Role of 18f-FDG PET/CT in the Management of Multiple Myeloma.

Multiple myeloma (MM) is a malignant plasma cell disorder which involves the skeleton in more than 80% of patients at diagnosis. For almost four decades bone lesions have traditionally been detected by Whole Body X-Ray (WBXR) survey. Over the last years, newer methods of evaluation have been increasingly used for the detection of MM bone disease, including magnetic resonance imaging (MRI) of the spine. In comparison with WBXR, MRI has proven to be more sensitive, although its partial field of view (FOV) is a main limitation in clinical practice. 18F-FDG PET/CT is a non invasive and total body imaging method that may be usefully employed to explore bones and soft tissues in MM, to assess the degree and extent of active MM bone disease, as well as to evaluate response to therapy by distinguishing between active and inactive bone lesions.

Aim of the present study was to compare WBXR survey, MRI and 18F-FDG PET/CT scanning in a series of 28 consecutive patients with newly diagnosed MM. Moreover, we compared post-treatment evaluation with MRI and 18F-FDG PET/CT with clinical response in 14/28 patients who received double autologous transplantation as up-front therapy for MM. All patients underwent WBXR, MRI and 18F-FDG PET/CT at baseline and 3 months after the second transplantation. Findings of 18 F-FDG PET/CT were compared to those of WBXR and MRI with respect to number and site of detected bone lesions.

Results of comparison of 18 F-FDG PET/CT with WBXR at diagnosis were as follows: in 16/28 pts (57%) 18 F-FDG PET/CT detected more lesions, all of whom were located in the skeleton; notably, 9 of these 16 patients had a completely negative WBXR survey. In 12/28 pts (43%) both methods were superimposable.

Results of comparison of 18 F-FDG PET/CT with MRI at diagnosis were as follows: in 7/28 pts (25%), 18 F-FDG PET/CT detected more lytic bone lesions which were all located out of the FOV of MRI (6 bone lesions, 1 soft tissue lesion); in 13/28 pts (46%) 18 F-FDG PET/CT and MRI detected the same number of lesions in the spine and pelvis; in 8/28 pts (29%) MRI detected an infiltrative pattern of the spine, without evidence of lytic lesions, whereas 18 F-FDG PET/CT was negative.

Results of comparison of post-transplantation 18 F-FDG PET/CT and MRI with clinical response were as follows: 5 out of 12 patients with negative 18 F-FDG PET/CT were in clinical CR and the remaining 7 patients were in ³ PR. Only 7 out of 12 patients with negative 18 F-FDG PET/CT had normal MRI.

In summary, in 57% of patients at diagnosis 18 F-FDG PET/CT was more sensitive than WBXR for the detection of lytic bone lesions. MRI of the spine was superior over 18 F-FDG PET/CT in 29% of patients, particularly with a diffuse bone marrow replacement. Based on these data, it can be concluded that careful evaluation of MM bone disease at diagnosis should include both MRI of the spine and 18 F- FDG PET/CT. More data are needed to understand the role of 18 F-FDG PET/CT in assessing response to treatment.