Psoriatic arthritis (PsA) is a chronic inflammatory arthropathy characterized by enthesitis and synovitis associated with psoriasis, which lead to progressive articular cartilage and bone destruction, and new bone formation [1]. Emerging evidence suggests that psoriasis and PsA are different manifestations of the same underlying disease spectrum. They share many genetic susceptibility loci and common inflammatory pathways [2]. The progression from psoriasis to synovio-entheseal inflammation undergoes distinct phases. The preclinical phase is characterised by abnormal immune system activation, notably involving the IL-23–IL-17 axis and Tumor necrosis factor (TNF) production, triggered by factors from the skin, intestinal mucosa (i.e., the microbiome), or entheses. Subsequently, a subclinical phase ensues, during which soluble biomarkers and specific musculoskeletal alterations are detectable via imaging techniques like musculoskeletal ultrasonography and Magnetic Resonance Imaging [3]. The Moll and Wright's classification criteria [4] and the Classification Criteria for Psoriatic Arthritis (CASPAR) [5] have been used to define PsA as the presence of inflammatory arthritis with the concurrent existence of psoriasis and seronegativity for rheumatoid factor. Despite the development of these criteria, the lack of a gold standard and the heterogeneity of PsA have yielded considerable variability in estimates of the prevalence of PsA in patients with psoriasis. The prevalence of PsA among patients with psoriasis differs widely across countries and regions, ranging from 6.25% to 48% [6,7], due to multiple confounding factors encompassing environmental conditions, race/ethnicity, gender, and age disparities. The methodological differences between studies also contribute to the heterogeneity of prevalence, including sampling methods, classification criteria, and epidemiologic approaches [8]. Currently, no studies provide standardized global epidemiological data for PsA, accounting for differences among populations in terms of geographical location, gender, or age [6,9,10]. Furthermore, there is a paucity of studies in developing countries to investigate the prevalence of PsA among psoriasis patients, and even scarcely any studies have provided global-based epidemiological data. Consequently, a comprehensive comprehension of PsA epidemiology holds paramount importance for both elucidating the disease's nature and optimizing healthcare resource allocation.

In this study, we reviewed and analysed PsA epidemiology studies over the past 45 years. Furthermore, we constructed a Bayesian hierarchical linear mixed model to generate comprehensive epidemiologic age- and sex-specific estimations in different countries and regions. We aim to increase the accessibility of PsA epidemiological data, especially for researchers in areas with inadequate related studies. Additionally, we aim to assist clinicians to manage the progression of PsA patients more effectively.