The incidence of systemic lupus erythematosus (SLE) increased nearly twofold between 1976 and 2018 in a county in the Midwestern US. This increase may be partially explained by rising ethnic and racial diversity, according to a study published in Annals of Rheumatic Diseases.
Past estimates of the incidence of SLE in the US have yielded inconsistent results. The researchers measured the SLE incidence, prevalence, severity at diagnosis, and survival rates over 4 decades in Olmstead County, Minnesota.
Adult patients with SLE were identified using the Lupus Midwest Network. Demographic and clinical data were abstracted through medical record review. Incidence of SLE was calculated during the study period from 1976 to 2018 for the entire study population, and between 1999 and 2018 for non-Hispanic White and racial and ethnic minority populations. Point prevalence was estimated as the number of SLE cases on January 1 in 1985, 1995, 2005, and 2015. Severity of SLE was measured using the European Alliance of Associations for Rheumatology (EULAR)/American College of Rheumatology (ACR) score within 1 year of diagnosis. The standardized mortality ratio was estimated as the ratio of observed deaths in the SLE cohort to expected number of deaths based on the Minnesota population.
Between 1976 and 2018, there were 188 new cases of SLE (83% women). The mean age at diagnosis was 46.3±16.9 years. The overall age-adjusted and sex-adjusted incidence of SLE was 4.77 per 100,000 (95% CI, 4.09-5.46). Women had a higher incidence of SLE than men (7.58 per 100,000 vs 1.89 per 100,000, respectively). The incidence increased from 3.32 per 100,000 from 1976 to 1988 to 6.44 per 100,000 from 2009 to 2018, an increase of 2% per year. The severity of SLE did not change during the study period.
The overall incidence rate of SLE between 1999 and 2018 was 5.42 per 100,000 for the non-Hispanic White population vs 8.17 per 100,000 among racial and ethnic minority populations.
The prevalence of SLE increased from 30.6 (95% CI, 18.9-42.4) in 1985 to 97.4 (95% CI, 81.6-113.2) in 2015. The standardized mortality ratio of patients with SLE compared with the general population was 2.2 (95% CI, 1.6-3.0). This ratio did not change significantly over time.
Limitations of the study included the retrospective study design, a lack of antiphospholipid antibody data (which contributed to the EULAR/ACR score) prior to the 1980s, omission of ANA negative-lupus cases, the narrow geographic area, and a lack of power to detect trends in mortality.
The study authors concluded, “This population-based study showed that in this [US] population the incidence and prevalence of SLE is increasing. The increase in incidence may be at least partially explained by the increased ethnic and racial diversity in the population. The survival gap between SLE and the general population remains unchanged. As the [US] population grows more diverse, we might continue to see an increase in the incidence of SLE.”
Duarte-García A, Hocaoglu M, Valenzuela-Almada M, et al. Rising incidence and prevalence of systemic lupus erythematosus: a population-based study over four decades. Ann Rheum Dis. Published May 16, 2022. doi:10.1136/annrheumdis-2022-222276