Objective: Ultrasound (US) has become an important tool in the management of rheumatoid arthritis (RA) but it is time consuming in clinical practice. We compared 3 US indices (with different numbers of joints) with disease activity measured by the 28-Joint Disease Activity Score (DAS28) in order to find the most parsimonious index still useful in clinical practice.
Methods: Sixty consecutive RA patients were included. The DAS28 score was calculated by the attending rheumatologist, and later in the day, they underwent US examination by another rheumatologist trained in US (bilateral gray-scale and power Doppler examination of the wrist and metacarpophalangeal and proximal interphalangeal joints). Three different US indices were constructed: index A (22 joints), index B (10 joints), and index C (6 joints).
Results: All 3 US indices were significantly higher in patients with active disease versus inactive disease (P < 0.05 for all 3). Ultrasound index C showed the best correlation with DAS28 (rho = 0.5020, P < 0.0001) and a very good discriminative value for moderate to high disease activity (DAS28 >3.2) and for absence of remission (DAS28 >2.6) (areas under receiver operating characteristic curve = 0.75 and 0.80, respectively). A cutoff value of 3 in US index C showed sensitivity of 88.89% and specificity of 66.67% for absence of remission. Correlation between the 3 US indices was excellent.
Conclusions: A US index of 6 joints (both wrists and second and third metacarpophalangeal joints bilaterally) correlated well with disease activity measured by DAS28 and may be used to evaluate RA patients in daily practice.