Physicians monitoring patients who have undergone gastric bypass surgery should be on the alert for a new, potentially dangerous hypoglycemia complication that, while rare, may require quick treatment, according to a new study by collaborating researchers at Joslin Diabetes Center, Beth Israel Deaconess Medical Center, and Brigham and Women's Hospital.¹ About 160,000 people undergo gastric bypass surgery every year.

The study details the history of 3 patients, without diabetes, who, after gastric bypass surgery, suffered such severe hypoglycemia following meals that they became confused and sometimes blacked out, in 2 cases causing automobile collisions.

"Severe hypoglycemia is a complication of gastric bypass surgery and should be considered if the patient has symptoms such as confusion, lightheadedness, rapid heart rate, shaking, sweating, excessive hunger, bad headaches in the morning, or bad nightmares," says Mary-Elizabeth Patti, MD, investigator in Joslin's Research Section on Cellular and Molecular Physiology and Assistant Professor of Medicine at Harvard Medical School. "If these symptoms don't respond to simple changes in diet, such as restricting intake of simple carbohydrates, patients should be quickly evaluated hormonally," she adds.

The 3 patients—a woman in her 20s, another in her 60s, and a man in his 40s—all lost significant amounts of weight through gastric bypass surgery, putting them in the normal body mass index range. Each, however, developed postprandial hypoglycemia that failed to respond to dietary or medical intervention. As a result, all patients required removal of part or all of the pancreas. In all 3 cases, it was found that the insulin-producing islet cells had proliferated abnormally.

A potential cause of this severe hypoglycemia in these patients is "dumping syndrome," associated with a constellation of symptoms including palpitations, lightheadedness, abdominal cramping, and diarrhea, explains Dr Patti. Dumping syndrome occurs when the small intestine fills too quickly with undigested food passing from the stomach, as can happen following gastric bypass surgery. But the failure to respond to dietary and medical therapy and the worsening conditions over time suggested that additional pathology was the explanation of the symptoms' severity.

Other causes of postprandial hypoglycemia can include overactive islet cells, sometimes caused by excess numbers of cells, a tumor in the pancreas that produces too much insulin, or familial hyperinsulinism (hereditary production of too much insulin), which in severe cases can necessitate removal of the pancreas.

1. Patti ME, McMahon G, Mun EC, et al. Severe hypoglycaemia post-gastric bypass requiring partial pancreatectomy: evidence for inappropriate insulin secretion and pancreatic islet hyperplasia. Diabetologia. 2005;Sep 30; [Epub ahead of print].