All About Insulinomas: Symptoms, Diagnosis, and Treatment

Medically Reviewed By Saurabh Sethi, M.D., MPH
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An insulinoma is a rare tumor of the pancreas that is almost always benign. Insulinomas are named for the insulin they release. They can cause symptoms due to low blood sugar such as sweating, headache, and anxiety. The main treatment for insulinomas is the surgical removal of the tumor.

This article will discuss insulinomas, including tests to diagnose insulinomas, treatment options, and more.

What is an insulinoma?

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An insulinoma is a small, typically noncancerous tumor that develops on your pancreas. Medical professionals classify it as a pancreatic neuroendocrine tumor (pNET).

More than 94% of insulinomas are benign, according to a 2022 review. They appear rarely as several small tumors, most often in people with multiple endocrine neoplasia type 1 (MEN1), a genetic condition.

How your body uses insulin

To understand insulinomas, it is helpful to know how your body uses insulin. 

Your pancreas helps your body use the glucose in your bloodstream as energy by creating insulin and releasing it after a meal. Insulin helps the cells in your body use the glucose (blood sugar) more efficiently, lowering your blood sugar.

Like your pancreas, insulinomas also release insulin into your body. However, unlike your pancreas, insulinomas do not regulate their insulin production according to blood sugar levels. They continue to release insulin, which can lead to too much insulin in your bloodstream, a condition known as hyperinsulinemia. This can lead to hypoglycemia — low blood sugar.

An insulinoma is what clinicians call a functional tumor: They are a tumor that makes hormones.

Learn about hyperinsulinemia here.

What causes an insulinoma?

Many insulinomas do not have a specific cause. Sometimes they are due to a genetic tumor syndrome known as MEN1.

People with this syndrome have a higher chance of developing insulinomas and other tumors. MEN1 is due to an inherited mutation in the MEN1 gene, a gene known as a tumor suppressor. The MEN1 mutation disrupts its function as a tumor suppressor, and this allows tumors to develop.

A 2019 article in Frontiers in Endocrinology states that insulinomas are the second most common type of functional tumor in the pancreas. About 4% of insulinomas occur in people with MEN1.

MEN1 insulinomas typically occur in individuals younger than 40 years. Other insulinomas tend to develop later.

Experts estimate that fewer than 5,000 people in the United States have insulinomas, according to the Genetic and Rare Diseases Information Center.

Genetic syndromes that increase the chance of developing an insulinoma include:

  • Von Hippel-Lindau syndrome
  • neurofibromatosis type 1
  • tuberous sclerosis 

What are the symptoms of an insulinoma?

The extra insulin in your body from an insulinoma can cause hyperinsulinemia, or too much insulin. Because insulin acts to clear glucose from the blood, hyperinsulinemia can cause symptoms of hypoglycemia. Together, the symptoms can range from mild to severe and include:

People with an insulinoma sometimes experience more severe symptoms, including losing consciousness, after not eating for several hours (fasting) or skipping a meal. This is fasting hypoglycemia.

Contact your doctor if you experience hypoglycemic symptoms.

Hypoglycemia can lead to neurological problems. Seek immediate emergency medical help by calling 911 with severe symptoms, including:

How do doctors diagnose insulinomas?

If your doctor thinks you could have an insulinoma, they will evaluate you for a combination of the following signs and symptoms known as Whipple’s triad:

  • symptoms of hypoglycemia
  • low blood glucose
  • an improvement of symptoms with glucose treatment

They may ask you to stay in the hospital for a few days to run some tests such as:

  • a 72-hour fast while monitoring the blood level of:
    • blood sugar
    • insulin
    • proinsulin
    • beta-hydroxybutyrate, a ketone body
    • sulfonylurea
  • a C-peptide, a marker for insulin secretion, which could be elevated if you have an insulinoma

The other part of diagnosis is locating the tumor. The care team will likely use some kind of imaging test, such as a CT, MRI, or PET scan. Sometimes insulinomas are too small or the scan does not detect them, or both. In this case, your doctor might request:

  • an endoscopic ultrasound to look inside your body at your pancreas
  • an octreotide scan, which checks for neuroendocrine tumors
  • a pancreatic arteriogram, which evaluates the arteries of the pancreas
  • a pancreatic venous sampling for insulin, which helps to locate a pancreatic tumor

Arriving at a diagnosis of insulinoma can take some time because they are not a common cause of hypoglycemia. Also, the symptoms may develop slowly or are attributed to other causes. Your doctor may start with tests for more likely causes and narrow them down to insulinoma.

How do doctors treat insulinomas?

Insulinoma treatment usually involves procedures to remove the tumor and medications to manage symptoms until the tumor is gone. The specific treatment plan depends on whether the tumor is benign or malignant (cancerous) and other factors.

Surgical removal is often the first-line treatment to remove the tumor and potentially part of the pancreas. This may occur with open abdominal surgery or laparoscopic surgery, a minimally invasive procedure in which the surgeon inserts surgical instruments through small “keyhole” incisions.

Some medications also help lower insulin levels, including diazoxide (Proglycem) and octreotide (Sandostatin).

Treatment options for malignant pancreatic neuroendocrine tumors may include liver-directed therapy, chemotherapy, and targeted cancer therapy, according to the 2020 guidelines from the North American Neuroendocrine Tumor Society (NANET). Learn how targeted therapy works.

If you have an insulinoma, talk with your doctor about all of your treatment options and the benefits and risks of each.

How can you balance blood sugar with an insulinoma?

A nutritious eating plan can help you manage low blood sugar. Carbohydrates turn into glucose in your body, but it is important to choose healthy carbohydrates, such as whole grains and brown rice.

Eating evenly spaced snacks and meals helps you balance blood sugar levels. Your body digests protein slower than carbohydrates and also can be a good choice to maintain blood sugar.   

Read What to Eat When You Have Low Blood Sugar.

What is the outlook?

Surgery can cure a benign insulinoma and hypoglycemia. Even without surgery, about 60% of people who take Proglycem to manage hyperinsulinemia report no symptoms of an insulinoma.

The outlook for malignant insulinomas varies by the size of the tumor, where it is growing, and treatment. Targeted therapy has increased survival for people with incurable neuroendocrine tumors, according to a review of trials. Talk with your doctor about what to expect based on your individual circumstances.

Other frequently asked questions

Saurabh Sethi, M.D., MPH, reviewed the following questions.

Is insulinoma cancer?

Nearly all insulinoma tumors are not cancer. They are usually benign and very rare.

Is C-peptide level high in insulinoma?

During fasting, C-peptide levels may be elevated in people with insulinoma.

Summary

An insulinoma is a tumor on your pancreas that is secreting insulin. Most insulinomas are not cancer. However, insulinomas cause high insulin levels and hypoglycemia, which can cause mild to severe symptoms. Also, without treatment, insulinomas can be life threatening.

Surgery to remove an insulinoma can cure the syndrome. Nonsurgical treatment options include medications. This includes targeted cancer therapy for cancerous insulinomas that are incurable.

Early treatment is key to avoiding potentially dangerous symptoms of insulinomas.

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Medical Reviewer: Saurabh Sethi, M.D., MPH
Last Review Date: 2022 Aug 22
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THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.
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