Differentiating Psoriatic Arthritis From Psoriasis Without Psoriatic Arthritis Using Novel Serum Biomarkers

Objective There is a high prevalence of undiagnosed psoriatic arthritis (PsA) in patients with psoriasis. Identifying soluble biomarkers for PsA will help in screening psoriasis patients for appropriate rheumatology referral. We therefore aimed to investigate whether serum levels of novel markers previously discovered by quantitative mass spectrometric analysis of synovial fluid and skin biopsies performs better than the C‐reactive protein ( CRP ) level in differentiating PsA patients from those with psoriasis without PsA (PsC). Methods In this case–control study, serum samples were obtained from 100 subjects with PsA, 100 with PsC, and 100 healthy controls. Patients with PsA and PsC were group matched for age, sex, psoriasis duration, and Psoriasis Area and Severity Index and were not currently receiving biologic treatment. Using enzyme‐linked immunosorbent assay, 4 high‐priority markers (Mac‐2‐binding protein [M2 BP ], CD 5‐like protein [ CD 5L], myeloperoxidase [ MPO ], and integrin β5 [ ITG β5]), as well as previously established markers (matrix metalloproteinase 3 [ MMP ‐3] and CRP level) were assayed. Data were analyzed using logistic regression. Receiver operating characteristic ( ROC ) curves were plotted. Results In comparisons to controls, CD 5L, ITG β5, M2 BP , MPO , MMP ‐3, and CRP level were independently associated with PsA, while only CD 5L, M2 BP , and MPO were independently associated with PsC alone. In comparisons to PsC, ITG β5, M2 BP , and CRP level were independently associated with PsA. ROC analysis of this model shows an area under the curve ( AUC ) of 0.85 (95% confidence interval [95% CI ] 0.80–0.90). The model that included CRP level alone had an AUC of 0.71 (95% CI 0.64–0.78). Conclusion CD 5L, ITG β5, M2 BP , MPO , MMP ‐3, and CRP level are markers for PsA. The combination of ITG β5, M2 BP , and CRP level differentiates PsA from PsC, and performs better than CRP level alone.