Classification System for Diabetic Nephropathy May Advance Patient Care

The number of people with diabetes worldwide is 285 million and rising. The increasing incidence will result in more cases of DN, according to the authors.

"[DN] is a complex condition with varying degrees of severity and varying effects on the kidneys," write Jan Anthonie Bruijn, MD, PhD, from Leiden University Medical Center, the Netherlands, and colleagues. "Unlike other kidney conditions, [DN] has no standard classification system."

In 2006, experts from 16 universities formed an international team to develop a method for categorizing Type 1 and Type 2 DNs. Their goal was to differentiate associated lesions by prognostic severity in a standardized manner that could be easily translated into clinical practice around the world.

The physician group separated DN into 4 classes, based on biopsy findings. They range from the least severe (class 1) to the most severe (class 4):

• Class 1 -- glomerular basement membrane thickening: Biopsied material, which, under a light microscope, shows mild, nonspecific changes. No mesangial expansion, nodular increases in the mesangial matrix (Kimmelstiel-Wilson lesions), or global glomerulosclerosis of more than half of the glomeruli.
• Class 2 -- mesangial expansion, mild (2a) or severe (2b): Biopsies with any level of mesangial expansion that do not qualify for levels 3 or 4.
• Class 3 -- nodular sclerosis (Kimmelstiel-Wilson lesions): The presence of at least 1 strong Kimmelstiel-Wilson lesion but no more than 50% global glomerulosclerosis.
• Class 4 -- advanced diabetic glomerulosclerosis: Biopsies with more than 50% global glomerulosclerosis in which the damage is known to stem from DN.

The panel tested its DN categorization system in a pilot study. Five pathologists, working independently, assessed 25 biopsies, resulting in identical classifications in 18 cases. The overall outcome of the pilot was "satisfactory," according to the researchers, with an intraclass correlation coefficient of 0.84.

The classification system will help scientists discover more about the pathways of DN progression, and therefore improve patient care, the authors predict. They note that future research should focus on evaluating clinical results.

"An important question for every histologic classification system is whether it is predictive of clinical outcome," the authors write. "We feel validation should be done in separate prospective studies, preferably including protocol biopsies of patients with Type 1 and Type 2 diabetes and clearly defined clinical end points."