Abstract
A 63-year-old man was admitted to a hospital in April 2012 with a disturbance of consciousness and subsequently diagnosed as being in a hypoglycemic coma based on his low plasma glucose (PG) level. He consequently recovered after receiving an intravenous infusion of glucose and was admitted to our hospital for a further examination of the hypoglycemia. On admission, the patient's fasting PG level was low (43 mg/dl), whereas the immunoreactive insulin (IRI) level was slightly high; the IRI/PG ratio was not above 0.3. A 75 gOGTT showed impaired glucose tolerance, and the plasma proinsulin level was markedly high (70.7 pmol/l). In addition, abdominal CT disclosed a hypervascular tumor in the tail of the pancreas, and a selective arterial calcium injection test was therefore performed. Consequently, a marked rise in the IRI level was observed when calcium was infused into the splenic artery, suggesting that the tumor was an insulinoma, and distal pancreatectomy was subsequently performed. After the surgery, the fasting PG level remained elevated (89 mg/dl), while the plasma proinsulin level markedly decreased (6.3 pmol/l). These observations suggest that the patient's hypoglycemia was principally caused by hyperproinsulinemia due to insulin secretion from the insulinoma.
