Association between power doppler ultrasound (PDUS) and disease activity in early rheumatoid arthritis (RA) patients: Results from the idea study

Background: DAS is a validated composite measure of disease activity yet it has limitations in accurately reflecting synovitis; with in particular, the effect of subjective components tender joint counts and patient VAS1. Ultrasound imaging is more sensitive than clinical examination at detecting synovitis and power Doppler (PD) has been shown to correlate with markers of joint inflammation2. Objectives: The aim of this study was to assess the association between PDUS and 28-joint disease activity score (DAS28) in early RA patients receiving treat-to-target (TT) regimen. Methods: Data were obtained from the IDEA study3, a 78-week multicentre controlled trial, double-blinded to week 26. Patients with early RA were randomized to methotrexate (MTX) and infliximab (IFX) or MTX and intravenous methylprednisolone (iv MP), followed by TT regimen. Patients had US assessment at weeks 0, 50 and 78. Sum PDUS score of 18 joints (bilateral metacarpophalangeal 1-5, proximal interphalangeal 2, 3 bilateral, wrists, knees) and 3-variable DAS28 (CRP) were calculated at baseline, weeks 50 and 78. PDUS scores were transformed using ln (PDUS+1). Pearson's product moment correlations between DAS28 and PDUS were determined. Linear regression models were constructed to adjust for DAS28 and PDUS values at baseline, treatment (MTX and iv MP/MTX vs IFX/MTX), age and disease duration. Results: Of the 89 patients scanned, full data were available for 64; 34 (53%) received IFX and MTX and 30 (47%) received MTX and iv MP. Mean baseline DAS28 was 5.5 (SD=1.3). Median (IQR) PDUS at baseline was 10 (5, 17); median (IQR) improvement in PDUS at 50 and 78 weeks was 8 (3, 14) and 9 (4, 16) respectively. PDUS poorly correlated with DAS28 at baseline (r=0.24, p=0.053) but associations were stronger at weeks 50 (r=0.34, p=0.006) and 78 (r=0.616, p<0.001). Associations between changes in DAS28 and in PDUS were moderate at weeks 50 (r=0.41, p=0.001) and 78 (r=0.50, p<0.001). In adjusted models, change in DAS28 was associated with change in ln-transformed PDUS at weeks 50 [coefficient 0.20 (0.01, 0.39), p=0.039; adjusted r-squared=0.42] and week 78 [0.32 (0.20, 0.44), p<0.001; adjusted r-squared=0.74] Conclusions: In an early, DMARD-naive cohort, DAS28 and PDUS did not correlate at baseline but showed improved association with lower levels of inflammation at weeks 50 and 78. Interval change in clinical and ultrasound measures showed moderate correlation, indicating in early RA, DAS28 is reasonably sensitive to change. The relationship in established disease is not as clear. (Figure Presented).