Declining Incidence of Systemic Lupus Erythematosus in Norway 1999-2017: Data From a Population Cohort Identified by International Classification of Diseases, 10th Revision Code and Verified by Classification.

OBJECTIVE: The goal of this study was to provide complete, robust data on annual systemic lupus erythematosus (SLE) incidence rates over nearly two decades from the Southeast Norway area (2.9 million inhabitants) and assess accuracy of SLE-specific International Classification of Diseases (ICD) codes for SLE diagnosis. METHODS: From administrative databases, we identified all cases International Statistical Classification of Diseases and Related Health Problems, Tenth Revision (ICD-10) coded as SLE during 1999 through 2017 in Southeast Norway. We manually reviewed the chart of every case ICD-10 coded as SLE to either confirm or reject SLE diagnosis. Using SLE classification criteria, we classified all cases with confirmed SLE. We estimated annual incidence rates of classified SLE, and subsets, defined by age at diagnosis, sex, and parental country of birth. The chi-square test was applied for linear time-trend analyses of incidence. RESULTS: Among the 3,488 cases ICD-10 coded as SLE, chart reviews confirmed SLE diagnosis in 1,558 (45%), of which 797 had new-onset disease during 1999 through 2017. Annual SLE incidence rates fell during 1999 to 2017. The fall was most pronounced in female persons 50 to 59 years old at diagnosis, in whom incidence fell from 3.4 to 1.1 per 100,000 persons (P trend < 0.001). Concurrent ecological data from the study area showed a 74% reduction in prescriptions of menopausal hormone treatment. Accuracy of ICD-10 codes for incident SLE diagnosis was acceptable in juveniles and young adults (up to 20 years) but otherwise low. CONCLUSION: In a presumably complete population-based cohort, we identified decreasing incidence of SLE, especially among female persons 50 to 59 years old. Although reasons for declining incidence are not clear, ecological data indicate a possible role of environmental factors, for example, menopausal hormone treatments.

Persisting mortality gap in systemic lupus erythematosus; a population-based study on juvenile- and adult-onset SLE in Norway 1999-2022.

OBJECTIVE: To estimate mortality and survival rates of systemic lupus erythematosus (SLE) in a contemporary, population-based setting and assess potential influences by time, sex, ethnicity, classification criteria and age at diagnosis. METHODS: We assessed mortality and survival in the Nor-SLE cohort, which includes all chart-review confirmed SLE cases resident in Southeast Norway (population 2.9 million) 1999-2017. Study end was at death, emigration, or 1 October 2022. We defined juvenile SLE by age <16 years at diagnosis. For standardized mortality rate (SMR) estimates, we applied 15 population controls per case, all matched for age, sex, residency, and ethnicity. We analyzed survival by Kaplan-Meier and risk factors by cox regression. RESULTS: The Nor-SLE cohort included 1558 SLE cases, of whom 749 were incident and met the 2019 European Alliance of Associations for Rheumatology and American College of Rheumatology (2019-EA) classification criteria. SMR was increased to 1.8 (95% CI 1.6-2.2) in incident adult-onset SLE but did not differ between females and males. Survival rates at 5-, 10-, 15 and 20-years were lower in incident adult-onset SLE than in matched controls. In multivariable analysis, lupus nephritis associated with decreased survival, while sex did not. Separate, long-term mortality analyses in the total Nor-SLE cohort showed that SMR peaked at 7.2 (95% CI 3.3-14) in juvenile-onset SLE (n = 93) and fell gradually by increasing age at SLE diagnosis. CONCLUSION: This study shows persistence of a mortality gap between adult-onset SLE and controls at population level and provides indications of worryingly high mortality in juvenile-onset SLE.