What is Insulinoma ?

In general an Insulinoma is a neuroendocrine tumor which is rare. The name itself tells you a bit about where it is and what it does. This article will give you the signs and symptoms, testing or work up, treatments, prognosis, causes, and possible differences between the before mentioned in humans or animals. Insulin is a hormone produced in the pancreas. Insulinoma is a tumor found in the islets of Langerhans cells located in the pancreas.

Physiology of the Insulinoma

  • Initiates in the cells which secrete insulin. These cells are called Beta cells.
  • In response to an increase in blood glucose beta cells function by releasing insulin.
  • Insulin is a hormone which decreases blood glucose levels.
  • At the moment the blood glucose is at its proper level the beta cells stop releasing insulin.
  • When there is an insulinoma the beta cells continue secreting insulin and the blood glucose continues to drop lower than the normal level.
  • This drop in blood glucose is the cause of most all the signs and symptoms of an insulinoma.

Facts about Insulinoma

  • The percentage of persons found with this type of tumor is very small.
  • Most insulinoma tumors in humans as well as animals are usually benign meaning non-cancerous.
  • Knowing if the tumor is cancerous or noncancerous will not change the symptoms but may change the treatment and prognosis as discussed below.

Signs and Symptoms of Insulinoma:

Neuroglycopenic symptoms due to hypoglycemia:

  1. Recurrent headache regardless of when the patient ate last.
  2. Anxiety – The body notices the low blood sugar causing may of the other symptoms noted. These symptoms cause the patient to have anxiety.
  3. Behavior changes – Low blood sugar causes the brain to react slowly, this initiates behavior changes.
  4. Confusion – Low blood sugar causes the brain to react slowly, causing the confusion.
  5. Lethargy – Muscles need a normal blood sugar to function correctly. Due to the decrease in blood sugar muscles are slow to react causing lethargy or general weakness.
  6. Diplopia(double vision) and Blurred vision – A decrease in blood sugar lower than normal ranges causes the nerve conduction needed for proper sight to function slowly.
  7. Sweating
  8. Anxiety
  9. Nausea
  10. Rarely weight gain will be noted.
  11. Hypoglycemia – sometimes causing seizures or coma as well as neurological damage.
  12. There is a very uncommon Catecholaminergic response to hypoglycemia cause cardiac symptoms such as:
  • Tremulousness
  • Palpitations
  • Tachycardia
  • Sweating
  • Hunger


Testing / Work up

The testing required will be according to all your symptoms and previous illness. All physicians may choose a different path. Here are listed some of the tests that may be administered to determine the diagnosis of insulinoma. The testing is not limited to this list nor will the physician always need to complete all testing noted below:

a. Symptomatic fasting hypoglycemia

This is basically a fasting process in which any and all symptoms are noted during the time period indicated by the prescribing physician.

b. Whipple’s triad

  1. When patient symptoms are most likely to be cause by hypoglycemia after fasting or much exercise.
  2. A low glucose plasma measured during patients known symptoms
  3. When glucose is raised to a normal rate there is an absence of symptoms.

c. Blood testing

  • Glucose – could be fasting or not fasting depending on symptoms and physician preference.
  • Insulin levels.
  • C-peptide – is a substance which is also made by the beta cells located in the pancreases. This substance is usually made at the same rate as insulin and may assist in reading insulin production in the patient.
  • Proinsulin – is a substance which causes the split between insulin and C-peptide.
  • Insulin suppression test (inpatient with blood draws every 4 hours)

d. The following are scans and other testing which can assist the doctor to see the size and shape of the pancreas in the patient.

  1. Ultrasound
  2. CT scan
  3. MRI
  4. Endoscopic ultrasound
  5. Angiography


  • Partial surgical removal – This is done when the whole pancreas is not affected.
  • Complete surgical removal – This is necessary when the entire pancreas is affected and must be removed. In this case there will be more follow up care and medication needed to provide the body all the hormones necessary to regulate blood glucose levels.
  • Whipple procedure – as stated above.
  • Distal pancreatectomy
  • Hepatic arterial occlusion
  • Embolization
  • Medications :
  1. Diazoxide
  2. Somatostatin
  3. Streptozotocin
  4. Chemotherapy (Doxorubicin + streptozotocin  and Fluorouracil + streptotozocin )


The prognosis for patients with this type of tumor is very good when it is benign, as most are. If the patient does not have multiple tumors there is a very small chance they will continue to suffer from hypoglycemia. Some patients with multiple tumors may continue to suffer from hypoglycemia after surgery. An extremely small percentage of patients may present with diabetes mellitus after surgery.


Genetic disposition to multiple endocrine neoplasia type I.

Possible complications:

  • Acute or sever hypoglycemic reactions
  • If the tumor is cancerous- metastasis or spreading of cancerous cells.

Should I contact a doctor? If you note any of the following symptoms of hypoglycemia you should contact your doctor.

  1. Diplopia (double vision)
  2. Blurred vision
  3. Palpitations
  4. Weakness
  5. Confusion
  6. Abnormal behavior
  7. Unconsciousness
  8. Amnesia
  9. Adrenergic symptoms such as:
  • Weakness
  • Sweating
  • Tachycardia
  • Palpitations
  • Hunger


Insulinoma in Dogs (Pets)

In pets such as dogs, ferrets, cats and other animals the symptoms may be noticed differently. This is because your animal can not communicate many of the normal symptoms. Usually before hypoglycemia is noted in pets and animals they collapse or have a loss of consciousness.

Other sever symptoms may be noted such as neurologic abnormalities, extreme weakens or seizures. Many times these symptoms may not be noticed right away by the owner for various reasons. At times it is because of lack of visualization of pets or animals at all times.

But other times it is because the symptoms come and go an may not be constant or at any regular pattern. Testing, prognosis, as well as treatment for pets or animals is the same as with humans.



Published by Dr. Rajesh MD under Diabetes Information.
Article was last reviewed on January 8th, 2022.

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