A 56-year-old man was admitted for evaluation of progressive postprandial hypoglycemia over a ten-year period. The high concentration of fastirlg plasma ilnmuoreactive insulirl (80μU/ml) with 34mg/dl of plasma glucose (PG), even though without hypoglycemic symptoms, suggested the presence of insulinoma. Excessive insulin secretion was also observed after meals (2h after breakfast: insulin 307μU/ml, PG 118mg/dl). Oral and intravenous glucose tolerance tests and the glucagon test resulted in excessive insulin secretion with peaks of 1040μU/ml, >9999μU/ml and 2768μU/ml, respectively. PG concentrations duriag intravenous glucose tolerance and glucagon tests decreased to less than 30mg/dl. A fasting exercise test performed suppressed insulin secretion from 31μU/ml to 6μU/ml at 60min and fasting raised PG from 48mg/dl to 82mg/dl. A 2cm tumor in the head of the pancreas was removed and identified histologically as a benign insulin-secreting islet cell tumor.
In summary, we report a rare case of insulinoma characterized by excessive insulin secretion in response to glucose, and therefore, postprandial hypoglycemia.