A 57-year-old woman with 6-year history of IgA-λ 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 11C-methionine (MET) and 18F-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.

Fig. 1
figure 1

Images of the whole body of FDG-PET (a), MET-PET before treatment (b), and MET-PET after treatment (c); and images of the right iliac bone of FDG-PET/CT (d), MET-PET/CT before treatment (e), and MET-PET/CT after treatment (f). FDG-PET showed slight abnormal uptake in only the right iliac bone and fifth lumber vertebra (the maximal standardized uptake value, 2.7) (a, d), corresponding to the osteolytic lesion seen on CT scan (d white arrow). In contrast, MET-PET showed intense uptake in the right iliac bone (e arrowhead), right neck of the femoral bone, fifth lumbar vertebra, sacral bone, and base of the skull (the maximal standardized uptake value, 13.2) (b black arrows). After four courses of bortezomib therapy, MET-PET showed that the abnormal accumulation disappeared (c) (f white arrow). Physiological uptake of FDG was shown in the brain and urinary tract and that of MET was shown in the gastro-intestinal tract, liver, pancreas, urinary tract, and salivary glands

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11C-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 FDG-PET/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 FDG-PET/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.