Background Psoriasis is a common chronic immune-mediated skin disease. About 25% of psoriasis patients have psoriatic arthritis (PsA) which is a chronic inflammatory disease affecting the joints, enthesis, and axial skeleton. Delayed diagnosis of PsA is associated with joint damage and disability. Therefore, optimized screening methods including identifying predictors of arthritis in patients with psoriasis have become a medical priority. Collagens are major proteins in all tissues, including skin, bone, cartilage, and connective tissues, which are affected by inflammatory processes present in both psoriasis and PsA. Throughout degradation and remodelling of the extracellular matrix (ECM), proteases cleave collagens leading to protein breakdown products which are released into the circulation. These collagen fragments can be quantified in serum as biomarkers of tissue remodelling and may be helpful in screening patients with psoriasis that have or will develop PsA.

Objectives Our aim is to identify serum biomarkers that can differentiate patients with psoriasis without PsA (PsC) from PsA

Methods Patients with PsC (n=87, mean ±SD age 42.01 ±12.20, 44% female; underwent a full rheumatologic assessment to exclude PsA) and patients with PsA (n=99, mean ±SD age 45.94 ±12.47, 49% female) were recruited at the Toronto Western Hospital, Canada, after appropriate ethics approval. ECM remodelling was estimated using as indices serological anabolic biomarkers quantifying formation of type III, IV, and VI collagen (PRO-C3, PRO-C4, and PRO-C6 respectively), and catabolic biomarkers measuring degradation of type I, III, IV and VI collagen (C1M, C3M, C4M, C6M respectively). Data are presented as mean ± standard deviation (SD). Statistically significant difference between the two groups was calculated by Mann-Whitney U test and a p-value below 0.05 was considered significant. Area under the receiver operating characteristic (ROC) curve (AUC) analysis was performed to describe the discrimination accuracy of each biomarker between the two patient groups.

Results Patients with PsA presented higher levels of C1M, C3M, C6M, and PRO-C6 compared to PsC (p<0.0460-p<0.0009, Figure 1 A, B, D, G), while biomarkers levels of C4M, PRO-C3, and PRO-C4 were not significantly different between PsC and PsA patients (Figure 1 C, E, F). Moreover, C1M and C6M were able to separate between PsC and PsA patients with an AUROC=0.6277 (p=0.0027) and AUROC=0.6446 (p=0.0010), respectively, indicating that these biomarkers may be markers of joint involvement (Figure 1 H, I).

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Conclusion This work provides evidence that serum degradation biomarkers of type I and VI collagen were able to differentiate patients with PsA from PsC and may be potential biomarkers of inflammatory systemic musculoskeletal involvement. These findings suggest that serological biomarkers may be used to identify the 25% of psoriasis patients that have PsA.

Disclosure of Interests Solveig Skovlund Groen: None declared, Signe Holm Nielsen Employee of: Signe Holm Nielsen is employed by Nordic Bioscience, Anne-Christine Bay-Jensen Shareholder of: Anne C. Bay-Jensen holds stock in Nordic Bioscience, Employee of: Anne C. Bay-Jensen is employed by Nordic Bioscience, Mozhgan Rasti: None declared, Darshini Ganatra: None declared, Katerina Oikonomopoulou: None declared, Vinod Chandran: None declared.