Abstract: SA-PO0746
Glomerular Histiocytosis with Monoclonal IgG Kappa Deposits: An Unusual Presentation of Monoclonal Gammopathy of Renal Significance
Session Information
- Glomerular Diseases: Lupus Nephritis, Monoclonal Gammopathy-Related Disease, and Transplantation
October 24, 2026 | Location: Exhibit Hall A, Convention Center
Abstract Time: 10:00 AM - 12:00 PM
Category: Glomerular Diseases
- 1402 Glomerular Diseases: Clinical, Outcomes, and Therapeutics
Authors
- Gomide Almeida, Guilherme, Washington University in St Louis, St. Louis, Missouri, United States
- Heady, Brittany, St Louis Kidney Consultants, St Louis, Missouri, United States
- Seltzer, Jay R., St Louis Kidney Consultants, St Louis, Missouri, United States
- Messias, Nidia Cordeiro, Washington University in St Louis, St. Louis, Missouri, United States
- Reisinger, Nathaniel, St Louis Kidney Consultants, St Louis, Missouri, United States
Introduction
Glomerular histiocytosis with non-crystalline monoclonal deposits is a rare, poorly characterized manifestation of monoclonal gammopathy of renal significance (MGRS).
Case Description
A 57-year-old man presented with hematuria, proteinuria (1.7 g), and creatinine of 0.9 mg/dL. He had a IgG kappa paraprotein and negative ANCAs. A kidney biopsy showed pauci-immune focal necrotizing crescentic GN with focal endocapillary hypercellularity. IF and EM were negative for deposits. He was given steroids, rituximab, and avacopan, but after 8 months UPCR had risen to 6 g/g and creatinine to 1.6 mg/dL. Repeat ANCA was negative. Re-biopsy showed proliferative GN with intracapillary histiocytes (CD68/CD163+), IgG kappa-restricted deposits on paraffin IF, and non-crystalline intracellular inclusions and electron dense deposits on electron microscopy. Bone marrow biopsy confirmed 5% kappa-restricted plasma cells. Dara-VCD was initiated.
Discussion
The initial diagnosis of pauci-immune crescentic GN hid the underlying MGRS given the absence of kappa restriction. The second biopsy showed diffuse proliferative GN with intracapillary histiocytic cells. Paraffin IF with IgG kappa restriction and IHC confirming histiocytes were pivotal in reclassifying the diagnosis and guiding clone-directed therapy. Few electron dense deposits and multiple atypical lysosomes were identified on EM. Glomerular histiocytosis with monoclonal deposits represents a diagnostic challenge. Repeat biopsy with full work up including paraffin IF should be considered when proteinuria progresses despite immunosuppression in the setting of monoclonal gammopathy. This case contributes to the limited literature on histiocytic glomerulopathy as a manifestation of paraprotein-mediated renal disease.
A. PAS 400x: mesangial and endocapillary hypercellularity, intracapillary histiocytes
B. Paraffin IF: granular capillary loop IgG kappa light chain restriction
C. EM: non-crystalline intracellular inclusions and electron dense deposits within histiocytes
D. IHC for CD163: confirms the presence of histiocytes