be downstaged. Moreover, in MM clinical recurrence some active lesions could be missed with PET/CT alone. In patients who only underwent MRI, after good or complete clinical response to therapies, a slower normalization of imaging findings must be considered.