Incidence rate of and risk factors for glomerulonephritis in patients with axial spondyloarthritis: a nationwide population-based study.

Background: Although extramusculoskeletal manifestations, such as uveitis and psoriasis, in patients with axial spondyloarthritis (SpA) are well-documented, studies on the occurrence of glomerulonephritis in this population are scarce.

Objectives: This study aimed to assess the incidence rate and risk factors for glomerulonephritis in patients with axial SpA using a nationwide population-based cohort in Korea.

Design: Nationwide population-based study.

Methods: This study included patients diagnosed with axial SpA between 2016 and 2019 from Korea's National Health Insurance Database. Patients with a diagnosis of preexisting kidney disease prior to their axial SpA diagnosis and those diagnosed with glomerulonephritis within 1 year of their axial SpA diagnosis were excluded. For the remaining patients, the incidence rates of glomerulonephritis and Cox proportional hazard ratios were analyzed.

Results: Among the 11,796 patients, 58 had glomerulonephritis, resulting in an incidence rate of 1.82 per 1000 person-years. After adjusting for age and sex, the hazard ratio for patients with a Charlson Comorbidity Index score of ⩾1 was 2.03 (confidence interval (CI), 1.14-3.63; p = 0.017). When adjusting for age, sex, and comorbidities, the hazard ratio for patients with hypertension was 2.37 (CI, 1.20-4.69; p = 0.014). Among the 58 patients, 4 (6.9%) were diagnosed with glomerulonephritis, as confirmed via kidney biopsy.

Conclusion: The incidence rate of glomerulonephritis in Korean patients with axial SpA is lower than that in patients with other musculoskeletal manifestations. In addition, the presence of comorbidities, including hypertension, is a significant risk factor for glomerulonephritis in patients with axial SpA. Despite the low occurrence, careful monitoring for glomerulonephritis in patients with axial SpA is essential.