Proliferative glomerulonephritis with monoclonal immunoglobulin deposits masquerading as renal-specific thrombotic microangiopathy

Proliferative glomerulonephritis with monoclonal immunoglobulin deposits is a form of monoclonal gammopathy of renal significance that can rarely co-occur with thrombotic microangiopathy (TMA). We report a rare case in a patient who presented with nephrotic syndrome, in whom the renal biopsy showed TMA and underlying granular electron-dense deposits predominantly along the subendothelial aspect of the glomerular basement membrane and mesangium. Immunofluorescence performed on proteinase-digested formalin-fixed, paraffin-embedded sections showed IgG3 kappa light chain restriction. Further clinical, radiologic and haematologic investigations showed no evidence of any underlying neoplastic B-cell or plasma cell clone. Following multidisciplinary team input, the patient was treated with bortezomib and plasma exchange, allowing long-term clinical stabilisation.