Background The traditional concept of non-erosive arthritis in Systemic Lupus Erythematosus (SLE) patients changed during the last years, thanks to the use of more sensitive imaging techniques, such as ultrasonography (US). The predictive role of Rheumatoid Arthritis (RA)-specific autoantibodies for bone loss in SLE patients 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 (anti-CarP) antibodies have been demonstrated in seronegative RA patients, with a prevalence of about 16% and a significant association with erosive damage.
Objectives In the present cross-sectional study, we aimed at assessing the association between anti-CarP antibodies and erosive damage in a large cohort of SLE patients with joint involvement.
Methods For this purpose, 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 (arthralgia/arthritis). The clinical and laboratory data were collected in a standardized computerized electronically filled form. All patients underwent blood draws to detect Rheumatoid Factor (RF) and ACPA, by using commercial ELISA kits according to the manufacturer's instructions, and anti-CarP antibodies 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), allowing the possibility to obtain a total score, ranging from 0 to 20.
Results The prevalence of anti-CarP antibodies 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 antibodies was 890.5±794.9 IU/ml. Thirty-nine patients (25.6%) showed erosive arthritis: all the patients referred the occurrence of at least one episode of clinical synovitis. Erosive arthritis was significantly associated with anti-CarP antibodies (p=0.004) and ACPA (p=0.0008). Moreover, a significant correlation between anti-CarP antibody titer and US-erosive score was observed (r=0.2, p=0.01). Of note, anti-CarP antibodies were identified in 24.5% of double negative (ACPA-/RF-) patients, with erosive damage in 25% of them. Interestingly, anti-CarP antibodies resulted significantly associated with the presence of anti-dsDNA (P=0.01).
Conclusions In the present study, for the first time, we identified a significant association between anti-CarP antibodies and erosive damage in SLE-related arthritis, in terms of frequency and severity. We found these antibodies in about 25% of ACPA-/RF- SLE patients, a prevalence higher than that described in seronegative RA patients. Taken together, our results suggest that anti-CarP antibodies could be considered as a candidate biomarker of severity in SLE patients with joint involvement.
Disclosure of Interest None declared