Introduction Musculoskeletal ultrasonography (US) is an objective tool for the evaluation of disease activity in rheumatoid arthritis (RA) patients. There is no consensus on the exact number of joints that should be examined. Examination of reduced joint count is more practical than the comprehensive one.

Objectives This is a cross-sectional study investigated the validity of a 7-joint US score (US7) in assessment of joint inflammation in RA patients compared with a simplified 12-joint US score (US12) and correlated both to composite disease activity indices.

Methods The activity status of 50 RA patients was assessed clinically and ultrasonographically. The disease activity was calculated using 3 composite indices. Ultrasonography was performed by 1 blinded rheumatologist, using power Doppler (PD) and gray-scale (GS) US examination. The US7 and simplified US12 were performed as originally described. However, the GS synovitis and PD synovitis of US12 were computed in 2 separate scores instead of 1. Two sum US7 scores were added, sum (GS) US7 and sum (PD) US7 after summating synovitis and tenosynovitis scores. Ultrasonography interobserver/intraobserver reliability was evaluated on 40 stored images.

Results Correlation coefficient between the different ultrasonographic scores showed no difference. The GS scores showed no correlation with disease activity parameters; however, the PD scores did. The sum (PD) US7 was the only score that showed significant correlation with the 3 different composite disease indices.

Conclusions All studied US scores proved valid in assessment of disease activity status in RA. This is in favor of using the less-time-consuming US7 scores. The strongest correlation found with sum (PD) US7 confirmed the importance of incorporating the tendon in the disease activity assessment.