Occurrence of systemic lupus erythematosus in a Danish community: an 8‐year prospective study

Abstract

Objectives: To determine the prevalence and annual incidence of definite systemic lupus erythematosus (D‐SLE) and incomplete SLE (I‐SLE) in a community‐based lupus cohort of predominantly Nordic ancestry in an 8‐year prospective study from 1995 to 2003, and also to calculate the annual transition rate of I‐SLE to D‐SLE.Methods: In 1995 all SLE patients in the county of Funen were retrieved from four separate and independent sources. Incident cases were subsequently identified by surveillance of these sources.Results: During the 8‐year study period the median annual incidence of D‐SLE (1.04 per 100 000) and I‐SLE (0.36 per 100 000) remained almost constant. The point prevalence (PP) of D‐SLE increased from 21.9 to 28.3 per 100 000, and from 6.19 to 7.53 per 100 000 for I‐SLE. During follow‐up, seven I‐SLE patients transformed into D‐SLE at a progression rate of 3.64 per 100 person‐years at risk [95% confidence interval (CI) 1.44–7.55].Conclusions: Denmark is a low‐incidence lupus area but lupus prevalence is increasing slowly. I‐SLE is a disease variant that may eventually convert into D‐SLE.