Assessing the relative impact of lupus nephritis on mortality in a population-based systemic lupus erythematosus cohort

Objective There is limited knowledge on the relative impact of lupus nephritis (LN) on morbidity and mortality in population-based systemic lupus erythematous (SLE) cohorts. Here, the primary aim was to compare mortality rates between patients with and without LN in a population-based SLE cohort. Methods The study cohort included all SLE patients resident in the city of Oslo during 1999-2008. Follow-up time was median 14 (0-15) years. Presence of LN was defined according to the 1987 American College of Rheumatology classification criteria for SLE. LN class was determined by renal biopsy. Data on kidney function, including presence of end-stage renal disease (ESRD), were obtained from patient charts. Standardized mortality ratios (SMRs) were estimated by comparing deaths in the SLE cohort with age- and gender-matched population controls. Results We found that 98/325 SLE patients (30%) developed LN, 92% of whom had occurrence within the first five years from disease onset. Incidence rate of ESRD was 2.3 per 1000 patient-years. A total of 56 deaths occurred during the study period, corresponding to an overall SMR in the SLE cohort of 2.1 (95% confidence interval (CI) 1.2-3.4). Estimated SMR for LN patients was 3.8 (95% CI 2.1-6.2), and for SLE patients without LN it was 1.7 (95% CI 0.9-2.7). Conclusion In this population-based SLE cohort, we found that LN was associated with increased morbidity and mortality, whereas SLE patients who did not develop LN had good overall prognoses regarding survival.