Articular ¹⁸Fluorodeoxyglucose Uptake Is Associated With Clinically Assessed Swollen Joint Count in Patients With Rheumatoid Arthritis

Objective Examination and conventional radiography of joints are unable to precisely evaluate and measure disease activity in rheumatoid arthritis (RA). We quantified joint inflammation using ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography (PET)/computed tomography (CT) in people with RA to determine if PET-derived uptake variables were correlated with RA disease activity measures.

Methods We cross-sectionally studied 34 patients with RA in a substudy of the Rheumatoid Arthritis Study of the Myocardium (RHYTHM). All patients underwent ¹⁸F-FDG-PET scanning with CT for attenuation correction and anatomic co-registration. Linear regression was used to model the associations of disease activity scores with articular FDG uptake, calculated as standardized uptake values (SUVs). Weighted joint volume SUVs (wjSUV) representing 25%, 50%, 75%, and maximum (100%) uptake (wj25SUV, wj50SUV, wj75SUV, and wjMaxSUV, respectively) were calculated as global variables of the total volume of joint inflammation in each patient.

Results Calculated wj25SUV (Spearman ρ = 0.39, P = 0.04), wj50SUV (ρ = 0.39, P = 0.04), and wj75SUV (ρ = 0.37, P = 0.045) measures were significantly correlated with the number of swollen joints. Similar significant correlations were found for the Simplified Disease Activity Index but not Clinical Disease Activity or Disease Activity Score in 28 joints. No associations were found between articular FDG uptake and nonarticular RA-related variables (ie, disease duration, seropositivity, or RA treatments).

Conclusion Articular FDG uptake in patients with RA was significantly correlated with the number of swollen joints but not with biochemical measures of inflammation.