Positron emission tomography findings in a patient with multiple myeloma of polymyalgia rheumatica-like symptoms caused by paraneoplastic syndrome

A 50-year-old Japanese man was referred to our department with pain in his limb joints persisting for 3 months. Although his joints showed no redness, swelling or tenderness, he had a limited range of motion of his hip and shoulder joints, suggesting a diagnosis of polymyalgia rheumatica (PMR). However, his relatively young age and subacute course along with the absence of morning stiffness made the diagnosis uncertain. We performed positron emission tomography/CT, which revealed 18F-fluorodeoxyglucose uptake in bilateral upper and lower joints, consistent with PMR. There was also uptake by a sacral tumour, suggesting a diagnosis of paraneoplastic syndrome. Immunoglobulin A-κ type M protein was detected in serum and bone marrow aspiration/biopsy identified diffuse proliferation of atypical plasma cells, confirming a diagnosis of multiple myeloma. The patient received chemotherapy, which alleviated his limb pain, and achieved stringent complete remission after autologous peripheral blood stem cell transplantation.