Psoriatic arthritis (PsA) and ankylosing spondylitis (AS) are chronic inflammatory diseases within the spectrum of spondyloarthritis, characterized by immune-mediated inflammation and progressive functional impairment. Meteorin-like protein (Metrnl) is a novel adipomyokine with potential immunomodulatory and anti-inflammatory properties; however, its role in spondyloarthritis remains incompletely understood. This study aims to evaluate serum Metrnl levels in patients with PsA and AS compared with healthy controls and to investigate their association with disease activity, inflammatory markers, and clinical manifestations. The findings may provide insights into the potential role of Metrnl as a biomarker of disease activity and inflammation in spondyloarthritis.

Ankylosing spondylitis (AS) and psoriatic arthritis (PsA) are chronic inflammatory disorders within the spectrum of spondyloarthritis, characterized by immune-mediated involvement of the axial skeleton, peripheral joints, and entheses. Despite advances in understanding their pathogenesis, the precise molecular mechanisms underlying disease activity and progression remain incompletely defined, highlighting the need for novel biomarkers and therapeutic targets.

Cytokines play a central role in the pathophysiology of spondyloarthritis by regulating inflammatory pathways and immune responses. Recently, attention has shifted toward newly identified cytokine-like proteins with immunometabolic functions, including meteorin-like protein (Metrnl), also referred to as interleukin-41. Metrnl is an adipomyokine expressed in various tissues, including skeletal muscle and adipose tissue, and is involved in immune regulation and inflammatory processes.

Emerging evidence suggests that Metrnl exerts dual immunomodulatory effects, contributing to both pro- and anti-inflammatory pathways depending on the disease context. It has been shown to influence macrophage activation and cytokine production, thereby playing a role in immune homeostasis (5,6). In addition, recent studies have demonstrated a potential association between circulating Metrnl levels and disease activity in inflammatory conditions, including ankylosing spondylitis.

However, data regarding the role of Metrnl in psoriatic arthritis are scarce, and comparative studies between AS and PsA are lacking. Therefore, this study aims to evaluate serum Metrnl levels in patients with ankylosing spondylitis and psoriatic arthritis and to investigate their association with disease activity and inflammatory markers.

Inclusion Criteria:

• patients diagnosed with ankylosing spondylitis (AS)and psoriatic arthritis (PsA), in addition to age- and sex-matched healthy controls.

AS diagnosed according to the modified New York criteria, while PsA was diagnosed based on the CASPAR criteria.

Exclusion Criteria:

Patients under the age of 18 years, patients with other autoimmune diseases, diabetes mellitus, chronic kidney or liver disease, active infection, or malignancy were excluded to avoid confounding factors affecting inflammatory markers.

AS diagnosed according to the modified New York criteria, while PsA diagnosed based on the CASPAR criteria,