Epidemiology of patients with moderate-to-severe SLE in Sweden.

OBJECTIVE: SLE affects multiple organs and is associated with increased mortality and organ damage. While treatment recommendations for non-renal SLE stratify by disease activity, no standard approach to measuring severity exists. This study aimed to estimate the prevalence and incidence of SLE in Sweden, quantify patients with moderate-to-severe disease using register-based algorithms and examine associations between disease severity and survival. METHODS: We identified adult SLE patients in the Swedish National Patient Register with at least two SLE-coded visits between July 2005 and December 2019. Annual incidence and point prevalence were calculated. SLE patients were matched 5:1 with non-SLE comparators. SLE disease severity was classified annually postdiagnosis using an adapted algorithm based on prescriptions and comorbidities. Survival between SLE patients by each severity level in the year following diagnosis was compared with matched comparators using Cox regression models. RESULTS: In total, 10 186 SLE patients were identified, including 5076 incident cases. The average incidence of adult SLE in Sweden between 2015 and 2019 was 4.1 cases per 100 000, with a 2019 prevalence of 93.8 per 100 000. In the first year postdiagnosis, 61% of SLE patients had moderate-to-severe disease, stabilising at approximately 45% after 3-4 years among patients still in follow-up. Across all severity levels, SLE patients had poorer survival than comparators. High severity in the year following diagnosis was independently associated with increased mortality risk compared with mild disease, regardless of age, sex or prescribed treatments. CONCLUSIONS: Using national register data, the estimated prevalence of SLE in Sweden is higher than published figures from previous years. This is the first Swedish register-based study characterising SLE severity and its survival impact. Mortality risk is particularly increased in patients with moderate or severe SLE at diagnosis, underscoring the need for targeted strategies to improve outcomes for this group.