The concept of severity in psoriatic arthritis: a scoping review of the literature

Objective: The concept of severity in psoriatic arthritis (PsA) remains inconsistently defined, often conflated with disease activity. This scoping review aimed to explore how severity has been defined in the PsA literature and to identify criteria used to characterize severe disease. Methods: A scoping review was conducted in April 2025 following PRISMA-ScR guidelines. PubMed was searched for English-language articles from the last 25 years, alongside abstracts from major rheumatology conferences. Eligible studies had to explicitly define or discuss PsA severity. Articles focusing solely on activity, isolated disease manifestations, or other conditions were excluded. Data were extracted on the type of article, definitions of severity, and criteria used. Results: Of 4,014 records screened, 32 studies met inclusion criteria. Definitions of severity varied widely and were categorized into imaging (e.g., erosions), clinical (e.g., dactylitis, joint counts), and functional (e.g., HAQ-DI scores) criteria. The most commonly used indicators were structural damage, polyarticular involvement, dactylitis, arthritis mutilans, and validated composite indices such as CPDAI. Only a few studies incorporated functional impairment or patient-reported outcomes. While some guidelines, including GRAPPA and ACR/NPF, proposed multidomain frameworks, a standardized definition remains lacking. Conclusion: The concept of PsA severity has evolved beyond mere disease activity to encompass long-term outcomes, radiographic damage and overall disease burden. However, considerable heterogeneity persists across studies, reflecting the complexity of PsA. A standardized, multidimensional definition of severity, distinct from disease activity, would enhance patient stratification, guide treatment decisions, and support clinical research.