Gender differences in the incidence of systemic lupus erythematosus in Norway: a population-based cohort study. (September 2022)

• Record Type: Journal Article
• Authors: Haukeland, Hilde; Reppe Moe, Sigrid; Brunborg, Cathrine; Garen, Torhild; Botea, Antonela; Damjanic, Nenad; Wivestad, Gro; Ovreaas, Heidi; Boe, Thea; Orre, Anniken; Molberg, Oyvind; Lerang, Karoline
• Is Part Of: Lancet. Volume 4(2022)Supplement 1
• Page Start: S9
• Publication Date: 2022-09
• Subjects: Rheumatology -- periodicals; 616.72305
• DOI: 10.1016/S2665-9913(22)00288-0
• Languages: English
• ISSNs: 2665-9913

Abstract

Abstract: Background: Norway is one of the few countries worldwide where societal factors facilitate complete population-based cohorts on rare diseases. We aimed to estimate gender differences in the annual incidence of systemic lupus erythematosus in South-East Norway (population 2·9 million). Methods: This population-based cohort study was done using databases from 12 public hospitals in South-East Norway. We identified participants on the basis of a diagnosis with systemic lupus erythematosus (ICD-10 code M32), chart reviews, and recorded demographic and clinical parameters. Participants with clinical systemic lupus erythematosus who met the 1997 American College of Rheumatology (ACR) classification criteria were included. We looked for secular trends by dividing the cohort into two decades (1999–2007 and 2008–2017) and stratified by age and gender. We defined gender in accordance with the Norwegian social security number, which defines individuals as female or male. Time trend analysis was estimated using the χ 2 test. Findings: Between Jan 1, 1999, and Dec 31, 2017, records for 3490 individuals were extracted. 1558 (44·6%) of 3490 had a systemic lupus erythematosus diagnosis in their medical record. The 1997 ACR criteria were met by 1300 (83·4%) of 1558 people, and 673 (51·8%) of those 1300 were diagnosed between 1999–2017. The median age of participants was 38 years (IQR 25–49). The peak incidence rate was 4·3 per 100 000 women aged 20–29 years and 0·6 per 100 000 men aged 40–69 years. The average incidence rate of systemic lupus erythematosus in children and adolescents (defined as disease onset at age 15 years or younger) was stable at 0·3 for during 1999–2007 and 0·4 during 2008–2017. The average incidence rate for adult-onset systemic lupus erythematosus (defined as disease onset at age 16 years or older) in 1999–2017 was 1·6 per 100 000 people (2·7 per 100 000 women and 0·5 per 100 000 men). The incidence rate for 1999–2007 was 3·0 per 100 000 women and 0·6 per 100 000 men. The incidence rate in 2008–2017 was 2·4 per 100 000 women and 0·4 per 100 000 men. Women aged 50–59 years had a significant reduction in annual incidence from 3·0 per 100 000 during 1999–2007 to 1·3 per 100 000 during 2008–2017 (p=0·0007). The overall incidence rate for adults, children, and adolescents showed a significant decline during 1999–2017 from 1·85 to 1·13 per 100 000 (p=0·0036). The decline for women was from 3·08 to 2·13 per 100 000 (p=0·033) and for men was from 0·58 to 0·14 per 100 000 (p=0·033). Women aged 50–59 years also showed a significant decline in annual incidence during 1999–2017 from 3·39 to 1·07 per 100 000 women aged 50–59 years (p=0·0031). Interpretation: We found decreasing incidence of systemic lupus erythematosus during 1999–2017, which was most pronounced in women aged 50–59 years. This finding might be due to the reduction of hormone replacement therapy in this timeframe. Funding: The Norwegian Women's Public Health Association, The DAM Foundation, Vivi Irene Hansens Foundation, and the Norwegian Rheumatism Association.