Rapidly progressive glomerulonephritis revealing the coexistence of diabetic nephropathy, membranous nephropathy, and MPO-ANCA-associated crescentic glomerulonephritis.

Diabetic nephropathy (DN) is the leading cause of chronic kidney disease worldwide. However, Patients with diabetes presenting with atypical renal manifestations may harbor superimposed non-diabetic kidney disease, making kidney biopsy essential for accurate diagnosis. Although cases of DN coexisting with either membranous nephropathy (MN) or MPO-ANCA-associated vasculitis have been reported, the concurrent occurrence of all three entities is exceptionally rare. We report the case of a 59-year-old man with a 20-year history of poorly controlled type 2 diabetes mellitus, diabetic retinopathy, hypertension, and chronic kidney disease attributed to DN, who presented with rapidly progressive kidney dysfunction. Serum creatinine increased from a baseline of ~ 220 to 560 μmol/L, accompanied by nephrotic-range proteinuria (9 g/day) and microscopic hematuria. Immunological testing demonstrated strongly positive MPO-ANCA (120 U/mL by ELISA), whereas PR3-ANCA, anti-glomerular basement membrane, antinuclear, and anti-phospholipase A2 receptor antibodies were negative. Kidney biopsy demonstrated nodular diabetic glomerulosclerosis, membranous nephropathy, and pauci-immune crescentic glomerulonephritis consistent with MPO-ANCA-associated vasculitis. Treatment with intravenous methylprednisolone, oral prednisone, and two 1-g infusions of rituximab resulted in partial recovery of kidney function, allowing discontinuation of temporary hemodialysis and stabilization of serum creatinine at ~ 300 μmol/L. This case highlights the indispensable role of kidney biopsy in diabetic patients with rapidly progressive kidney dysfunction and illustrates the diagnostic and therapeutic implications of identifying multiple coexisting glomerular diseases.