Immunoglobulin M nephropathy in a patient with systemic lupus.

Immunoglobulin M (IgM) nephropathy is an uncommon glomerular disease characterized by IgM deposits in the mesangium. This case report describes a 52-year-old woman with a 10-year history of underlying systemic lupus erythematosus with minimal proteinuria who developed sudden onset of nephrotic syndrome. Renal biopsy revealed IgM nephropathy, with no clear evidence of lupus nephritis. Complements and dsDNA serologies were negative. The nephrotic syndrome resolved with prednisone therapy. Four months later, while receiving a maintenance dose of prednisone, the proteinuria relapsed. Remission was achieved after a repeat course of steroid therapy. Low-dose prednisone therapy was maintained thereafter for long-standing steroid-dependent lupus.