Methionine PET Might Be Reliable for the Detection of Low M-Protein-Producing Myelomas.

C-methionine (MET) positron emission tomography (PET) is more sensitive than F-fluorodeoxyglucose (FDG)-PET for detecting myeloma lesion. Many clinical studies support this evidence mainly for multiple myeloma cases of IgG or IgA subtypes. However, this is not confirmed for low monoclonal protein-producing myelomas, such as IgD, IgE, and nonsecretory type. We encountered a 71-year-old man with IgD λ-type myeloma. In this patient, FDG-PET did not reveal any abnormal uptake lesions, whereas MET-PET revealed diffuse bone marrow uptake that relieved after initial chemotherapy. We speculate that the determinants for high serological activity of protein metabolism are transporter system activity or proliferation index.