|An insulinoma is a
neuroendocrine tumor deriving mainly from pancreatic islet
cells that produce excessive amounts of insulin. About 90%
of insulinomas are benign. In healthy individuals, insulin
and C-peptide are secreted in equimolar quantities because
they derive from the same inactive precursor, proinsulin.
Normally, less than 20% of proinsulin is released directly
into the circulation.
Some insulinomas secrete additional
hormones, such as gastrin, 5-hydroxyindolic acid,
adrenocorticotropic hormone (ACTH), glucagon, human
chorionic gonadotropin, and somatostatin. The tumor may
secrete insulin in short bursts, causing wide fluctuations
in blood levels
Insulinomas are the most common pancreatic
endocrine tumor. The incidence is 4 cases per
million people per year. These make up 55% of
neuroendocrine tumors, as stated above in Background
The male-to-female ratio is 2:3.
- The median age at diagnosis is about 47
years, except in insulinoma patients with MEN 1,
in whom the median age is the mid 20s.
- In one series, patients with benign disease
were younger (mean age of 38 y) than those with
metastases (mean age of 52 y).
- Symptoms caused by effects of local tumor mass are
- About 85% of patients present with symptoms of
hypoglycemia with diplopia, blurred vision,
palpitations, or weakness.
- Other symptoms include confusion, abnormal behavior,
unconsciousness, or amnesia.
- About 12% of patients have grand mal seizures.
- Adrenergic symptoms (hypoglycemia causes adrenalin
release) include weakness, sweating, tachycardia,
palpitations, and hunger.
- Symptoms may be present from 1 week to as long as
several decades prior to the diagnosis (1 mo to 30 y,
median 24 mo, as found in a large series of 59
- Hypoglycemia usually occurs several hours after a
- In severe cases, symptoms may develop in the
postprandial period. Symptoms can be aggravated by
exercise, alcohol, hypocaloric diet, and treatment with
- Weight gain occurs in 20-40% of patients.
Insulinomas are characterized clinically by the Whipple
triad (which occurred in 75% of 67 insulinoma patients as
- Episodic hypoglycemia
- Central nervous system (CNS) dysfunction temporally
related to hypoglycemia (confusion, anxiety, stupor,
- Dramatic reversal of CNS abnormalities by glucose
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