How long does sonographic joint activity continue in clinically remittive joints of patients with rheumatoid arthritis?

M. Gärtner, F. Alasthi, G. Supp, P. Mandl, JS Smolen, D. Aletaha

Background/Purpose : Ultrasound (US) assessment was shown to be a sensitive tool for the evaluation of inflammatory joint activity in patients with rheumatoid arthritis (RA). Synovial effusion and hypertrophy are evaluated by gray scale (GS), while hypervascularisation, can be measured using power Doppler (PD) signals. Both types of signals are highly sensitive, and may persist even in clinical inactivity. It is conceivable that such subclinical US signals may resolve if clinical inactivity of the respective joint is sustained, but this has not yet been shown during long-term follow-up.

It was the objective of this study to evaluate the persistence of subclinical US signals in previously clinically active joints, which have reached a state of continuous clinical inactivity.

Methods: We performed US imaging of 22 joints of the hands of RA patients, including GS and PD, each graded on a four point scale (0=no, 1=mild, 2=moderate, 3=marked). All joints with no activity by clinical assessment at the same time of the US examination were selected, and we identified the last time point of clinical joint activity (swelling, tenderness, or both). The time between the last clinical joint activity and the current sonographic assessment in that joint was determined and persistence of subclinical US activity was estimated for all patients and all joints using time-to-event analysis.

Results : A total of 90 RA patients with 1980 assessed joints were included in this study: 67.1% (1329) of the joints were positive on GS and 20.7% (410) showed PD signals. The mean±SD number of joints showing signs of sonographic activity was: 15±5 for GS, 5±3.8 for PD.

The median (IQR) time between the last visit exhibiting clinical activity in a single joint and the US assessment in the same joint was 3.6 (1.2;6.3) for joints with PD signals, and 3.5 (1.3;5.6) years for joints with GS signals.

If GS signals were ≥2 we found a significantly shorter time to the last visit with clinical activity compared to joints with GS=1 (median[IQR] 2.6[0.6;2.6] vs. 3.9[1.9;6.6]; p<0.001); for PD signals we saw the same trend (median [IQR] of 2.4[0.5;5.3] for PD≥2 vs. 4.3[1.0;6.2] for PD=1; p=0.066). In joints showing both highly positive GS and PD signals (both≥2), the time to the last clinical activity was even shorter, with a median of 1.4 years. (Figure 1)

Conclusion : We conclude that subclinical joint activity is long lasting in RA joints in clinical remission, but resolves over time. The latter is indicated by a shorter period from last clinical activity for strong signals (PD≥2, GS≥2) as compared to weak signals (PD≤1, GS≤1).

Figure 1: Kaplan Meier curve for subclinical sonographic activity in joints showing GS ≥ 2 and PD signals. GS=grey scale, PD= power Doppler