11C-Methionine PET/CT for multiple myeloma

A 57-year-old woman with 6-year history of IgA-k myeloma experienced an increase of serum IgA level from 331 to 683 mg/dl during maintenance therapy with thalidomide after autologous peripheral blood stem cell transplantation followed by allogeneic mini-transplantation. Bone marrow aspiration revealed no sign of relapse of the myeloma. We conducted positron emission tomography/computed tomography (PET/CT) scans using C-methionine (MET) and F-fluorodeoxyglucose (FDG). In MET-PET/CT, there were multiple abnormal hypermetabolic lesions, while FDG uptake in these lesions was faint (Fig. 1). After four courses of bortezomib therapy, MET-PET/CT revealed no abnormal uptake of MET, with decreased serum IgA level (25.3 mg/dl), indicating that MET uptake was correlated with the clinical course, as denoted by IgA level. C-Methionine is a radiolabelled PET tracer that is clinically used for brain tumor. An earlier study reported that MET-PET depicted active myeloma clearly, which might reflect the increased metabolism of amino acids in myeloma cells for producing abundant immunoglobulin [1]. In the present case, MET-PET/CT was very useful for determining the precise localization of the myelomatous lesions and evaluating therapeutic effects. Although FDGPET/CT is reported to have higher sensitivity for localized myelomatous lesions than other imaging modalities, our case suggests the possibility that MET-PET/CT detects myelomatous lesions more clearly than FDG-PET/CT. Considering that in myeloma patients higher FDG uptake or a larger number of FDG-avid lesions is reported to be associated with inferior overall survival and event-free survival, the lower FDG uptake in this patient is possibly related to the slowly progressive nature of her myeloma. In addition, in 30% of myeloma patients, FDG-PET/CT reportedly failed to show the abnormal findings in the spine and pelvis; this may account for the lower FDG uptake in these lesions. Although many imaging modalities, including FDGPET/CT are now widely available, the findings of the present case suggest that MET-PET/CT can provide valuable information for patients with myeloma and has a potential to become an important imaging test. However, further investigation to compare the MET-PET/CT with FDG-PET/CT or other imaging modalities are needed to confirm the diagnostic efficiency and the clinical feasibility of MET-PET/CT for multiple myeloma.