Renal failure due to tubular obstruction by large protein casts in patients with massive proteinuria

We describe two patients with nephrotic syndrome whose histologic findings on renal biopsy and at autopsy are characterized by numerous large protein casts in dilated cortical tubules, as well as podocyte swelling with effacement of foot processes in the glomeruli. Both patients progressed rapidly to renal failure. The casts and the protein precipitate in the Bowman's capsule were found to be composed of varying proportions of albumin and globulin but contained no Tamm-Horsfall protein. This suggests a glomerular rather than tubular origin of proteins. Light and electron microscopic examination of tubules revealed changes mainly due to compression by the casts. We propose that tubular obstruction due to the large casts was the main cause of renal failure.