Purpose We examined variations in incidence and prevalence of systemic lupus erythematosus (SLE) within a geographically defined area of central Sweden over a time period of 14 years. We described longitudinal differences in disease activity measures (e.g., the SLE disease activity index-2000 [SLEDAI-2K] and the Physician’s Global Assessment), laboratory measurements and disease manifestations included among the American College of Rheumatology (ACR) criteria.
Methods We identified adults (≥18 years) residing in Östergötland County between 2008 and 2021 (mean adult population: 357 000 citizens) with a clinical diagnosis of SLE. Cases were defined as those with an SLE diagnosis set by a rheumatologist combined with fulfillment of the 1982 ACR classification criteria and/or the Fries’ diagnostic principle (presence of antinuclear antibodies [ANA] by immunofluorescence microscopy at least once plus involvement of at least two defined organ systems). All subjects were included in the quality and research register ’Clinical Lupus Register in North-Eastern Gothia’ (Swedish acronym KLURING). Individuals were followed prospectively until death, December 31, 2021, or emigration. We estimated incidence per 100 000 inhabitants stratified by sex and age. We used linear regression with calendar year of diagnosis as the outcome to assess whether each clinical measurement at diagnosis varied over time.
Results 126 new SLE cases (80% females) were diagnosed during the period 2008–2021, yielding a mean annual incidence of 3.0 per 100 000 inhabitants; higher in females (4.8 per 100 000) than in males (1.2 per 100 000). The mean age at diagnosis was 43.7 (Standard deviation [SD] 17.3) years (see Figure 1). Lupus nephritis was diagnosed in 36 of 126 (28.6%) at onset of SLE. The prevalence of SLE on December 31st 2021 was 64.5 per 100 000 inhabitants (87% females); higher in females (110.7 per 100 000) compared to males (17.4 per 100 000). The mean age was 55.9 (SD 16.7) years. Age at diagnosis and disease activity measures (SLEDAI-2K and the Physician’s Global Assessment) increased (p<0.05) over the time period, but none of the laboratory items changed significantly. Lupus nephritis, as well as involvement of other organ systems (e.g., fulfilled classification criteria), at disease onset did not vary significantly.
Conclusions In Östergötland County, SLE incidence and prevalence estimates were constant during the 14 years of follow-up. Whereas the prevalence of SLE was almost identical to what has previously been reported from Southern Sweden (Ståhl-Hallengren C, et al. J Rheumatol 2000;27:685–91; Ingvarsson RF, et al. Lupus 2016;25:772–80), we obtained slightly lower incidence figures. In addition, our data indicate that SLE is diagnosed also among older individuals with a more even female-to-male ratio. Disease phenotypes observed in patients at onset of SLE were similar over the time period.
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