#2600 Idiopathic full-house non-lupus nephropathy
Authors: Roccatello Dario , Cozzi Martina , Terzolo Edoardo , Buzzurro Federica , Amore Giorgio , Fenoglio Roberta , Sciascia Savino 
Published: May 2024

Abstract

Background and Aims
A full-house pattern at immunofluorescence (IF) in kidney biopsies is usually associated with Lupus Nephritis (LN). However, it can be also secondary to other causes, such as infections, or it can idiopathic, without a defined origin. Idiopathic Full House non-lupus Nephropathy (iFH-N) represents a rare entity previously identified in small cohorts of patients, with different clinical features and outcomes. A limited number of the described cases developed overt systemic lupus erythematosus (SLE) during follow up, while renal outcome varied across different studies.
A retrospective observational study aimed at evaluating clinical presentation and outcomes of patients with iFH-N in a Tertiary Center has been performed. Long-term renal function and development of overt SLE have been considered as main outcomes of the study.

Method
All native kidney biopsies performed from January 2012 to December 2022 in our Institution were considered. Full-house pattern was defined as simultaneous positivity for IgG, IgM, IgA, C3 and C1q staining at IF. Inclusion criteria were: age ≥18, full-house pattern at kidney biopsy, patients not meeting criteria for SLE diagnosis according to American College of Rheumatology (ACR) 1997 classification or Systemic Lupus International Collaborating Clinics (SLICC) 2012 criteria. Exclusion criteria: diagnosis of SLE, secondary causes of full-house pattern at kidney biopsy.
We considered histological, clinical and laboratory features, performed therapies, renal function and SLE development during follow up.

Results
In the considered period, 2110 patients underwent a native kidney biopsy at our Institution. Of these, 91 patients had a histological finding of full-house nephropathy and were initially included for further evaluation. Of the 91 patients, 84 had received a diagnosis of SLE and were excluded, while 7 did not meet the criteria for a diagnosis of SLE. Two of these 7 were further excluded, having a full house pattern secondary to other conditions. Five patients were finally labelled as iFH-N. At kidney biopsy, all 5 included subjects had a Membranous Nephropathy, with extracapillary proliferation in 2 cases. They were all females, 4 Caucasians (80%), 1 Black (20%). At presentation, mean age was 28.2 years (range 21–40). All had impairment of kidney function, 2 of 5 had a full-blown nephrotic syndrome, 3 of 5 a nephrotic range proteinuria. Mean serum creatinine was 2.1 mg/dl (SD± 0.47), mean eGFR 35.2 ml/min/1.73 m2 (SD ±11), mean proteinuria 7.1 gr/24 h (SD ±3.3). Antinuclear antibodies (ANA) were negative in 4 of 5 patients; anti-dsDNA, anti-extractable nuclear antigens (ENAs) and antiphospholipid antibodies were negative in all subjects; slightly low C3 was present in 3 of 5 subjects. All patients received immunosuppressive therapy, including high dose intravenous (iv) steroids in association with cyclophosphamide (CYC) or mycophenolate mofetil, or Intensified B Cell Depletion Protocol (i.e. iv steroids + CYC and Rituximab). Mean follow-up from the time of kidney biopsy was 7.4 year (SD ± 2.4) (range 3–10 years). During follow up, 4 patients (80%) developed end stage renal disease (ESRD) needing renal replacement therapy, 3 of them within 24 months after presentation. The two patients with crescents had a severe prognosis, starting dialysis within 10 months after presentation. The fifth patient developed chronic kidney disease stage 4. One patient formally developed an ACR negative, SLICC positive SLE two years after presentation, with new positivity for ANA and anti-dsDNA antibodies at high titer and low C3, in addition to renal involvement.

Conclusion
All patients with iFH-N had similar presentation, being all young females, with a Membranous Nephropathy, nephrotic proteinuria and impairment of kidney function. They all had an aggressive form of kidney disease, refractory to different regimens of immunosuppression and with poor long-term renal outcome. Only one case developed SLE on the long term, although without systemic signs. The relationship between idiopathic full-house nephropathy and SLE remains controversial.