POS-126 PROLIFERATIVE GLOMERULONEPHRITIS WITH MONOCLONAL IgG DEPOSITS;A NOVEL PATHOLOGIC PRESENTATION

ABSTRACT

Introduction: Proliferative glomerulonephritis with monoclonal IgG deposits (PGNMID) is a rare form of PGN that mimics immune-complex (IC) GN by light microscopy (LM), but shows monoclonal IgG deposits by immunofluorescence (IF). PGNMID often presents with membranoproliferative (MPGN) pattern or endocapillary hypercellularity. Focal crescents are not uncommon in PGNMID, but diffuse crescentic involvement is very rare. Methods: 78-year-old man with a history of hypertension and multiple cardiovascular comorbidities presented with weakness, dizziness, and anorexia, and was found to have severe hypertension and acute kidney injury with serum creatinine of 12 mg/dl (baseline 1 mg/dl). He was a chronic smoker and alcoholic. He reported productive cough with scanty whitish sputum, but denied hemoptysis. Urine analysis showed marked proteinuria, hematuria, and leukocyturia. Renal ultrasound revealed bilateral decrease corticomedullary differentiation without obstruction. Hemodialysis was initiated. Imaging showed bilateral upper lobe pneumonia with concerns for alveolar hemorrhages. Serology for complements, ANA, dsDNA, ANCA, Hepatitis B and C, Covid19 was negative. Kappa/lambda free light chain ratio was normal. SPEP, UPEP and immunofixation were negative for paraproteinemia. Renal biopsy showed diffuse crescentic and endocapillary PGN with MPGN features, and linear monoclonal IgG3-kappa immune deposits. Given the lack of clinical evidence of cryoglobulinemia and presence of immune-type electron dense deposits without organized substructures by EM, the findings were most consistent with PGNMID. However, the unusual biopsy presentation raised concerns for possible concurrent anti-GBM disease. Subsequently, Solu-Medrol was started followed by prednisone 1 mg/kg. He received 2 sessions of plasmapheresis before anti-GBM serology returned negative. Bone marrow biopsy revealed monoclonal B-cell lymphocytosis with CLL phenotype. Unfortunately, the patient developed Covid19 infection, and passed away before receiving further treatment. [Formula presented] Results: PGNMID is a rare form of renal involvement by monoclonal immunoglobulin deposition that mimics ICGN on renal biopsy. Nephrotic range proteinuria, hematuria and renal insufficiency are usual presentation. Cases of PGNMID classically show IgG3k, in a granular glomerular capillary wall, mesangial, and occasionally subepithelial distribution. By EM, these deposits appear granular typical of ICGN which lack organized substructure. The predominant LM patterns are MPGN and endocapillary hypercellularity. Less frequently focal crescents may be present, but diffuse crescentic involvement is especially rare (~5%). In our case, the diffuse cellular crescents and semilinear to linear GBM staining was unusual. Together with the clinical presentation, the findings prompted concerns for a concomitant Goodpasture syndrome, but anti-GBM antibody returned negative. The pathogenesis is still unclear, but some authors suggest infection as a possible trigger for crescentic transformation in PGNMID. The presence of crescents seem to confer a poorer prognosis and associated with progression to ESRD. Conclusions: Our case is a unique presentation of PGNMID in a patient who presented with clinical and pathologic features concerning for Goodpasture syndrome. PGNMID can rarely present with diffuse crescents and IF findings similar to anti-GBM nephritis in a patient with RPGN. No conflict of interest