Background/Purpose:

Anti-citrullinated protein antibodies (ACPA) have been considered a relatively specific marker for rheumatoid arthritis (RA), and may play a role in its pathogenesis. In recent years, it has been shown that ACPA can be found at a greater prevalence among psoriatic arthritis (PsA) patients  (approximately 8% or more) than in the general population.  Also, ACPA have been isolated from the synovial fluid of PsA patients.  Several small anecdotal reports have suggested that PsA patients with positive ACPA may have greater swollen/tender joint counts with more deformities and radiologic changes than ACPA negative PsA patients; however, other studies have suggested no difference.  The present study evaluated whether clinical features differ between PsA patients who are ACPA (+) from those who are ACPA (-).  

Methods: A cross sectional study of patients with physician diagnosed PsA in the CORRONA database, a large national registry of patients with RA and PsA.  ACPA was performed in local labs. ACPA (+) and ACPA (-) PsA patients were evaluated for differences in disease activity, disease severity and immunomodulatory medication use.  Evaluations included: tender joint count, swollen joint count, HAQ, patient global assessment, physician global assessment, DAS 28, CDAI, presence of enthesitis, presence of dactylitis, skin psoriasis activity, presence of Sjogrens symptoms, and radiographic changes (defined by presence or absence of erosions, joint space narrowing and joint deformity).  ACPA (+) and ACPA (-) groups were also assessed for smoking status and the presence of rheumatoid factor (RF) and repeat analysis was done to determine if RF presence contributed to any differences. 

Results: Through 2012, there were 5,363 PsA patients  in the CORRONA database,  17.7% of whom had test results for ACPA: 842 were ACPA (-) and 116 ACPA (+).  There was no significant differences in any measures of disease activity or disease severity (including radiographic changes) or the use of immunomodulatory medications between ACPA (+) and ACPA(-) patients.  Interestingly, ACPA (+) patients had a lower average tender joint count (a mean difference of -0.89; 95% CI -1.78, -0.02).  Further stratification into subgroups based upon the presence of RF did not reveal any clinically important differences with the exception of ACPA (+)/RF (-) group who had a higher swollen joint count (a mean SJC of 4.57, p 0.003).  There was also no difference in smoking status amongst ACPA (+) and ACPA (-) PsA patients.

Conclusion: In a large cohort of PsA patients in clinical practice, there were no differences in disease activity, disease severity (including radiographic changes) or the use of immunomodulatory medications between ACPA (+) and ACPA (-) PsA patients. The data suggest that different than for RA, the presence of ACPA(+) may represent only an epiphenomenon in PsA. The fine specifities of ACPA in PsA patients have not yet been defined.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/anti-citrullinated-protein-antibodies-in-patients-with-psoriatic-arthritis-clinical-relevance/