Don't Be Fooled by the Full House

Introduction: Lupus nephritis (LN) is a common and serious systemic lupus erythematosus (SLE) complication. Some patients exhibit histological features of LN, characterized by the "full house" pattern on immunofluorescence (IF), despite the absence of other criteria for SLE. This rare entity is referred to as non-lupus full-house nephropathy (FHN). Herein, we present a rare case of non-lupus FHN in a kidney transplant recipient. Case Description: A 37-year-old female with a history of type 1 diabetes and ESRD s/p simultaneous pancreas-kidney transplant in 2004, and recurrent ascites presented with abdominal pain and was found to have cardiac tamponade with pericardial fluid negative for infection and malignancy. Her creatinine levels had increased for months, from 1.9 to 3 mg/dl with 2.2 g proteinuria and bland urine sediment. She had a functioning pancreas. The initial ANA test was 1:160 positive but repeated ANA and dsDNA were negative. Renal graft biopsy revealed membranoproliferative glomerulonephritis (MPGN) with a "full-house" linear pattern on IF and 60% IFTA. Concerned about de novo LN, she was treated with pulse steroid. However, there was no clinical response, and she returned to dialysis. Electron microscopy (EM) results came back later, which did not reveal any immune-type deposits. After a multidisciplinary discussion with pathologists and rheumatologists, the positive IF was interpreted as a nonspecific accumulation of serum protein constituents due to chronic endothelial and membranoproliferative injury associated with transplant glomerulopathy rather than true immune complex (IC) deposition disease. Discussion: This case presents a diagnostic challenge in distinguishing between de novo LN and non-lupus FHN secondary to transplant glomerulopathy. The combination of pericardial effusion, ascites, an initial ANA of 1:160, and a renal biopsy with full-house features could classify her as having SLE. However, this diagnosis relied heavily on the kidney biopsy interpretation. The development of lupus in a chronically immunosuppressed patient is unusual. Considering the absence of IC and the alternative diagnosis of transplant glomerulopathy, her presentation is not compatible with SLE and can be explained by other factors such as volume overload. This case underscores the importance of EM in diagnosing LN, highlighting that a full-house pattern does not necessarily indicate LN or immune complex deposition disease.