The complement system plays a fundamental role in mediating the activity of rheumatoid arthritis (RA). Biologic therapy can reduce native complement component levels and its activation. We aimed to study the relation of Doppler ultrasound (US) synovitis versus clinical synovitis with changes in native complement component levels in RA patients on biologic therapy.
This was a cross-sectional study. Ninety-seven consecutive patients with RA on biologic therapy for at least 3 months were recruited. Clinical, laboratory and Doppler US assessments were performed. The Disease Activity Score in 28 joints (DAS28), Simplified Disease Activity Index (SDAI) and a 12-joint US assessment were carried out. Synovitis was semiquantitatively scored in B-mode and power Doppler (PD) mode.
A significant decrease in native complement (i.e. C3 and C4) and C-reactive protein (CRP) levels was observed. This was highly significant for C3 decrease (p<0.0005), and C4 decrease (p<0.0005). Synovitis detected by PD US showed significant negative association with C3 change (p<0.008), where patients with higher C3 change were more likely to have PD US inactive status on assessment.
Our results suggested that disease inactive status determined by PD US but not by clinical assessment can be related with decrease in complement in RA patients treated with biologic therapy.