Epidemiology of anti-neutrophil cytoplasmic antibody-associated vasculitis in Lithuania, 2012-2021: a retrospective cohort study.

OBJECTIVES: The aim of this study was to assess the incidence, prevalence and mortality of anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) in Lithuania.

DESIGN: Retrospective cohort study.

SETTING: Lithuanian National Health Insurance Fund and Causes of Death registries, covering 1 January 2012 through 31 December 2021.

PARTICIPANTS: Patients were identified from national healthcare registries in Lithuania. The following inclusion criteria were applied: 1) diagnosis of eosinophilic granulomatosis with polyangiitis (EGPA), granulomatosis with polyangiitis (GPA) or microscopic polyangiitis (MPA) (diagnosis codes M30.1, M31.3 and M31.7, according to International Classification of Diseases 10th version (ICD-10)) recorded between 1 January 2012 and 31 December 2021; 2) diagnosis of AAV was recorded in the database at least twice with at least 1-month period between the two timepoints; 3) a record of at least once prescribed reimbursed medication-glucocorticoids (prednisolone or methylprednisolone), conventional synthetic disease-modifying anti-rheumatic drugs (methotrexate, azathioprine, hydroxychloroquine and cyclophosphamide) or biological disease-modifying anti-rheumatic drug (rituximab or available biosimilars); and 4) age >18 years at the time of diagnosis.

OUTCOME MEASURES: Data for the analysis included sex, age, ICD-10 code of AAV, the first date of AAV diagnosis and date of death. The study period was subdivided into periods 1 (2013-2015), 2 (2016-2018) and 3 (2019-2021). Temporal trends of the incidence of AAV were assessed. Point prevalence data were recorded. Sex- and age-standardised mortality ratios (SMRs) were calculated. The life expectancy of patients with AAV was estimated by standard single-decrement life-table analysis.

RESULTS: We identified 236 patients with AAV (female, 58%) with an annual incidence of 8.22 per 1 000 000 adult inhabitants (period 1, 9.83; period 2, 6.88; period 3, 7.95). Increasing incidence was noted for MPA (period 1, 0.9; period 3, 2.49). The incidence of GPA (4.89 per 1 000 000 inhabitants per year) was three times higher than the total incidence of EGPA and MPA. The prevalence of AAV per 1 000 000 adult population increased from 35.92 in 2015 to 69.14 in 2021. 40 deaths were recorded during the study period, with a mean age at death of 65.2 (±13.03). AAV was associated with reduced life expectancy compared with the general population, especially when diagnosed at a young age. The SMRs for the total AAV cohort revealed a decreasing trend: 1.79 in period 1 and 1.67 in period 3.

CONCLUSIONS: AAV is associated with increased mortality. During the study period, the incidence of AAV was found to be stable, and the prevalence has increased.