Abstract
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 FDG PET-CT (18F-Fluorodeoxyglucose positron emission computed tomography) in people with RA to determine if PET-derived uptake parameters were correlated with RA disease activity measures.
Methods We cross-sectionally studied 34 RA patients in a sub-study of the Rheumatoid Arthritis Study of the Myocardium (RHYTHM). All patients underwent 18F-FDG-PET scanning with computed tomography 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 (SUV). Weighted joint volume SUVs (wjSUV) representing 25%, 50%, 75% and maximal (100%) uptake (wj25SUV, wj50SUV, wj75SUV, and wjMAX SUV) were calculated as global parameters of the total volume of joint inflammation in each patient.
Results Calculated wj25SUV (Spearman rho =0.390, p=0.037), wj50SUV (rho=0.385, p=0.039), and wj75SUV (rho=0.374, p=0.045) measures were significantly correlated with the number of swollen joints. Similar significant correlations were found for the SDAI score but not CDAI or DAS28. No associations were found between articular FDG uptake and non-articular RA-related variables (i.e. disease duration, seropositivity, or RA treatments).
Conclusion Articular FDG uptake in RA patients was significantly correlated with the number of swollen joints but not with biochemical measures of inflammation.