A man in his early 60s was being treated for metastatic adenocarcinoma of the lung for 2 years. Recently, he had been complaining of increasing hemoptysis and a PET CT was performed which showed progression of his disease. He presented to the ED with general malaise, edema and abdominal bloating. His creatinine had increased from a baseline of 1.0 to 1.5mg/dl and he had >10g urinary protein daily. A renal biopsy was performed. Light microscopy revealed thickened basement membranes with some double-contour formation but no definite “spikes” Immunofluorescence showed dense granular staining for IgG along the capillary loops with some minor staining in the mesangium. The diagnosis was early secondary membranous glomerulopathy most likely related to the progression of his malignancy. An EM image is shown below (Click to enlarge)
Subepithelial deposits typical of membranous nephropathy are easily seen in the image (A). The overlying podocytes are damaged and the foot processes are effaced. The lower part of the image (B) shows an area at the junction of the capillary loop and the mesangium. Here, a deposit is also present but it appears that the overlying glomerular epithelium degenerated and is sloughing into the lumen. This is likely due to complement activation and the formation of membrane attack complexes induced by the presence of the deposits and is thought to be the cause of the severe proteinuria seen in this patient. It is important to note that this is not associated with inflammation because the complexes are out of the reach of inflammatory cells which is not the case where subendothelial deposits predominate. This case was not entirely typical because there were occasional subendothelial deposits noted throughout the glomerulus although they were few and their significance was uncertain.
Thanks to Dr Bijol for the Image