insulinoma
Meaning of insulinoma: A small pancreatic tumor that keeps releasing insulin when blood sugar is already low, producing confusing spells of odd behavior.
Definition of insulinoma
An insulinoma is a tumor arising from the insulin-producing beta cells of the pancreas. It releases insulin without regard to the blood sugar level, so sugar keeps falling instead of being defended. Most are small, single and not cancerous. The resulting attacks of low blood sugar bring sweating, tremor, hunger, confusion and sometimes loss of consciousness, often mistaken at first for a neurological or psychiatric problem.
Why does it cause such confusing symptoms?
Symptoms come in two waves. As blood sugar falls, the body releases adrenaline, producing sweating, shaking, a racing heart and hunger. If sugar keeps falling, the brain itself runs short of fuel, and the result is confusion, strange behavior, slurred speech, seizures or collapse. Because the brain is affected, the episode may be witnessed rather than described, and epilepsy, stroke, intoxication and psychiatric illness are all considered before the pancreas is. Attacks that come on with fasting or exertion and clear rapidly after eating are the pattern that points elsewhere.
How is it recognized?
| Feature | What is looked for |
|---|---|
| Symptoms | Occur during a low sugar reading and clear when it is corrected |
| Insulin level | Inappropriately high while sugar is low |
| C-peptide | Also high, showing the insulin came from the body |
| Supervised fast | Reproduces the episode under observation |
C-peptide is the key discriminator. The pancreas releases it alongside insulin it makes itself, while injected insulin contains none, so a low reading with high insulin points to insulin given rather than produced.
How does it differ from other pancreatic tumors?
It belongs to the neuroendocrine group, which arises from hormone-producing cells scattered through the gland, and not to the far commoner pancreatic cancer that arises from duct cells. Most insulinomas are a benign tumor, small enough that finding one on a scan can be difficult, and removing it resolves the episodes. A minority are malignant, and a minority occur as part of an inherited syndrome affecting several endocrine glands, which is why more than one tumor or a family history changes the assessment.
Also known as
Used in a sentence
Investigation for recurrent hypoglycemia identified a small insulinoma in the pancreatic tail.
Good to know
Insulin produced by the body is released with C-peptide while injected insulin is not, so measuring both separates an insulinoma from insulin that has been administered.
Word origin
Where “insulinoma” comes from
Combines insulin, from the Latin insula meaning island, with the Greek suffix -oma, a swelling or tumor.