Hyperinsulinaemic-hypoglycaemia has been described following Roux-en-Y gastric bypass for obesity and is thought to be due to hyperfunction of pancreatic β cells. It has been questioned whether the β cell hyperfunction may have preceded the bariatric surgery and contributed to the obesity. We report a case of hyperinsulinaemic-hypoglycaemia in a non-diabetic, lean patient (BMI 26 kg/m2) who underwent distal gastrectomy and Roux-en-Y bypass for a benign gastric tumour. The 39 year-old male described neuroglycopenic symptoms occurring after food but not relieved by eating. Hypoglycaemia was confirmed on continuous capillary blood glucose monitoring. A 72-hour fast did not lead to hypoglycaemia. Prolonged 75 g oral glucose tolerance test resulted in prolonged hypoglycaemia between 90 and 210 minutes (glucose between 2.03.2 mmol/l). Insulin at that time ranged between 8.2 and 39 mU/l, GLP-1 peaked at 1025 pmol/l and C-peptide 12083310 nmol/l. Sulphonylurea screen was negative. A diagnosis of hyperinsulinaeic hypoglycaemia was made. The diagnosis of a GLP-1 secreting tumour was considered but was ruled out due to the absence of a lesion on CT imaging The patient was treated with a variety of medical therapies with a varying degree of success. He was given dietary advice to try to maintain a low glycaemic index and low carbohydrate diet. Guar gum, octreotide and verapamil all failed to control his hypoglycaemic episodes. Diazoxide was commenced and titrated up to an effective dose. No hypoglycaemia occurred whilst on diazoxide but the patient developed renal failure and fluid retention. This case demonstrates that following Roux-en-Y gastric bypass in non-obese patients GLP-1 dependent hyperinsulinaemic hypoglycaemia can occur. This suggests that excessive GLP-1 and insulin secretion develop post surgically as a response to Roux-en-Y rather than causing obesity by excessive insulin production. Diazoxide is an effective treatment in this scenario.
Declaration of interest: There is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported.
Funding: No specific grant from any funding agency in the public, commercial or not-for-profit sector.