The correlation between ultrasound-detected synovitis of small joints and the clinical disease activity in patients with rheumatoid arthritis

Abstract Background: Rheumatoid arthritis (RA) is chronic inflammatory arthritis with multi-joint involvement, especially small synovial joints in hands and feet. So far, the synovitis of which joint in hands or feet is better correlated with clinical disease activity indices is unknown; the correlation of synovitis detected by ultrasound in an individual joint with global disease activity is unclear either.Objectives: To explore the correlation between the ultrasound-detected synovitis in metacarpophalangeal (MCP), metatarsophalangeal (MTP), proximal interphalangeal (PIP) joints and the clinical disease activity indices in patients with RA.Methods: 30 joints, including bilateral MCP, PIP and MTP, were scanned for synovitis by ultrasound, semi-quantitatively scored for gray scale(GS) and power Doppler(PD). The correlation between Disease Activity Score-28 joints(DAS28), Simplified Disease Activity Index (SDAI), Clinical Disease Activity Index (CDAI) and ultrasound-detected synovitis score in each joint was assessed using Spearman’s rank correlation test. Results: 211 RA patients were included in this study. The whole GS scores of all MCP joints showed highest correlation with all clinical disease activity indices (r=0.403-0.452, p<0.01), followed by PIPs (r=0.318-0.331, p<0.01) and MTPs (r=0.277-0.301, p<0.01). Likewise, the whole PD scores of all MCP joints also showed highest correlation with the disease activity (r=0.332-0.396, p<0.01), followed by PIPs (r=0.211-0.242, p<0.01), and MTPs (r=0.198-0.222, p<0.01). The highest correlation of GS score with DAS28-ESR (r=0.411, p<0.01), DAS28-CRP (r=0.459, p<0.01), SDAI (r=0.444, p<0.01) was observed in MCP3 joint, while with CDAI (r=0.421, p<0.01) in MCP2 joint. The highest correlation of PD score with DAS28-ESR (r=0.353, p<0.01), DAS28-CRP (r=0.399, p<0.01), CDAI (r=0.368, p<0.01), SDAI (r=0.377, p<0.01) was in MCP5 joint. Conclusions: The ultrasound-detected synovitis at MCP joints, especially MCP2, MCP3, and MCP5 joints, was best correlated with composite disease activity of RA, in contrast to PIP and MTP joints. MCP joints should take greater weight in clinical disease activity assessment.