Over the past few years, PDS has proved to be a sensitive tool for assessing disease activity at small‐joint level, by detecting short‐term reduction in synovial perfusion and showing underestimated persistence of active synovitis in patients with chronic arthritis receiving steroids or biological treatment.7,8,9,10
In a recent study,7
our group evaluated PDS signals in the small joints of hands, wrists and feet in 20 patients with chronic arthritis, and showed a high positive interobserver reproducibility (the interobserver κ value for agreement between the two examiners for PDS findings was 0.953 (SE 0.159) at baseline and 0.901 (SE 0.201) at follow‐up examinations, with κ
1 showing the perfect agreement). A good interobserver reproducibility has also been reported by other investigators.6,15
A limitation of this study is the fact that PDS signals were not assessed in the periarticular soft tissues. This relates to the methods used, which relies on the previous experience reporting a good interobserver reproducibility only in assessing intra‐articular PDS signals.7
To the best of our knowledge, this is the first study aimed at assessing the ability of PDS to evaluate changes in synovial perfusion induced by adalimumab in patients with rheumatoid arthritis. The potential value of PDS in treatment monitoring has been evaluated in only a limited number of patients with rheumatoid arthritis treated with steroids or other anti‐tumour necrosis factor α agents.7,8,9,10
At follow‐up examinations after 2 weeks of treatment, a decrease of at least 1 point in PDS score was detected in 79% of wrists. This improvement was comparable with that induced by an intra‐articular steroid injection in the small joints of patients with chronic synovitis.7
Interestingly, at week 12, the number of wrist joints with a PDS score of 0 was six times that at baseline. Although 60% of the wrists still showed the presence of PDS signals, only one wrist had a PDS score of 3, and 66% of wrists positive for the presence of intra‐articular PDS signal had a PDS score of 1.
The correlation between PDS score and changes in DAS28, although positive, is not strong. In fact, there were patients with a consistent improvement in DAS28 score, whose synovial tissue at the wrist level still showed the presence of PDS signals. This can be explained by the fact that PDS is a sensitive tool for showing even minimal increases in synovial perfusion at the small‐joint level, which can be missed by both clinical and laboratory evaluations.
Our study suggests that PDS is a feasible and sensitive imaging tool for assessing the response to treatment of synovitis at the small‐joint level. In particular, we have shown that the wrist joint is a suitable anatomical site to be assessed by PDS for detecting changes in synovial perfusion induced by systemic drug treatment.
Ongoing follow‐up will add further insight into the persistence of considerable reductions in PDS scores and their correlation with DAS28. In particular, long‐term follow‐up will provide information on the predictive value of rapid PDS signal reduction for sustained remission of the disease at the small‐joint level.