Background There is a high prevalence of undiagnosed psoriatic arthritis (PsA) in psoriasis patients. Therefore identifying soluble biomarkers for PsA will help in screening psoriasis patients for appropriate referral to a rheumatologist.

Objectives Our purpose was to investigate whether serum levels of novel markers discovered by quantitative mass spectrometry (MS) of synovial fluid and skin biopsies, differentiate PsA patients from those with psoriasis without PsA (PsC).

Methods Serum samples were obtained from 100 patients with PsA, 100 with PsC, and 100 healthy controls. Subjects were group matched for age and sex. No patient was undergoing treatment with biologics at the time of serum collection. Using enzyme-linked immunosorbent assays, four high-priority markers, previously discovered by quantitative MS of synovial fluid and skin biopsies, were analyzed in the serum: Mac-2-binding protein (M2BP), CD5-like protein (CD5L), Myeloperoxidase (MPO), and Integrin-β 5 (ITGB5), as well as previously established markers Matrix metalloproteinase-3 (MMP3) and C-reactive protein (CRP). Data were analyzed using logistic regression (LR), and receiver operating characteristic (ROC) curves were plotted.

Results The 100 PsA patients (41 females, mean age 51 years) had mean psoriasis duration of 22.9 years, PsA duration of 14.6 years, swollen joint count 3.2, tender joint count 6, and PASI score of 4.7. The 100 PsC patients (45 females, mean age 50 years) had mean psoriasis duration of 20.3 years and PASI score of 4. The 100 controls (52 females) had a mean age of 35 years. Polychotomous LR showed that ITGB5, CRP and M2BP are markers that are significantly different between the three groups. The analyses also showed that CD5L, ITGB5, M2BP, MPO, MMP3 and CRP are independently associated with PsA, while CD5L, M2BP and MPO are independently associated with PsC. When comparing PsA to PsC, ITGB5, M2BP, and CRP were found to be independently associated with PsA (Table 1). ROC analysis (Figure 1) of this model showed an area under the ROC curve of 0.85 (95% CI [0.80, 0.90]) that was superior to CRP only model (AUC 0.68 [0.60, 0.76]).

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Conclusions CD5L, ITGB5, M2BP, MPO, MMP3 and CRP are soluble PsA markers. However, only ITGB5, M2BP and CRP, differentiate PsA from PsC, and is superior to CRP alone.

Acknowledgement This study was funded by Abbvie Canada.

Disclosure of Interest V. Chandran Grant/research support from: Abbvie, D. Cretu: None declared, L. Gao: None declared, K. Liang: None declared, E. Diamandis: None declared