Although insulinoma commonly presents as fasting hypoglycaemia it can rarely present as post prandial hypoglycaemia and even less rarely in association with Type 2 Diabetes Mellitus (T2DM). We describe a case of insulinoma presenting as post-prandial hypoglycaemia and T2DM.
A 60 year old man presented with a 6 year history of episodes of double vision and loss of concentration occurring post-prandially. His symptoms were associated with capillary blood glucose of less than 3 mmol/l and relieved with sugary drinks. A prolonged 5 h oral glucose tolerance test (OGTT) using capillary blood glucose showed 2 h glucose of 11.3 mmol/l, but no drop in blood glucose during the test. A diagnosis of T2DM was made subsequently using a standard OGTT (2 h glucose 11.3 mmol/l) to which patients post prandial hypoglycaemia was attributed. He was given dietetic advice for post-prandial hypoglycaemia and was followed up routinely.
After 2 years, hypoglycaemic symptoms worsened by exercise and delayed meals. A number of supervised fasting glucose measurements failed to demonstrate biochemical hypoglycaemia. His insulin, c-peptide and pro-insulin levels were mildly elevated but plasma glucose levels were normal. A CT scan showed 20 mm hypervascular lesion in the distal pancreas which was confirmed as insulinoma with pancreatic arterial calcium stimulation studies. Laparoscopic resection confirmed benign insulinoma and hypoglycaemia resolved. A repeat OGTT after 12 months showed T2DM and at 18 months impaired glucose tolerance.
Persistence of hypoglycaemic symptoms should always be taken seriously. Our case illustrates the importance of considering insulinoma as a cause of post-prandial hypoglycaemia. A high index of suspicion in patients with post-prandial hypoglycaemia, who do not respond to conventional treatment or whose pattern of symptoms change will lead to further investigations.