Whole-Body Macrophage Positron Emission Tomography Imaging for Disease Activity Assessment in Early Rheumatoid Arthritis

Objective To investigate the potential of whole-body positron emission tomography/computed tomography (PET/CT) with a macrophage tracer to image arthritis in patients with early rheumatoid arthritis (RA). Methods Thirty-five previously untreated, clinically active patients with early RA underwent whole-body PET/CT scanning with the macrophage tracer (R)-[11C]PK11195 in addition to clinical assessment (Disease Activity Score in 44 joints [DAS44]). Tracer uptake was assessed quantitatively as standardized uptake values (SUVs). In addition, 2 readers blinded to clinical assessment visually scored tracer uptake in joints. Clinical and PET variables were compared using Cohen , linear regression/correlation, and t tests, where appropriate. Results All but 1 patient showed enhanced tracer uptake in at least 1 joint. Twelve percent of all joints (171/1470) were visually positive on the PET scan, most frequently the small joints in feet (40%) and hands (37%), followed by wrists (15%). Correlations of visual scores with clinical findings both at patient and joint levels were absent or weak. In contrast, average SUVs in the hands, feet, and whole body showed significant correlations with DAS44 scores, with the best correlation seen in the feet (R2 = 0.29, P < 0.01). Conclusion Clinically active patients with early RA had increased joint uptake of a macrophage PET tracer, especially in the feet. Quantitative, but not visual PET measures of whole body and joint groups, particularly the feet, showed moderate and statistically significant correlations with clinical outcome.