Endocrine Abstracts

Introduction: Hypoglycaemia following bariatric surgery is a recognised complication, secondary to increased incretin secretion to nutrient intake due to altered gut anatomy. It is predominantly postprandial, and usually occurs >6 months postoperatively. We report a case of insulinoma unmasked during the early postoperative period after sleeve gastrectomy (SG).

Case presentation: A 49-year old female with severe obesity without diabetes underwent SG. Within 4-weeks, recurrent severe hypoglycaemic episodes were observed, with fasting glucose levels ranging from 1.1-2.9 mmol/l together with symptoms of sweating, palpitations, confusion & collapse. Hypoglycaemia appeared predominantly in fasting state and relieved with food intake. For a corresponding plasma glucose of 2.0 mmol/l, insulin was 26.9 mIU/l (4.4-26) & C-peptide 1119 pmol/l (298-2350) (inappropriately unsuppressed), indicating insulinoma biochemically. Sulphonylurea screen: negative, 3-hydroxy-butyrate: 0.1 mmol/l, IGF-1: 81 ng/l (53-215) and 9am cortisol: 322 nmol/l. IGF-2 not processed yet. Computed Tomography scan revealed an arterially hyper-enhancing 1.6 cm pancreatic body lesion avid on FDG-PET confirming an insulinoma. FDG-non avid incidental 6.5 cm possible right renal cell carcinoma was also noted.

Progress: Monthly lanreotide injection was initiated to prevent hypoglycaemias; currently awaiting surgery for removal of both tumours.

Discussion: Obesity induced severe insulin resistance appeared to have negated the insulin action at tissue receptors despite hyperinsulinaemia from insulinoma. The rapid improvement in insulin resistance due to calorie restriction and weight loss post-SG triggered hypoglycaemias, unmasking an underlying insulinoma during the early postoperative period. IGF2:IGF-1 ratio is typically >3 and insulin and C-peptide are suppressed in Non-Islet Cell Tumour Hypoglycaemia- hence renal carcinoma even if diagnosed in this case, is not the cause of hypoglycaemia.

Learning points: 1) Post-bariatric surgery fasting hypoglycaemias, especially within the first 6 months, should raise the suspicion for insulinoma. 2) Insulinoma differential should be considered if fasting hypoglycaemias occur after definitive treatments for other insulin resistant states (for example Cushing’s syndrome).