MPO-ANCA crescentic glomerulonephritis complicated by membranous nephropathy: MPO demonstrated in epimembranous deposits

An elderly woman presented with haematuria and proteinuria accompanied by elevated serum myeloperoxidase (MPO)-specific anti-neutrophil cytoplasmic antibodies (MPO-ANCA). A renal biopsy revealed mild mesangial proliferation with fibrocellular crescent formation and a membranous glomerular lesion. Immunofluorescence microscopy using FITC-labelled rabbit anti-human MPO antibodies revealed granular MPO deposition along the glomerular capillary walls (GCW) with a staining profile similar to that of glomerular IgG deposition. The one-year follow-up renal biopsy revealed minimal IgG and undetectable MPO deposition. Both MPO and MPO-ANCA might have been responsible for the IgG immune depositions along the GCW in this patient.