Insulinoma

Q: In insulinoma, hypoglycemia is primarily due to? (select one)

A) increased glucose utilization

B) reduced hepatic glucose output

Answer: B

There is a common misconception that as insulinoma causes high insulin output, symptoms occur due to increased glucose utilization. In reality, this is due to reduced hepatic glucose output. The fasting state tends to pronounce symptoms more intense, though a large number of patients report postprandial hypoglycemia. Symptoms are usually subtle and may go undiagnosed. One out of five patients get mislabeled as having a neurologic or psychiatric disorder. Some may even develop seizures.

Once a clinician suspects insulinoma, the meticulous application of the 'art' of differential diagnosis helps establish the diagnosis coupled with invasive and non-invasive testing. Treatment is usually surgical.

One exciting test worth mentioning regarding the question above is selective arterial calcium stimulation (SACT). The test is based on the belief that calcium stimulates insulin release from hyperfunctional beta cells but not the normal beta cells. Calcium stimulates insulin release in the same arterial territory as the abnormal beta cells, which helps localize the operative boundaries. The test is carried out by selective injection of calcium gluconate into the gastroduodenal, splenic, and superior mesenteric arteries with subsequent sampling of the hepatic venous effluent for insulin. This test also helps in differentiating between insulinoma and nesidioblastosis.

#endocrinology

References:

1. Rizza RA, Haymond MW, Verdonk CA, et al. Pathogenesis of hypoglycemia in insulinoma patients: suppression of hepatic glucose production by insulin. Diabetes 1981; 30:377.

2. Dizon AM, Kowalyk S, Hoogwerf BJ. Neuroglycopenic and other symptoms in patients with insulinomas. Am J Med 1999; 106:307.

3. Doppman JL, Miller DL, Chang R, et al. Insulinomas: localization with selective intraarterial injection of calcium. Radiology 1991; 178:237.

4. Okabayashi T, Shima Y, Sumiyoshi T, Kozuki A, Ito S, Ogawa Y, Kobayashi M, Hanazaki K. Diagnosis and management of insulinoma. World J Gastroenterol. 2013 Feb 14;19(6):829-37. doi: 10.3748/wjg.v19.i6.829. PMID: 23430217; PMCID: PMC3574879.