Lupus or not? Idiopathic full house glomerulonephritis: a rare nephropathy with unexpectedly severe outcome.

Objectives: A full-house pattern at immunofluorescence in kidney biopsies is usually associated with lupus nephritis. The cases that do not meet criteria for diagnosis of systemic lupus erythematosus (SLE) and have no secondary causes are classified as idiopathic full house (non-Lupus) nephropathy (iFH-N), which is a poorly defined entity. We aimed to evaluate the clinical presentation, renal outcome and development of SLE in the long term.

Methods: We carried out a retrospective observational study from 2012 to 2022 on patients with iFH-N, i.e. having a full-house pattern at immunofluorescence, but not meeting the criteria for the diagnosis of SLE and without a secondary cause.

Results: Of 2210 patients, 91 presented with full-house pattern at immunofluorescence: 84 had the criteria for SLE diagnosis, 2 had secondary causes, 5 were idiopathic. iFH-N cases were all young females with histological pattern of membranous nephropathy and impaired kidney function, at presentation two had a nephrotic syndrome, three a nephrotic range proteinuria. Mean serum creatinine was 2.1 mg/dl (SD± 0.47), mean eGFR 35.2 ml/min/1.73m2 (SD±11), mean proteinuria 7.1 gr/24h (SD±3.2). Four had negative antinuclear antibodies; none had anti-dsDNA, anti-extractable nuclear antigens, antiphospholipid antibodies; three had low C3 levels. All received aggressive immunosuppression (IS), including steroids, cyclophosphamide, mycophenolate mofetil or Intensified B Cell Depletion Protocol. Mean follow-up was 7.4 year (SD ± 2.4). Four patients (80%) developed end stage renal disease, three within 24 months, one patient chronic kidney disease stage 4. One subject developed SLE after two years.

Conclusions: All patients with iFH-N had similar clinical presentation, appeared to be refractory to aggressive IS, and had poor renal outcome.