False-Positive Metastatic Bone Disease on FDG PET/CT Due to Multilevel Tophaceous Gout of the Spine.

A 74-year-old woman was referred for 18 F-FDG PET/CT for the evaluation of incidental CT finding of expansile destruction of left L4/5 facet joint with associated soft tissue mass concerning for a metastatic deposit. The FDG PET/CT revealed variable abnormally increased FDG activity involving multiple facet joints in all regions of the spine with corresponding expansile "punched-out" lytic lesions with sclerotic rims and overhanging margins on CT, raising the possibility of inflammatory polyarthropathy, including gout, as a differential diagnosis. Dual-energy CT of lumbar spine and CT-guided biopsy and culture of the left L4/5 facet joint demonstrated the presence of urate crystal deposition with no evidence of malignancy or infection, confirming the diagnosis of multilevel tophaceous gout of the spine.