Hypoglycemia
History. You examine an 8-year-old male boxer dog whose owner complains that the dog experiences seizures, weakness, and confusion around the time he is fed.
Clinical Examination.
The findings of the dog’s physical examination, including his neurological examination, were within normal limits. His fasting serum glucose level, however, was 29 mg/dL (normal, 70-110 mg∕dL), and the ratio between serum insulin and serum glucose levels was significantly elevated.Comment. Neurons depend primarily on oxygen and glucose as metabolites for ATP energy production, and neurons cannot store appreciable quantities of glucose. ATP is needed for maintenance of the normal electrical membrane potential. When deprived of glucose and subsequently ATP, the brain does not function properly; associated clinical signs include seizures, weakness, and confusion. In this animal, these signs were more common at the time of feeding because as the dog anticipated eating or actually did begin to eat, insulin was released, causing hypoglycemia.
In this case the ratio of insulin to glucose is elevated, probably because of an insulin-secreting tumor of the pancreas. Because insulin facilitates glucose transport through cell membranes, too much insulin results in the transfer of too much serum glucose to the cytoplasm of other cells of the body, thus depriving the brain’s neurons of this essential metabolite.
Treatment. Insulinomas can usually be found and removed from the pancreas surgically. After surgical removal of the tumor, additional medical treatment is warranted to maintain normo- glycemia. Medications include glucocorticoids, to stimulate gluconeogenesis; diazoxide, to inhibit insulin secretion;
Streptozocin, which is toxic to the beta cells; and somatostatin, which increases gluconeogenesis. With this tumor type, there is a high rate of metastasis, which means that other tumor sites may remain, in the liver and elsewhere, to overproduce insulin.