A case of idiopathic membranoproliferative glomerulonephritis with a transient glomerular deposition of nephritis-associated plasmin receptor antigen

The differential diagnosis of acute poststreptococcal glomerulonephritis (APSGN) and idiopathic membranoproliferative glomerulonephritis (MPGN) is sometimes difficult, as they share several key features in their laboratory and histological findings, especially during the acute phase of the diseases. We herein report an idiopathic case of MPGN in which the glomerular deposition of nephritis-associated plasmin receptor (NAPlr), a recently identified nephritic antigen for APSGN, was demonstrated. A 24-year-old postpartum woman developed nephrotic syndrome and hypocomplementemia. Although she showed no apparent findings of a prior infection, her serum titer of antistreptolysin O antibody was elevated. Renal biopsies were performed twice at intervals of 6 months, both of which showed findings fully consistent with those of MPGN. Of note, fluorescent immunostaining for NAPlr was positive in the glomeruli of the first biopsy but not in the second. Despite the use of a corticosteroid, hypocomplementemia persisted for more than 1 year. It was therefore suggested that a streptococcal infection may have influenced the development of glomerular injury in this idiopathic case of MPGN.