Association of Obesity and Serum Uric Acid with Nail Involvement in Chinese Patients with Psoriasis: A Cross-Sectional Mediation Analysis.

Background: Psoriasis is a chronic immune-mediated systemic inflammatory disease often accompanied by metabolic comorbidities, most notably obesity. Although nail involvement is common in patients with psoriasis, its relationships with obesity and serum uric acid (SUA) remain insufficiently characterized. Aims: This study aimed to characterize the clinical, metabolic, and inflammatory profiles of patients with psoriasis across different body mass index (BMI) groups and to evaluate associations among obesity, SUA, and nail involvement, as well as the potential statistical mediating role of SUA. Methods: This single-center retrospective cross-sectional study stratified adult patients with plaque psoriasis by BMI into normal-weight, overweight, and obese groups. Patient characteristics were compared across BMI groups. Multivariable logistic regression was used to analyze factors associated with psoriatic nail involvement. An exploratory mediation analysis was conducted to assess the potential statistical mediating role of SUA in the association between overweight/obesity and psoriatic nail involvement. Results: A total of 189 patients were included (normal-weight, n = 62; overweight, n = 72; obese, n = 55), and 108 (57.1%) had nail involvement. The proportion of nail involvement increased across BMI groups (43.5%, 59.7%, and 69.1%, respectively; Conclusion: The observed statistical associations of overweight/obesity and elevated SUA with psoriatic nail involvement, together with the exploratory indirect association through SUA, provide further insight into the clinical and metabolic features associated with nail involvement in psoriasis. These findings warrant further confirmation in prospective studies.