Delayed onset of systemic lupus erythematosus in patients with idiopathic membranous nephropathy

ObjectiveMembranous nephropathy can be categorised into idiopathic membranous nephropathy (iMN) and secondary membranous nephropathy (sMN). However, it should be noted that a subset of patients initially diagnosed with iMN may develop secondary etiologies during longitudinal follow-up, even in the absence of systemic manifestations at initial presentation.MethodsThis is a single-center retrospective analysis. From January 2017 to April 2024, patients who were diagnosed with iMN at the time of their initial renal biopsy, had no extrarenal lupus manifestations at that time, and subsequently developed lupus nephritis (LN) or systemic lupus erythematosus (SLE) during the follow-up period at our center were included. Patients with sMN and incomplete SLE at the time of the initial renal biopsy were excluded from the study.ResultsA total of six patients were included. Of these, five were female and one was male. The mean age of the patients was 30.00 ± 10.39 years. At the initial renal biopsy, the proteinuria level was 6.45 ± 1.83 g/L, the serum albumin level was 21.77 ± 3.69 g/L, and the estimated glomerular filtration rate was within the normal range. Notably, one patient exhibited a positive test result for the PLA2R antibody, with a titer of 135.5 RU/ml. Following the administration of immunotherapy, all six patients achieved remission. However, after a follow-up period of 7.00 ± 5.21 years, five of the patients experienced a recurrence. Repeat renal biopsies in four relapsed patients confirmed histopathological progression to LN (class Ⅲ+Ⅴ in two cases, class V in two cases). Two patients subsequently fulfilled the 2019 EULAR/ACR SLE classification criteria.ConclusionThe diagnosis of membranous nephropathy does not entirely exclude the possibility of secondary nephropathy, even in patients with a high PLA2R antibody titer. Consequently, close longitudinal follow-up for occult autoimmune disease remains a necessity in clinical practice.