SUN-339 Insulinoma Presenting With Postprandial Hypoglycaemia

Abstract P.M. Francis-Emmanuel: None. R.K. Thompson: None. K.G. Gabriel: None. P.O. Roberts: None. Background: Insulinomas have long been recognised as a cause of fasting and exercise-induced hypoglycaemia. Diagnosis is often delayed when insulinomas are associated with postprandial hypoglycaemia. Clinical case: A 56-year-old woman presented with a 10-year history of weakness, sweating, headaches, and palpitations occurring 2 to 3 hours after certain meals. These symptoms resolved upon eating. She identified specific foods, including dried cranberries, ripe bananas and naseberries, which triggered her symptoms. There was no flushing, diarrhoea, epigastric pain, or rash. She denied sulfonylurea use, had experienced gradual weight gain over several years, and had no immediate family history of diabetes. There was a remote history of peptic ulcer disease, but this had been managed conservatively. She had a body mass index of 29.1 kg/m2 with no cushingoid features. Over the 10-year period, several investigations were done by her primary care physician. In summary, HbA1c was 5.0% (<6.5%), TSH 1.1 (0.3 - 5) mIU/L, plasma free metanephrines 58 (<57) pg/mL, plasma free normetanephrines 49 (<148) pg/mL and urinary 5-HIAA 9 (<46) mg/day. An abdominal CT scan revealed a 1.7 x 1.4 cm round/well-demarcated, arterially enhancing mass within the pancreas at the junction of the body and tail. Given her presenting symptoms which persisted after 10 years, post prandial hyperglycaemia was suspected and a meal tolerance test (consisting of the symptom-inducing foods) was performed. Due to a lab error, C-peptide levels were not simultaneously measured. Urinary/blood sulfonylurea testing was not locally available. Blood glucose and insulin levels (recorded in that order) at times 0 (fasted), 30, 60, 90, 120, 150 and 180 minutes were as follows: T0 = 3.6 (4 - 7) mmol/L and 7.1 (<19.6) uIU/mL; T30 = 2.7 mmol/L and 945 uIU/mL; T60 = 1.8 mmol/L and 423.3 uIU/mL; T90 = 1.6 mmol/L and 166 uIU/mL; T 120 = 2.7 mmol/L and 38.9 uIU/mL; T150 = 1.8 mmol/L and 25.6 uIU/mL; T180 = 1.8 mmol/L and 22.7 uIU/mL Serum chromogranin A 229 (<311) ng/mL. A low glycaemic index diet was prescribed, in view of documented post-prandial hypoglycaemia, and she experienced some improvement in her symptoms. Image-guided biopsy was later done, and histology revealed a well-differentiated neuro-endocrine tumour which was positive for chromogranin and insulin but negative for glucagon on immunohistochemistry. Mitotic count was <1mf/hpf. She had successful enucleation with resolution of symptoms and a 10% weight loss over 17 months. Insulinomas are readily suspected when non-diabetic patients present with fasting or exercise-induced hypoglycaemia. Postprandial hypoglycaemia may also be associated with insulinomas; however, the diagnosis is often delayed. A high index of suspicion is needed to avoid these diagnostic delays as longstanding untreated insulinomas often lead to hypoglycaemia unawareness which may increase morbidity and mortality. Sunday, June 2, 2024