A 66-year-old man presented with edema, which had developed over the previous month. The urinary sediment showed fatty casts (Panel A), with typical "Maltese crosses" under polarized light (Panel B), and was otherwise unremarkable, with no sign of nephritis. Laboratory evaluation revealed hypoalbuminemia (2.2 g of albumin per deciliter), hypercholesterolemia (369 mg of cholesterol per deciliter [9.5 mmol per liter]), and a serum creatinine level of 1.0 mg per deciliter (88 µmol per liter); a spot urine sample showed a protein-to-creatinine ratio of 13. A diagnosis of idiopathic membranous nephropathy was made on the basis of a renal biopsy and . . . Join discussion...