Abstract
BackgroundIn some rheumatic diseases such as systemic lupus erythematosus (SLE), low serum complement (‘hypocomplementaemia’) is a feature of active disease. However, the role of hypocomplementaemia in systemic sclerosis (SSc) is unknown. We sought to determine the frequency, clinical associations and relationship to disease activity of hypocomplementaemia in SSc.MethodsThe study included 1140 patients fulfilling the 2013 American College of Rheumatology criteria for SSc. Demographic, serological and clinical data, obtained prospectively through annual review, were analysed using univariable methods. Linear and logistic regression, together with generalised estimating equations, were used to determine the independent correlates of hypocomplementaemia ever, and at each visit, respectively.ResultsAt least one episode of hypocomplementaemia (low C3 and/or low C4) occurred in 24.1 % of patients over 1893 visits; these patients were more likely to be seropositive for anti-ribonucleoprotein (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 were more likely to display features of overlap connective tissue disease, in particular polymyositis (OR = 16.0, p = 0.012). However, no association was found between hypocomplementaemia and either the European Scleroderma Study Group disease activity score or any of its component variables (including erythrocyte sedimentation rate) in univariate analysis. Among patients with SSc overlap disease features, those who were hypocomplementaemic were more likely to have digital ulcers (OR = 1.6, p = 0.034), tendon friction rubs (OR = 2.4, p = 0.037), forced vital capacity <80 % predicted (OR = 2.9, p = 0.008) and lower body mass index (BMI) (OR for BMI = 0.9, p < 0.0005) at that visit, all of which are features associated with SSc disease activity and/or severity.ConclusionsWhile hypocomplementaemia is not associated with disease activity in patients with non-overlap SSc, it is associated with some features of increased SSc disease activity in patients with overlap disease features.
Highlights
In some rheumatic diseases such as systemic lupus erythematosus (SLE), low serum complement (‘hypocomplementaemia’) is a feature of active disease
In patients without overlap disease features, significant correlates of hypocomplementaemia at each visit included a lower body mass index (BMI) (OR for BMI = 0.91, 95 % CI 0.87–0.95, p < 0.0005) and a lower erythrocyte sedimentation rate (ESR) (OR for ESR = 0.99, 95 % CI 0.97–0.99, p = 0.026). In this longitudinal cohort study of 1140 patients with systemic sclerosis (SSc), we found that low serum complement occurred at least once in 23.4 % of patients over the study period. We found that these patients were more likely to have SSc overlap disease features than patients who were normocomplementaemic (29.5 % vs. 21.5 %, p = 0.007), in particular polymyositis
We found that the prevalence of hypocomplementaemia at recruitment was 13.2 %, which is consistent with previous smaller studies [22, 23]
Summary
In some rheumatic diseases such as systemic lupus erythematosus (SLE), low serum complement (‘hypocomplementaemia’) is a feature of active disease. The role of hypocomplementaemia in systemic sclerosis (SSc) is unknown. We sought to determine the frequency, clinical associations and relationship to disease activity of hypocomplementaemia in SSc. Systemic sclerosis (SSc) or scleroderma is a systemic autoimmune disorder of unknown aetiology associated with substantial morbidity and mortality [1]. As in other systemic autoimmune diseases, disease activity leads to irreversible organ damage. Assessing disease activity is necessary for staging the disease and predicting prognosis. It is useful for distinguishing between those patients requiring aggressive treatment and those for whom symptomatic treatment may be sufficient, as well as for monitoring response to treatment
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