S5A:6 Anti-carbamylated proteins antibodies in sle patients with joint involvement: a possible new biomarker for erosive damage

Purpose The concept of non-erosive arthritis in Systemic Lupus Erythematosus (SLE) changed during the last years, thanks to more sensitive imaging techniques, such as ultrasonography (US), allowing the identification of erosive damage in up to 47% of patients. The predictive role of Rheumatoid Arthritis (RA)-specific auto antibodies has been investigated. In particular, anti-citrullinated peptide antibodies (ACPA) have been identified in about 50% of SLE patients with x-Ray detected erosive arthritis. More recently, anti-carbamylated proteins antibodies (anti-CarP) have been demonstrated in seronegative RA, with a significant association with erosive damage. In the present cross-sectional study, we assessed the association between anti-CarP and erosive damage in a cohort of SLE patients with joint involvement. Methods We evaluated 152 SLE patients (1997 ACR criteria; M/F 11/141, mean ±SD age 46.4±11.3 years, mean ±SD disease duration 144.9±110.5 months) with joint involvement. Clinical and laboratory data were collected in a standardised computerised electronically filled form. All patients underwent blood draws to detect Rheumatoid Factor (RF) and ACPA, by using commercial ELISA kits, and anti-CarP by home-made ELISA (results were expressed in arbitrary units (AU)/ml and values above 340 IU/ml were considered positive). US was performed to assess the bone surfaces of metacarpophalangeal and proximal interphalangeal. At each joint, according with OMERACT definition, the presence of erosions was registered with a dichotomous value (0/1), obtaining a total score, ranging from 0 to 20. Results The anti-CarP prevalence was 28.3%, similar to RF (27.6%) and significantly higher to ACPA (11.2%, p=0.003). The mean ±SD titer of anti-CarP was 890.5±794.9 IU/ml. Thirty-nine patients (25.6%) showed an US-detected erosive arthritis: all the patients referred at least one episode of clinical synovitis. Erosive arthritis was associated with anti-CarP (p=0.004) and ACPA (p=0.0008). A correlation between anti-CarP titer and US-erosive score was observed (r=0.2, p=0.01). Of note, anti-CarP were identified in 24.5% of double negative (ACPA-/RF-) patients, with erosive damage in 25% of them. Conclusions We identified a significant association between anti-CarP and US-detected erosive damage in SLE-related arthritis, in terms of frequency and severity. Our results suggest that anti-CarP could be considered as a candidate biomarker of severity in SLE patients with joint involvement.