16. Epidemiology and Clinical Characteristics of Adult-Onset IgA Vasculitis in Southern SwedenMichaela Thalén1

Background: IgA vasculitis (IgAV) is the most prevalent primary childhood vasculitis in Sweden, but the disease is considerably rarer in adults. Patients with adult-onset IgAV have more severe organ involvement and worse long-term renal outcomes compared to children. This study aims to describe the epidemiology, clinical characteristics, and outcomes of adult-onset IgAV in Skåne, southern Sweden. Methods: The study area consisted of Skåne, the southernmost region of Sweden, with an adult (≥18 years) population of 990 464 on 31 December 2010. Adult patients assigned the ICD-10 code D69.0 between 2000 and 2019 were retrospectively identified in a population-based database. Medical records were reviewed to validate the diagnosis of IgAV and abstract data. Patients defined as IgAV according to the 2012 Chapel Hill Consensus Conference Nomenclature of Vasculitides with a biopsy-proven diagnosis were included. The incidence rate and point prevalence (p.p.) were estimated per 1 000 000 adults. The p.p. was estimated on 31 December 2019. Results: Fifty-nine patients (19 women) were classified as having adult-onset IgAV. The median age at diagnosis was 38 (IQR 24−55) years. The annual incidence rate was 3.0 per 1 000 000 adults and was higher among men than women (4.0 vs 2.0/1 000 000, P=0.004). The incidence rate decreased with age, with the highest rate in the group aged 18−27 years (Table 1). The point prevalence was estimated to 45.3 /1 000 000 adults and was higher among men (58.7 vs 31.8/1 000 000, P=0.03). Ninety-seven percent of patients presented with non-thrombocytopenic purpura, 78% with renal involvement, 59% with arthritis/arthralgia and 39% with gastrointestinal symptoms. At onset of the disease, 66% received oral corticosteroids (mean dose 40 ± 19 mg/day), three patients (5%) were treated with oral cyclophosphamide (150 mg/day), and one received plasmapheresis. Sixteen patients (27%) started immunosuppressive treatment later during follow-up, most commonly azathioprine. Patients were followed for a median time of 6.5 (IQR 2.8−11.8) years. One patient (35-year-old woman) developed end-stage renal disease 11 years after diagnosis of IgAV and underwent a kidney transplant. In total, five deaths (8%) were observed. Causes of death included malignancy (n=2), stroke (n=1), femur fracture (n=1) and unknown (n=1). The mean age at death was 83 ± 10 years. Conclusions: The incidence of adult-onset IgAV in southern Sweden was comparable with that described in most other European studies. The long-term renal outcome was better than previously reported and the prognosis appears to be favourable. Disclosures: None