The association of hypocomplementemia with disease activity in systemic sclerosis.

Aim: Hypocomplementemia constitutes one of the ten parameters needed to determine the European Scleroderma Study Group (EScSG) disease activity score. However few studies have investigated the clinical manifestations and relationship to disease activity of hypocomplementemia in systemic sclerosis (SSc).The objective of this study was therefore to determine the clinical features of hypocomplementemia in SSc and define its utility as a marker of disease activity. Method(s): 1140 patients from the Australian Scleroderma Cohort Study, comprising a total of 2867 visits were included. These patients fulfilled the 2013 ACR classification criteria for SSc. Demographic, serological and clinical data obtained through annual review were analysed using univariate methods. Linear and logistic regression, together with generalised estimating equations were used to determine the independent correlates of hypocomplementemia ever, and at each visit, respectively. Result(s): At least one episode of hypocomplementemia (low C3 and/or low C4) occurred in 24.1% of patients over a follow-up of 3.4 +/- 1.7 years, these patients were more likely to be seropositive for anti-ribonuclear protein (odds ratio [OR] = 3.8, p = 0.002), anti-Ro (OR = 2.2, p = 0.002), anti- Smith (OR = 6.3, p = 0.035) and anti-phospholipid antibodies (OR = 1.4, p = 0.021) and display features of mixed connective tissue disorder (OR = 1.5, p = 0.007), specifically polymyositis (OR = 16.0, p = 0.012). No association was found between hypocomplementemia and the EScSG disease activity score (calculated without hypocomplementemia to avoid over correlation) or any of its components (including ESR). Among patients with overlap disease features (n = 221), those who were hypocomplementemic were more likely to have a lower BMI (OR = 0.9, p < 0.0005), digital ulcers (OR = 1.6, p = 0.034), tendon friction rubs (OR = 2.4, p = 0.037) and a forced vital capacity <80% predicted (OR = 2.9, p = 0.008) at that visit. Conclusion(s): Hyp