Efficacy of serum immunoglobulin free light chain and 18F-FDG PET/CT for therapeutic evaluation in a case with multiple plasmacytoma of bone

Solitary/multiple plasmacytoma of bone, a rare disease as compared to multiple myeloma, is characterized by monoclonal proliferation of plasma cells in local legion (s) of bone, with no bone marrow abnormalities. Monoclonal gammagloblinemia is often absent in these conditions, and useful examinations allowing evaluation of responses to treatment are as yet lacking. Recently, 18F-FDG PET/CT (PET/CT) was reported to be useful for detecting bone lesions. PET/CT is also valuable for predicting the outcomes of patients with solitary plasmacytoma, when applied in combination with the serum free light chain (sFLC) κ/λ ratio. We present a 62-year-old male with multiple plasmacytoma of bone (MPB), in whom PET/CT and the sFLC κ/λ ratio were useful for evaluating the response to treatment. The patient was diagnosed with MPB, with PET/CT showing multiple abnormal tracer uptakes in the scapula, spine, and ribs. The sFLC ratio was markedly elevated, with the κ chain level being especially high. We administered bortezomib and dexamethasone, after which the abnormal uptakes on PET/CT disappeared. The sFLC ratio and the FLC value also normalized, and have remained stable for more than one year, to date, since treatment. In our case, PET/CT and the sFLC κ/λ ratio were found to be extremely useful for monitoring treatment responses.