[Diagnostic significance of C4d in membranous nephropathy].

Introduction: Membranous nephropathy (MN) is the most common cause of primary nephrotic syndrome in adults (20-30%). Light microscopy shows thickening of glomerular basement membrane with appearance of spikes. These histological findings are not evident in early forms, in which case the granular deposition pattern of IgG and/or C3 in the basement membrane by immunofluorescence (IF) constitutes the diagnostic tool that allows to differentiate it from minimal change disease (MCD). Complement system plays a key role in the pathophysiology of MN. C4d is a degradation product and a marker of the complement system activation. C4d labelling by immunohistochemical (HI) technique can help in the differential diagnosis between both glomerulopathies NM and MCD when the material for IF is insufficient and light microscopy is normal. Our objective was to explore the discrimination power of C4d to differentiate between MN and MCD in renal biopsy material.

Methods: Paraffin-embedded samples were recovered from renal biopsies with a diagnosis of MN and MCD performed between 1/1/2008 and 4/1/2019. IH staining was performed by immunoperoxidase technique using a rabbit anti-human C4d polyclonal antibody.

Results: In all cases with MN (n = 27, 15 males) with a median age of 63 (range: 18-87) years, C4d deposits were detected. In 21 cases with MCD (12 males) with a median age of 51 (range: 18-87) years, the C4d marking was negative in every samples.

Conclusion: The results indicate that the marking of the renal biopsy with C4d is a useful tool for the differential diagnosis between NM and MCD.