Changing trends in presentation and indications of biopsy in lupus nephritis: data from the Spanish Registry of Glomerulonephritis.

Background: With the ageing population and changes in the indications of diagnostic and protocol biopsies in systemic lupus erythematosus in recent years, an impact on the incidence and presentation of lupus nephritis (LN) is expected. The aim of this study was to analyse the epidemiological changes regarding clinical and histological presentation of LN in kidney biopsies performed from 1994 to 2019 included in the Spanish Registry of Glomerulonephritis. Methods: We analysed data from 28 791 kidney biopsies from 130 Spanish hospitals comparing demographic, clinical and histological data. We divided the cohort according to the age of onset of LN into pediatric onset (<18 years), adult onset (18-50 years) and late onset (>50 years). Results: The incidence of LN has decreased from 9.6% of all kidney biopsies in the period 1994-2013 to 7% in the last quarter of the observation period (2014-2019) (P < 0.001), despite an increase in the proportion of patients with LN that underwent repeat biopsies (16.6-24%; P < 0.001). The age of onset of LN has increased from 32 ± 14 to 38 ± 14 years (P < 0.001), with an increase in the proportion of late-onset LN (from 13% to 22% of incident LN; P < 0.001). There were no differences in the distribution of histological features at presentation over the study period. Patients with late-onset LN showed fewer gender differences, had lower GFR and presented with less-proliferative forms of LN compared with early-onset LN. Conclusions: The frequency of biopsy-proven LN has been decreasing in recent years, despite an increasing number of repeat biopsies. Late-onset LN is increasing, presenting with worse kidney function but fewer proliferative lesions compared with younger-onset LN.