Differential diagnosis between secondary and tertiary hyperparathyroidism in a case of a giant-cell and brown tumor containing mass. Findings by (99m)Tc-MDP, (18)F-FDG PET/CT and (99m)Tc-MIBI scans.

Brown tumor is one of the skeletal manifestations of hyperparathyroidism. It is a benign but locally aggressive bone lesion and its differential diagnosis with giant cell containing skeletal tumors or metastases may be complicated. We present a male patient with chronic renal failure who was initially misdiagnosed as having a giant-cell rich neoplasm of bone in his right thumb. Diffusely increased fluorine-18 fluorodeoxyglucose ((18)F-FDG) uptake in the axial and appendicular skeleton and multiple (18)F-FDG avid lytic lesions suggesting multiple metastases were observed on the (18)F-FDG positron emission tomography/computed tomography (PET/CT) scan. On the usual technetium-99m methylene diphosphonate ((99m)Tc-MDP) bone scan we noticed diffusely increased uptake in the skeleton and two focuses with very much increased uptake, which suggested a metabolic bone disease rather than a multiple metastatic giant cell tumor or bone metastases. Additional investigation documentated increased levels of parathyroid hormone. Parathyroid hyperplasia was finally diagnosed with (99m)Tc-methoxyisobutylisonitrile (MIBI) parathyroid scintigraphy. Fluorine-18-FDG avid lytic lesions were attributed to hyerparathyroidism associated brown tumors instead of multiple metastases. In conclusion, we present a patient with chronic renal insufficiency, who suffered from secondary and later from tertiary HPT with polyostotic brown tumors, which were best shown by the (18)F-FDG PET/CT than by the (99m)Tc-MDP or the (99m)Tc-MIBI scans.