Hyperinsulinemic hypoglycemia associated with a neurofibrosarcoma

A patient with a posterior mediastinal malignant neurofibrosarcoma and recurrent episodes of severe hypoglycemia was demonstrated to have basal hyperinsulinemia on repeated study. Despite hypoglycemia, there was no glucagon response to aminogenic stimulation. No immunoreactive insulin was detected on extraction of the tumor and no secretory granules of beta type were seen on electron microscopic examination of tumor tissue. Following tumor removal, plasma glucose and insulin levels returned to normal. Alpha cell function improved. These findings suggest stimulation of pancreatic beta cell secretion and possible inhibition of alpha cell response by an extrapancreatic tumor.