New interpretation of diabetic nephropathy or diabetic kidney disease from kidney biopsy: review article

Many nephrologists considered that renal involvement in diabetes patients was seen as nodular glomerulosclerosis (i.e., Kimmelstiel-Wilson lesions). However, they diagnosed diabetic nephropathy or diabetic kidney disease (DKD) from clinical information on diabetes history, and reports of evaluation by kidney biopsy were scarce. Since the publication of the Tervaert classification of diabetic nephropathy in 2010, reports of kidney biopsy in these patients have increased. Analysis of biopsy specimens revealed not only the Tervaert classification (class I to IV) based on glomerular lesions, but also various other pathologies. Besides nodular lesions, findings included paratubular basement membrane insudative lesions (PTBMILs), polar vasculosis, and nephropathy associated with novel drugs (sodium-glucose transport protein 2 inhibitors and dipeptidyl peptidase-4 inhibitors). PTBMILs are unique to diabetic nephropathy. In patients with continuous hyperglycemia and excessive salt intake, elevated blood osmolality (calculated by serum Na × 2 + serum glucose/18 + serum urea nitrogen/2.8) leads to thirst and excessive drinking, which results in fluid overload and generalized edema. The increase in circulating blood volume is thought to induce PTBMILs because of the influx of serum components into the endothelium of glomerular vessels. This case series review presents diverse kidney biopsy findings in patients with diabetic nephropathy or diabetic kidney disease as well as the pathogenesis.