Hypocomplementemia and clinical manifestations in patients with systemic sclerosis

Hypocomplementemia has been observed in systemic sclerosis (SSc). Although complement activation is not commonly thought to be part of the pathogenesis of SSc.  Hypocomplementemia is included as one of items in two frequently used SSc disease activity indexes. There is negotiation about their usefulness to access disease activity. Correlation between clinical manifestations and hypocomplementemia is still not fully studied and only few data are available. This study evaluated correlation of complement components C3 and C4 levels with clinical features in patients with systemic sclerosis. Study subjects consisted of those who met diagnostic criteria for SSc (The ACR/EULAR 2013). Retrospective data of clinical histories and immunological blood tests were analysed of these patients during 2017-2020. A total 82 patients were enrolled in this study. Complement components (C3 and C4) were evaluated in 53 patients during their stay in hospital. Patients were divided in 2 groups – 1st group (9 patients, all were women) with low C3 or C4, 2nd group (44 patients, females 86%, males 14%) – with C3 and C4 in normal ranges. Average age when serum complements were evaluated in 1st group was 67,8 years, in 2nd - 59,95 years. In 1st group positive antinuclear antibodies were observed in all patients (100%), in 2nd group – only 86%, 14% were ANA negative. In the 1st group 5 patients had pulmonary hypertension (55,6%), 100% - Raynaud's syndrome, 22% (2/9 patients) had interstitial lung disease. In the 2nd group – 29,5% had pulmonary hypertension, 84% had Raynaud's syndrome and 48% had interstitial lung disease. Unfortunately, serum complement levels are infrequently evaluated in patients with SSc. Hypocomplementemia was observed only in patients with positive ANA. We found higher prevalence of pulmonary hypertension and Raynaud's syndrome in patients with hypocomplementemia, that requires further investigation of complement activity in these patients.