Association between adiposity and psoriatic arthritis beyond classical clinical predictors.

BACKGROUND: Psoriatic arthritis (PsA) develops in a substantial proportion of patients with psoriasis. Although obesity has been linked to PsA, whether adiposity independently amplifies articular risk beyond established predictors remains incompletely defined. OBJECTIVE: To explore whether adiposity showed a graded association with PsA across different clinical strata. METHODS: This cross-sectional study included 519 psoriatic disease cases (27.2% with PsA). Multivariable logistic regression models assessed the association of waist circumference (per 10 cm) and body mass index (BMI) with PsA, adjusting for psoriasis duration ≥ 10 years, nail involvement, PASI, and sex. Interaction terms between adiposity measures and classical predictors were explored. Model discrimination was evaluated using the area under the receiver operating characteristic curve (AUC), and correlated AUCs were compared using the DeLong test. RESULTS: Nail involvement (OR 3.31, p < 0.001) and psoriasis duration (OR 2.70, p < 0.001) were the strongest independent associations with PsA. An ordinal quartile-based model supported a graded association across waist circumference categories (aOR per quartile increase 1.28, 95% CI 1.05-1.56; p = 0.016). BMI showed a comparable association, and discrimination was similar between adiposity measures (AUC 0.74 vs 0.73; DeLong p = 0.33). No significant interaction was observed between adiposity and psoriasis duration or severity. Exploratory interaction analyses suggested that the adiposity-PsA association may differ according to nail involvement status. CONCLUSIONS: Adiposity was independently associated with the presence of PsA and showed a graded relationship across adiposity levels. These findings support a potential link between metabolic burden and articular disease expression in psoriatic disease.