Incidence studies of systemic lupus erythematosus in Southern Sweden: increasing age, decreasing frequency of renal manifestations and good prognosis.

OBJECTIVE: To identify all new cases of systemic lupus erythematosus (SLE) within a defined area in Southern Sweden with validated methods of retrieval, and to compare 2 cohorts assembled during 1981-86 and 1987-91.
METHODS: The catchment area, the health care district of Lund-Orup, had during 1981-91 a mean adult population (> 15 years of age) of 172,300 individuals. During 1987-91 we identified 379 individuals with potential SLE diagnosis from diagnosis registers and from central laboratory databases. Out of these, 121 had a previously known SLE diagnosis. All patient records were reviewed and patients with possible SLE not already known at the SLE unit were invited and examined. Organ damage was recorded as the Systemic Lupus International Collaborating Clinics/American College of Rheumatology (SLICC/ACR) damage index.
RESULTS: Forty-one new SLE cases were diagnosed during 1987-91, giving a median annual incidence of 4.8/100,000 inhabitants, with a median age at diagnosis of 47 years. The incidence is similar to that found 1981-86 (4.5/100,000/year) in the same population using the same methods for retrieval. Age and sex-specific incidence 1981-91 was notably highest at the age of 65-74 (14.1/100,000/year) in women and age 65-74 (3.2/100,000/year) in men. The point prevalence on December 31, 1986, was a 42/100,000 and on December 31, 1991, 68/100,000. The 5 year survival was 93% and 10 year survival 83%. While overall survival was not decreased, 10 year survival was slightly reduced compared with an age and sex matched healthy population (p = 0.03). In the 1987-91 cohort the sensitivity of the American Rheumatism Association criteria was 92.7% and the specificity was 94%. The frequency of renal manifestations was decreased in the latter cohort. The damage rate was highest during the first year and then constant during a 5 year followup, and was similar in the 2 cohorts. Damage that related to atherosclerosis was common and cardiovascular disease was the most common cause of death.
CONCLUSION: The incidence of SLE in Sweden was notably constant during the 11 years 1981-91. Mortality was low and only late mortality (> 10 years disease duration) exceeded that in an age and sex matched control population. Atherosclerosis was the main cause of damage and mortality. Specificity and sensitivity of the ACR classification criteria are high in this epidemiologically recruited cohort.