A 45 year-old man was referred to the Endocrinology clinic with 3-months history suggestive of post-prandial hypoglycaemia (PPH), including one episode resulting in syncope and facial injury. Sugary drinks precipitated these episodes. He was otherwise healthy and has not had gastric or fundoplication surgery. There is a family history of paternal uncle with pancreatic cancer, and grandmother with hyperparathyroidism.
75gOGTT confirmed the diagnosis of proinsulinoma, with symptomatic hypoglycaemia (2.3mmol/l) occurring at 120minutes, associated with failure of suppression of insulin and proinsulin (544.2mIU/l and >100pmol/l respectively). Intriguingly, 72-hour fast did not precipitate hypoglycaemia (BGL 5mmol/l at start to 3.4mmol/l at 72hours with low beta-hydroxybutyrate 2.2mmol/l).
Imaging confirmed an intensely DOTATATE-avid 27x26x26mm head of pancreas lesion. Selective arterial calcium stimulation (SACS), however, returned with discordant localisation to the pancreatic tail and also indicated liver metastasis. Biopsy performed via endoscopic ultrasound (EUS) of the pancreatic head lesion further confirmed a well-differentiated insulinoma. As liver lesions were not identified on DOTATATE-PET, MRCP and EUS, a pancreatico-duodenectomy with intra-operative ultrasound has been planned for June’2018. Diazoxide was commenced in the interim with good effect.
To our knowledge, there have been less than ten cases of insulinoma reported with both isolated PPH and negative 72-hour fast. Mechanisms hypothesised include (1) predominance of Glut-2 expression1, (2) over-expression of GLP1 receptors2, and (3) prolonged half-life of insulin after a significant insulin surge3. Despite only 6% of insulinomas presenting with exclusively post-prandial symptoms4, insulinoma should be considered in the differentials for PPH after common causes are excluded.
Majority of insulinomas are benign. This case will require long-term observation due to several factors suggestive of malignancy including early presentation, markedly elevated proinsulin (>40% total insulin)5, and positive SACS for liver metastasis with negative imaging.
Further operation details, immunohistochemistry, and post-operative outcome will be discussed during the presentation.