The impact of extra-musculoskeletal manifestations on disease activity, functional status, and treatment patterns in patients with axial spondyloarthritis: results from a nationwide population-based study

Objective: The aim of this study was to investigate the association of extra-musculoskeletal manifestations (EMMs) with disease activity, functional status, and treatment patterns in a large population-based cohort of patients with axial spondyloarthritis (axSpA). Methods: A stratified random sample of patients with axSpA, drawn from health insurance data, received a survey on disease-related characteristics including history (ever presence) of the following EMMs: inflammatory bowel disease (IBD), psoriasis (PSO), and anterior uveitis (AU). Survey data were linked to health insurance data, gathering additional information on current occurrence (within one year) of EMMs and drug prescriptions. Separate multivariable linear regression models were calculated to determine the association of EMMs with disease activity (Bath Ankylosing Spondylitis Disease Activity Index), and functional status (Bath Ankylosing Spondylitis Functional Index) after adjustment for relevant parameters, including treatment. Results: A total of 1729 patients with axSpA were included in the analyses (response: 47%; mean age: 56 years; 46% female) of whom 6% (9%) had current (ever) IBD, 10% (15%) had current (ever) PSO, and 9% (27%) had current (ever) AU. Ever presence of IBD and history of PSO were significantly associated with higher level of disease activity. Ever presence of PSO was also associated with higher level of functional impairment, whereas current AU was significantly associated with lower disease activity. Patients with current IBD or PSO received more frequently biological and conventional synthetic disease-modifying anti-rheumatic drugs as well as systemic steroids. AU was associated with a higher use of conventional synthetic disease-modifying anti-rheumatic drugs only. Conclusion: Disease activity is higher in patients with axSpA with history of IBD or history of PSO. Functional impairment is also higher in patients with axSpA with history of PSO. The presence of different EMMs was associated with different treatment patterns in axSpA.