Comparison between contrast enhanced MRI and FDG PET/TC in the staging, treatment and follow-up of multiple myeloma.

Purpose Multiple Myeloma (MM) is a neoplastic disorder characterised by uncontrolled proliferation of plasma B cells within the bone marrow. MM diagnosis is based on three pathological findings: bone marrow containing more than 10% of plasma cells, generalized osteopenia or bone lesions (demonstrated by imaging) and serum (or urine) abnormal protein. For several decades whole body skeletal radiograph has been the only imaging study available for the assessment of MM. Nowadays, contrast enhanced MRI and FDG PETCT represent the most sensitive imaging techniques in the evaluation of patients affected by MM. The purpose of our study was to compare these two imaging techniques in the staging, treatment evaluation and follow-up of MM. Methods and Materials One hundred and fifty-four patients affected by MM and submitted to MRI of the spine and pelvis and PET-CT, with no more than 15 days between the two exams, were enrolled in the study. Two expert oncologic radiologists retrospectively evaluated all the images. We correlated patients clinical data and laboratory findings with imaging results, evaluating MRI and PET-CT results separately. Patients at MM diagnosis have been staged according to Durie-Salmon plus staging system. Results Fifty-three patients were at diagnosis (group A), 33 at the end of therapy (group B) and 68 in follow-up (group C). In 5/53 (9.4%) patients from group A, PET-CT did not detect any lesion whereas MRI showed diffuse spine involvement; in 2/53 (3.8%) patients from the same group MRI was negative and PET-CT identified lesions out of MRI field of view. Differences between PET-CT and MRI findings determined changes in the staging of 13/53 (24.5%) patients: PET-CT downstaged 12 of them (92.3%), MRI only 1 (7.7%). A good or complete clinical response to therapy was achieved in 24/33 (72.7%) patients from group B: PET-CT showed a faster normalization of imaging findings than MRI in 15/24 (62.5%) (p<0.001). Twelve out of sixty-eight (17.6%) patients from group C presented MM clinical recurrence: MRI identified active lesions in 11 of them (91.7%), PET-CT in only 5 (41.7%) (p=0.031). Conclusion As previous studies has already shown, MRI achieved better results than PET-CT in the staging of the disease. Moreover, in patients with MM recurrence MRI demonstrated to be superior to PET-CT. In these phases of the disease contrast enhanced MRI is higly recommended. However, PET-CT represents the most performant imaging tool in the evaluation of therapy response, showing prompt changes of imaging findings, faster than MRI, in patients with good or complete clinical response after therapy. In addition, PET-CT offers the advantage of a wider field of view than MRI. MRI and FDG PET-CT offer complementary information for the assessment of the disease. The complete knowledge of differences between these two imaging thechniques may be helpful especially for patients evaluated, at one or more steps, by only one of them.