Crystal-Induced Podocytopathy Producing Collapsing Focal Segmental Glomerulosclerosis in Monoclonal Gammopathy of Renal Significance: A Case Report

ABSTRACT Monoclonal gammopathy-associated crystalline podocytopathy causing collapsing focal segmental glomerulosclerosis (FSGS) is very rare and has been associated with pamidronate therapy. We present the case of a 53-year-old man with vision loss secondary to corneal crystals deposition, nephrotic-range proteinuria, and reduced glomerular filtration rate without associated comorbid conditions. Two kidney biopsies were initially reported as primary FSGS, but the patient did not respond to high dose corticosteroids immunosuppression therapy. Re-review of biopsies with additional electron microscopy analysis revealed crystalline inclusions in podocytes leading to collapsing FSGS. Subsequent work up revealed an IgG kappa serum monoclonal protein. Bone marrow biopsy revealed 5%-kappa restricted plasma cells with cytoplasmic crystalline inclusions. To our knowledge, this is the first case of monoclonal gammopathy of clinical significance manifesting as crystalline podocytopathy leading to collapsing FSGS and keratopathy leading to vision loss. Crystalline podocytopathy should be considered in the differential diagnosis of collapsing glomerulopathy, and careful ultrastructural examination of kidney biopsy is crucial to establish this diagnosis.