1. HYPOGLYCEMIA FOLLOWING GASTRIC SURGERY
Hypoglycemia sometimes develops in patients who have undergone gastric surgery (eg, gastrectomy, vagotomy, pyloroplasty, gastrojejunostomy, Nissan fundoplication, Billroth II procedure, and Roux-en-Y), especially when they consume foods containing high levels of readily absorbable carbohydrates. This late dumping syndrome occurs about 1–3 hours after a meal and is a result of rapid delivery of high concentration of carbohydrates in the proximal small bowel and rapid absorption of glucose. The hyperinsulinemic response to the high carbohydrate load causes hypoglycemia. Excessive release of gastrointestinal hormones such as GLP-1 likely play a role in the hyperinsulinemic response. The symptoms include lightheadedness, sweating, confusion and even loss of consciousness after eating a high carbohydrate meal. To document hypoglycemia, the patient should consume a meal that leads to symptoms during everyday life. An oral glucose tolerance test is not recommended because many normal persons have false-positive test results. There have been case reports of insulinoma and noninsulinoma pancreatogenous hypoglycemia syndrome in patients with hypoglycemia post Roux-en-Y surgery. It is unclear how often this occurs. A careful history may identify patients who have a history of hypoglycemia with exercise or missed meals, and these individuals may require a formal 72-hour fast to rule out an insulinoma.
Treatment for secondary dumping includes dietary modification, but this may be difficult to sustain. Patients can try more frequent meals with smaller portions of less rapidly digested carbohydrates. Alpha-glucosidase therapy may be a useful adjunct to a low carbohydrate diet. Octreotide 50 mcg administered subcutaneously two or three times a day 30 minutes prior to each meal has been reported to improve symptoms due to late dumping syndrome. Treatment with exendin 9-39, a GLP-1 receptor agonist, may prevent post gastric bypass hypoglycemia. SGLT2 inhibitors may ameliorate the postprandial glucose rise, the subsequent insulin response, and hypoglycemia. There is a report of a patient with Roux-en-Y surgery who had complete resolution of both hyperglycemia and hypoglycemia when she was given canagliflozin. Various surgical procedures to delay gastric emptying have been reported to improve symptoms but long-term efficacy studies are lacking.
2. FUNCTIONAL ALIMENTARY HYPOGLYCEMIA
Patients have symptoms suggestive of increased sympathetic activity, including anxiety, weakness, tremor, sweating or palpitations after meals. Physical examination and laboratory tests are normal. Previously, many of these patients underwent a 5-hour oral glucose tolerance test and the detection of glucose levels in the 50–60 mg/dL (2.8–3.3 mmol/L) range was thought to be responsible for the symptoms; the recommended treatment was dietary modification. It is now recognized that at least 10% of normal patients who do not have any symptoms have nadir glucose levels less than 50 mg/dL (2.8 mmol/L) during a 4- to 6-hour oral glucose tolerance test. In a study comparing responses to oral glucose tolerance test with a mixed meal tolerance test, none of the patients who had plasma glucose levels less than 50 mg/dL on oral glucose had low glucose ...