Association of the Presence of Anti–Carbamylated Protein Antibodies in Early Arthritis With a Poorer Clinical and Radiologic Outcome

OBJECTIVE: To assess the prevalence of anti-carbamylated protein (anti-CarP) antibodies in a French cohort of patients with early arthritis and to investigate their association with clinical features, final diagnosis, prognosis, and comorbidities. METHODS: The presence of anti-CarP antibodies among patients with early arthritis in the French Etude et Suivi des Polyarthrites Indifferenciees Recentes (ESPOIR) cohort (n = 720) was determined using enzyme-linked immunosorbent assay. We investigated the prevalence of anti-CarP antibodies in different patient subgroups stratified according to anti-citrullinated protein antibody (ACPA) and/or rheumatoid factor (RF) status. Diagnostic and prognostic values of the test were evaluated in this population. RESULTS: Anti-CarP antibodies were present in approximately one-third of the patients (32.6%) and in 23.6% of the patients who were seronegative for both RF and ACPA. Anti-CarP positivity was associated with a more active disease status at baseline and over time. Anti-CarP-positive patients had a significantly higher Disease Activity Score in 28 joints using the erythrocyte sedimentation rate at month 36 than anti-CarP-negative patients (3.1 ± 0.11 versus 2.8 ± 0.06; P = 0.03). Anti-CarP-positive early arthritis was associated with a higher risk of developing erosions after 96 months of follow-up (55.6% of anti-CarP-positive patients versus 37.3% of anti-CarP-negative patients) (odds ratio 2.1 [95% CI 1.2-3.6]; P = 0.009). This association was particularly true when anti-CarP was associated with ACPA positivity. Moreover, ACPA positivity alone in early arthritis was not associated with a higher risk of erosive evolution. CONCLUSION: Our findings indicate that anti-CarP antibodies are present in one-third of patients with early arthritis and in one-fourth of the RF-negative and ACPA-negative patients. They are particularly associated with a more severe radiographic outcome. Anti-CarP antibody positivity may help to accurately identify those at risk of erosive evolution in an early arthritis population.