Christina Frangou

San Diego—Bariatric surgery induces a significant and lasting improvement in diabetic nephropathy, with nearly 60% of patients with this condition achieving remission five years after surgery, according to a study presented at the 2012 annual meeting of the American Society for Metabolic and Bariatric Surgery.

The investigators say that the finding demonstrates a previously unknown microvascular effect of bariatric surgery.

“When we started this study, we thought bariatric surgery may just halt the progression of diabetic nephropathy. Instead, over half the patients who had diabetic nephropathy prior to undergoing bariatric surgery experienced remission,” said lead author Helen M. Heneghan, MD, a bariatric surgery fellow at Cleveland Clinic Bariatric and Metabolic Institute, in Ohio.

Dr. Heneghan said the finding warrants greater consideration of bariatric surgery in patients with diabetic kidney disease. However, she said, more studies with larger numbers of patients are still needed to confirm the results.

Dr. Heneghan and her colleagues examined the five-year outcomes of 52 diabetic patients who underwent bariatric surgery at the Cleveland Clinic. Of these patients, 75% were women. They had a mean age of 51.2 years (±10.1 years) and a preoperative body mass index of 49 kg/m2 (±8.7 kg/m2).

Before their operations, 37.6% of patients had diabetic nephropathy, as indicated by microalbuminuria (30-299 mg/g creatinine) or macroalbuminuria (>300 mg/g creatinine). After bariatric surgery, nephropathy resolved in 58.3% of the patients at a mean follow-up of 66 months.

Patients with microalbuminuria and those with macroalbuminuria experienced similar improvements in nephropathy. For patients with microalbuminuria, 42% remained stable five years after surgery and 58% had a regression of their nephropathy. Half of the patients with macroalbuminuria remained stable and half experienced regression. No patient with nephropathy worsened or required dialysis.

For patients with no evidence of diabetic nephropathy prior to bariatric surgery, 75% remained without nephropathy after five years whereas the remaining 25% progressed to microalbuminuria.

“No medical therapy has been as effective in achieving an effect of this magnitude on diabetic nephropathy,” said study co-author Philip R. Schauer, MD, professor of surgery and director of Cleveland Clinic Bariatric and Metabolic Institute.

Similar to previous studies, bariatric surgery’s effect on diabetes was strongly dependent on the amount of weight loss. The patients with the greatest weight loss had the best results in terms of diabetes improvement in this study.

Overall, diabetes resolved in 44% of patients, who averaged a mean weight loss of 92.3 pounds. One-third of patients experienced an improvement in their diabetes; these patients lost an average of 77.8 pounds. And patients who had no improvement in diabetes showed the least weight loss, an average of 27.5 pounds after five years. They also had the highest levels of HbA1c (glycosylated hemoglobin) five years after surgery at 7.9%, in contrast to 5.9% among those with resolved diabetes and 6.9% among those with improvements in diabetes.

The investigators found no preoperative differences in the mean urinary albumin levels between patients who were prescribed a renoprotective agent and those who were not. However, postoperatively, patients who were not on an angiotensin-converting enzyme inhibitor had lower levels of albuminuria (within normal range) compared with those who remained on a renoprotective agent (P=0.039).

“This probably reflects the fact that patients who had improvement of their diabetes and regression or non-progression of their nephropathy status also had a significant improvement or remission of hypertension, and were no longer prescribed an antihypertensive medication,” said Dr. Heneghan.

In a discussion following the presentation, several surgeons asked if the type of bariatric procedure influenced nephropathy outcomes. One surgeon suggested that the duodenal switch, with its high reported rates of resolution of diabetes and improvement in hemoglobin C1 levels, may offer the best chance of improving diabetic nephropathy.

However, the study was too small to detect any differences in diabetic nephropathy based on bariatric procedure and no patient underwent a duodenal switch in the study, said Dr. Heneghan. Sixty-nine percent of patients underwent gastric bypass, 3% had sleeve and the remainder underwent laparoscopic gastric banding.

Malabsorptive procedures were associated with a trend toward higher rates of remission of diabetes and nephropathy, although the difference from other procedures was not significant.

“This study would suggest that gastric bypass would probably be the most effective procedure,” said Dr. Heneghan. “In our institution, we recommend a gastric bypass in patients who have obesity-associated diabetes.”