Late-Onset Lupus Nephritis: Clinical-Epidemiological, Histological, Prognostic, and Therapeutic Implications: A Single-Center Experience from Northeastern Spain.

Introduction: Systemic lupus erythematosus (SLE), as an autoimmune disease, and lupus nephritis (LN), are typically diagnosed in women at fertile age. Late-onset SLE is defined as a disease onset over 45-50 years. Our main objective was to analyze the clinical, histological, prognostic, and therapeutic features related to LN in our late-onset SLE population. Methods: A single-center and retrospective study was performed comparing clinical-demographic, histological, prognostic, and therapeutic features of 45 LN patients from 1994 to 2023. We divided the study population according to the age of onset of LN into classic onset (<45 years) and late onset (≥45 years). Results: Late-onset LN patients showed a higher association with Sjögren's and antiphospholipid syndrome, more cardiovascular comorbidities at presentation, poorer renal function at diagnosis, and higher Systemic Lupus Damage Index (SDI) score. Histology showed more nonproliferative LN classes (II and V). Late-onset LN responders, compared to those with classic onset, achieved response later. Nonresponsive patients had a higher incidence of acute kidney injury (AKI), more glomerulosclerosis and interstitial fibrosis-tubular atrophy (IFTA) at presentation, and a higher frequency for renal replacement therapy (RRT) at diagnosis and during follow-up. The main independent variables associated with relapse were younger age at SLE diagnosis and initial partial renal response (PRR). Conclusions: Late-onset LN is often accompanied by other systemic autoimmune diseases such as Sjögren's and antiphospholipid syndrome. These patients have major cardiovascular comorbidities, poor estimated glomerular filtration rate (eGFR) at diagnosis, and increased chronicity index in histology. A tailored approach in this fragile population in order to avoid unnecessary immunosuppression is of critical interest.