Variations in the epidemiology of systemic lupus erythematosus in southern Sweden

Objective The epidemiology of systemic lupus erythematosus (SLE) within a defined region in southern Sweden was studied during the time period 1981-2006. Furthermore, whether the phenotypic expression of SLE changed during the study period was investigated. Methods Patients with suspected SLE were retrieved from diagnosis registries, hospital records and central laboratory databases. All new cases of SLE in this region were identified using validated retrieval methods and observed prospectively in a structured follow-up program. SLE disease manifestations, including classification criteria, were followed over time. Results A total of 174 cases were diagnosed with SLE during 1981-2006. In the first period of the study, from 1981 to 1993, the incidence of SLE was 5.0/100,000 inhabitants and in the second period of the study, 1994-2006, the annual incidence decreased to 2.8/100,000. During the first period the highest incidence was among females between the ages of 45 and 54 years; 15.1/100,000 inhabitants, which was reduced in the second period to 3.8/100,000. During the second period the highest age and sex specific incidence was among women between 25 and 34 years (6.6/100,000 inhabitants). The point prevalence of SLE on 31 December 1993 was 55/100,000 inhabitants compared with 31 December 2006, when it was 65/100,000 inhabitants. The phenotype of the disease did not vary significantly during the study period. Conclusion The incidence rate of SLE in younger females remained stable from 1981 to 2006. However, in middle-aged women the incidence was substantially reduced in the latter half of the study period.