Abstract: SA-PO849
Novel Grid-Like Substructure in a Case of Paracrystalline Monoclonal Gammopathy of Renal Significance (MGRS)
Session Information
- C3G, TMA, MGRS, Amyloidosis, and More
October 26, 2024 | Location: Exhibit Hall, Convention Center
Abstract Time: 10:00 AM - 12:00 PM
Category: Glomerular Diseases
- 1402 Glomerular Diseases: Clinical, Outcomes, and Therapeutics
Authors
- Gupta, Rajib K., UC Davis Medical Center, Sacramento, California, United States
- George, Sajid Melvin, Richmond Nephrology Associates, Richmond, Virginia, United States
- Gu, Xin, LSU Health Shreveport, Shreveport, Louisiana, United States
- Arend, Lois J., Johns Hopkins University, Baltimore, Maryland, United States
Introduction
Monoclonal deposits with substructure in the kidney are essentially of 3 types – fibrillary, microtubular and crystalline deposits. Grid-like substructure, also known by other descriptors like mesh-like, lattice-like or striated muscle-like, has been described as a rare electron microscopic (EM) appearance of monoclonal deposits occurring in association with monoclonal gammopathy of renal significance (MGRS), most commonly involving the glomeruli. Here we describe a rare case with abundant grid-like monoclonal deposits.
Case Description
Patient is a 62-year-old Caucasian male with pancytopenia, acute kidney injury and a recent diagnosis of MGUS. SPEP showed a monoclonal M-spike 1.1 gm/dL with IgG kappa on serum and urine immunofixation. Bone marrow biopsy showed 5% kappa-restricted plasmacytosis, and a kappa to lambda ratio of 2.7. Serum complements were low. The patient also had motor neuropathy. Urinalysis showed 3+ protein and 3+ blood. Rheumatoid factor, serum cryoglobulin, ANCA and anti-GBM antibodies were negative. ANA was mildly positive. Kidney biopsy revealed glomeruli with a membranoproliferative pattern along with occlusive, large, intracapillary hypereosinophilic pseudothrombi which showed IgG1 and kappa restriction on immunofluorescence. EM revealed massive intraluminal and subendothelial electron-dense deposits having an extremely compact grid-like paracrystalline substructure, vaguely resembling the EM appearance of striated muscle.
Discussion
Grid-like substructure has been described in association with monoclonal renal disease in few reports, most typically type 1 cryoglobulinemic glomerulonephritis (CryoGN) although rare association with proliferative GN with monoclonal immunoglobulin deposits (PGNMID) has also been described. In this patient, the overall histologic findings favored a type 1 seronegative CryoGN. Awareness of such rare substructure and its association with monoclonal glomerular deposits is important for timely diagnosis of MGRS.