Type 1 Cryoglobulinemic Glomerulonephritis With IgG2-Kappa Arising From Monoclonal Gammopathy of Undetermined Significance: A Case Report and Literature Review.

This case report describes a rare presentation of Type 1 Cryoglobulinemic Glomerulonephritis due to IgG2 kappa monoclonal gammopathy in a 74-year-old man with a history of Monoclonal Gammopathy of Undetermined Significance (MGUS), classifiable under Monoclonal Gammopathy of Renal Significance (MGRS). The patient presented with acute kidney injury, hypertensive urgency, and a migratory rash. Kidney biopsy revealed glomerulitis with IgG2-kappa deposition. Pseudothrombi of IgG2-kappa paraprotein were also present within glomerular capillary and arteriolar lumens, accompanied by vasculitis. Although initial outpatient management focused on MGUS, rapid disease progression necessitated aggressive therapy, including high-dose corticosteroids, plasmapheresis, and hemodialysis. The patient's renal function improved following treatment, emphasizing the need for early recognition and timely intervention in cryoglobulinemia-related kidney disease. This case highlights the importance of kidney biopsy in diagnosing MGRS and underscores the role of targeted therapies in complex cases, particularly clone-directed treatment following initial clinical stabilization.