Patients with MN are at increased risk of renal vein thrombosis, even among other patients with nephrotic syndrome. This complication affects up to one in five patients in some series. In general, the heavier the proteinuria and lower the serum albumin, the higher the risk for thrombotic complications.

MN can only be diagnosed based on histopathologic findings. Thus in adults with unexplained nephrotic syndrome, renal biopsy must be performed. In MN, light microscopy reveals diffuse GBM thickening, which is especially prominent with silver stains. The pathogenetic immune complexes are not visible at this resolution; however, the growing GBM forms “spikes” between these complexes, which may be seen instead. In primary MN there are generally no cellular infiltrates, since the immune complexes form in the subepithelium and are thus protected from the circulation. In secondary MN, however, infiltrates may occur because circulating immune complexes also deposit in the mesangium.