Background/Purpose:

Articular manifestations affect a majority of patients with systemic lupus erythematosus (SLE), at least at some time during the disease course. Several investigators have estimated the frequency of erosive arthritis in SLE to about 5%. Detection of antibodies to ‘cyclic citrullinated peptide’ (anti-CCP) is an important diagnostic and prognostic tool in arthritis, since it is highly specific for rheumatoid arthritis (RA) and predictive of erosive disease. While anti-CCP reactivity in RA is citrulline-dependent, it has been suggested that anti-CCP in SLE is generally not, and thus also reacts with the corresponding ‘cyclic arginine peptide’ (CAP). Recently, it has been shown that antibodies targeting carbamylated proteins (anti-CarP) may occur in anti-CCP/rheumatoid factor negative cases even before the onset of RA. We analyzed anti-CCP, anti-CAP and anti-CarP in sera from patients in our well-characterized regional SLE register and related the findings to X-ray data, physical function and smoking habits.

Methods:

We included 236 patients (88% women) in the ‘Clinical Lupus Register in Northeastern Gothia’. 212 had established disease, whereas the remaining 24 had recent-onset SLE at the timepoint of blood sampling. 75% met the ACR criterion for arthritis. Cases were classified as SLE according to any of the following criteria sets: the 1982 American College of Rheumatology criteria (84%) or the 2012 Systemic Lupus International Collaborating Clinics (SLICC-12) criteria (99%). IgG anti-CCP and anti-CAP ELISA kits (Euro-Diagnostica) were used. IgG anti-CarP was quantified with ELISA as previously described. X-ray data (hands, wrists and/or feet) were available in medical records of 91 cases (39%).

Results:

16 patients (6.8%), all meeting SLICC-12, were anti-CCP positive, 9 of whom were also anti-CAP positive. 4 of the 7 patients with citrulline-dependent anti-CCP had a history of biopsy-proven nephritis. 23 patients (9.7%), all meeting SLICC-12, were anti-CarP positive. Only 6 of the anti-CarP positive cases were identified as anti-CCP positive. Neither anti-CCP nor anti-CarP were associated with arthritis judged by physical examination, nor to any other SLE phenotype. The presence of anti-CarP was associated with a positive lupus anticoagulant test (Fisher’s exact test, p=0.019). Smoking habits and HAQ did not associate with any of the antibodies. X-ray-proven erosions were found in 10 patients (4.2%) and were significantly associated with anti-CarP (Fisher’s exact test, p=0.025), whereas the association with anti-CCP did not reach statistical significance (Fisher’s exact test, p=0.07).

Conclusion:

Erosive arthritis is uncommon in SLE and our findings are in line with previous observations reporting a prevalence of 4-5%. Anti-CarP antibodies have previously not been studied in SLE. Herein, we demonstrate that anti-CarP in SLE: (1) is more frequently found than anti-CCP; (2) mainly identifies a different subgroup of cases compared with anti-CCP; and (3) associates significantly with erosive disease.

« Back to 2015 ACR/ARHP Annual Meeting

ACR Meeting Abstracts - https://acrabstracts.org/abstract/anti-carbamylated-protein-antibodies-identify-systemic-lupus-erythematosus-patients-with-erosive-arthritis-analysis-of-a-regional-swedish-register/