FDG PET Imaging of Extremities in Rheumatoid Arthritis

The primary objective of this study was to evaluate the utility of fluorodeoxyglucose positive emission tomography imaging in assessing the degree of joint inflammation and response to therapy in patients with rheumatoid arthritis using standard PET parameters.

Five subjects with newly diagnosed RA were enrolled in this IRB-approved prospective study. After standard conventional workup that included clinical and laboratory evaluation and disease activity score (DAS3v) calculation, subjects underwent baseline FDG PET scans of their hands and feet prior to initiation of treatment and after six months of standard treatment. The uptake of FDG in involved joints was assessed qualitatively (visual evaluation) as well as semi quantitatively using standardized uptake value (SUV). Findings from the FDG PET scans were correlated with clinical and laboratory parameters including DAS and ESR.

In all five patients, increased FDG uptake was noted in various joints affected by RA. The intensity of uptake varied from mild to intense (SUVmax values from 3.10 to 6.0). Overall, these correlated well with the clinical evaluation of involved joints. FDG PET imaging provided additional information by showing involvement in joints that were difficult to evaluate clinically (e.g. mid foot joints). The PET data also provided a distribution of joint involvement with varying degrees of severity in the same subject. On objective analysis using Spearman rank correlation coefficient for statistical analysis, no significant correlations were observed (p>0.05) between DAS, ESR, and the different PET parameters at baseline (before treatment) despite large calculated positive correlation coefficients. This was due to the small sample size (n=5). At post-treatment, the significant correlations were those between DAS and Maximum metabolic disease burden (MDB max) (RS=0.9, p=0.04) and between ESR and MDB max (RS=0.9, p=0.04). The positive correlations between total metabolic disease burden (Total MDB) and DAS (RS=0.7) and between Total MDB and ESR were also large (RS=0.7) but not significant. The non-significance was due to the small sample size.

FDG PET imaging provides a unique noninvasive quantitative method in assessing disease status and response to therapy and can serve as a useful adjunct to clinical evaluation in management of patients with rheumatoid arthritis.