Rheumatoid factor and anti-citrullinated protein antibodies (ACPA) in psoriatic arthritis (PsA), and skin psoriasis: Relevance and clinical implications

Aim of the workAnti-citrullinated protein antibodies (ACPAs), is a highly specific markers for rheumatoid arthritis, can also be found in psoriatic arthritis (PsA). This work aimed to look into the frequency of rheumatoid factor (RF) and ACPA in PsA and psoriasis patients without clinical evidence of arthritis (PSO), and to correlate findings with demographics, disease characteristics, laboratory findings, and radiological damage in PsA. Patients and methods: The study included 78 PsA patients, 47 PSO patients, and 69 normal controls. Full clinical assessments, RF and ACPA assays, and modified radiological Steinbroker score (Mss) for PsA were performed. Results: The age of the patients was 45.6 ± 8.7 years and the M:F 59:66 (M:F 0.9:1). Positive RF was not significantly different between PsA and PSO groups (p = 0.35), but positive ACPA was significantly more common in PsA patients (p < 0.001) than in PSO and controls. No significant difference was observed between the PSO and controls (p = 0.08). In PsA, RF titers correlated significantly with ESR (p = 0.002), swollen joint count (SJC)(p = 0.02), tender joint count (TJC)(p = 0.02), and mSS (p = 0.001), while in the PSO RF correlated significantly with ESR (p = 0.011) and CRP levels (p = 0.02). In the PsA, ACPA titer significantly correlated with CRP levels (p < 0.001), SJC (p = 0.002), TJC (p = 0.003), mSS (p < 0.001) and PASI (p < 0.001), but with none of these in the PSO. Conclusion: PsA patients have more frequent positive RF and ACPA than PSO patients. ACPA values are significantly correlated with markers of inflammation, swollen and tender joint count and radiological damage in PsA and not in PSO patients.