Objective: To investigate the accuracy of composite scores in classifying RA patients who are in remission using the absence of inflammatory activity detected by ultrasound (US) as a gold standard.
Methods: Ninety-seven RA patients who were classified by their rheumatologists as being in remission were studied. Disease activity was assessed by the DAS-28 and simplified disease activity index (SDAI). US examination was performed in mode B and power Doppler (PD) in 42 joints.
Results: Synovial hypertrophy (SH) and PD were present in 92 (94.8%) and 41 (42.3%) patients. If we consider 'remission' to be the absence of joints with PD signal, no differences were found by DAS-28 between patients in remission and those not in remission, although differences were present by SDAI. We then calculated the sensitivity (S), specificity (Sp) and positive likelihood ratio (LR) of different SDAI cut-off points to predict absence of PD signal. SDAI < 5 had an S of 65% (95% CI 52, 76), Sp of 55% (95% CI 39, 69) and LR of 1.45 (95% CI 0.98, 2.15), whereas SDAI < 3.3 had an S of 57% (95% CI 44, 69), Sp of 74% (95% CI 58, 85) and LR of 2.24 (95% CI 1.25, 4.01).
Conclusions: Our results suggest that the SDAI classification of remission is closer to the concept of an absence of inflammatory activity, as defined by the absence of positive PD signal by US.