High-resolution ¹⁸F-FDG PET/CT for assessing disease activity in rheumatoid and psoriatic arthritis: Findings of a prospective pilot study

Objective: Rheumatoid arthritis (RA) and psoriatic arthritis (PsA) commonly affect the small joints of the wrist and hand. We evaluated the performance of a new, highresolution extremity positron emission tomography (PET)/CT scanner for characterizing and quantifying pathologies associated with the two arthritides in the wrist and hand joints. Methods: Patients with RA or PsA underwent fluorine-18 fludeoxyglucose (¹⁸F-FDG) PET/CT wrist and hand imaging, respectively, on the high-resolution scanner. Calibrated CT images and co-registered PET images were reconstructed. PET/CT was derived for the radiocarpal and pisiform-triquetral compartments, joints with erosive changes, sites of synovitis or tenosynovitis and the nail bed and were correlated with clinical and MRI findings. Results: Significantly elevated ¹⁸F-FDG uptake was measured for the radiocarpal and pisiform-triquetral compartments and at sites of bone erosion, synovitis, pannus and oedema, compared with unaffected joints (p<0.05) in patients with RA, consistent with their clinical findings. In patients with PsA, significantly elevated ¹⁸F-FDG uptake was measured for joints with synovitis compared with unaffected joints (p<0.05), with patterns of ¹⁸F-FDG uptake along the tendons, at the enthesis and in the nail bed, consistent with tenosynovitis, enthesitis and nail dystrophy, respectively. Conclusion: High-resolution ¹⁸F-FDG PET/CT imaging of the wrist and hand is feasible in an RA or PsA patient cohort and is capable of providing quantifiable measures of disease activity (synovitis, enthesitis, oedema and bone destruction). Advances in knowledge: High-resolution PET/CT imaging shows promise as a tool for understanding the pathogenesis of the arthritic process and for noninvasive, objective assessment of RA or PsA severity and therapy selection.