Conditions related to the regulation of blood sugar levels are unfortunately all too common in the United States. Hypoglycemia, the medical term used to describe the state of having low blood sugar, is one such condition that afflicts many people. Even though hypoglycemia has a well-documented link to type 1 and type 2 diabetes, that isn’t the only associated condition. One relatively rare condition that can potentially cause hypoglycemia is a kind of tumor called an insulinoma. 

What is an Insulinoma?

Rather than referring to an overall condition, an insulinoma is the term for a type of neuroendocrine tumor that develops inside the pancreas. The pancreas, which is an organ that is part of both the digestive system and endocrine system, is primarily responsible for secreting pancreatic juice into the digestive tract and regulating blood sugar through the secretion of the hormone insulin. Changes and fluctuations in the regulation of blood sugar are behind problems like hypoglycemia and diabetes mellitus (among others), but these changes can also lead to the development of an insulinoma. 

An insulinoma is a rare type of pancreatic neuroendocrine tumor (meaning that it interacts with the nervous and endocrine systems) that forms exclusively in the pancreas. The vast majority of these cell tumors are noncancerous and benign (also known as an adenoma), though in some very rare cases they have been known to metastasize and spread to other areas of the body. Generally, though, malignant insulinoma is a rare condition and instead is usually restricted to the pancreas. 

Doctors and scientists still don’t know what causes an insulinoma, but what is known is that they derive from beta cells. Beta cells are the pancreatic cells (formed from proinsulin and c-peptide in the pancreatic islet cells) that actually secrete insulin into the bloodstream when an increase in blood sugar is detected. Normally when blood sugar is high, the secretion of insulin is triggered by the body in an effort to reduce blood glucose to normal levels. A classic example of a high blood sugar event would be eating a lot of sugary foods in one sitting, but for diabetics and other people with pancreatic conditions, blood sugar fluctuations can happen even without eating something specific. 

Under normal circumstances, the pancreas stops secreting insulin once levels have returned to normal. When someone has an insulinoma, however, low or high insulin levels are no longer properly regulated by the pancreas. This means that the insulinoma tumors continue to secrete insulin beyond what is necessary, and the net effect is abnormally low blood sugar levels. As noted earlier, hypoglycemia is the term used to define the state of low blood sugar, and it is a common condition associated with the presence of insulinomas.  

Symptoms of Insulinoma

Conditions that affect the production of insulin and the regulation of blood sugar are fairly common in the United States even if these sorts of tumors of the pancreas are rare. In most cases, though, the symptoms of an insulinoma are notable for being very similar to typical hypoglycemic symptoms: weakness, fatigue, confusion, rapid heartbeat or heart palpitations, and excessive sweating. Another potential symptom that can occur when blood sugar levels are extremely low is passing out. In some severe cases, passing out can even lead to a coma. 

The general impact of low blood sugar is responsible for these symptoms because of how insulin functions. The reason the pancreas secretes insulin into the bloodstream is that the insulin can carry glucose—one of the body’s main sources of energy—throughout the body so that it can be used by the body’s cells. Cells that don’t have sufficient energy begin to “malfunction” or not function properly any longer. When the cells that make up various organs aren’t operating efficiently, the organs themselves also stop functioning properly. This can create a wide variety of symptoms and side effects, depending on the systems that are impacted.  

Risk Factors

Since the underlying cause of insulinomas is still unclear, the risk factors understood by doctors are also somewhat unclear. Generally speaking, though, women seem to be more likely to develop an insulinoma than men, and it also seems to be more common in people between the ages of 40 and 60. Other than that, there are a few rare genetic diseases passed on through family members that are believed to increase the chances of developing one of these tumors: 

  • Von Hippel-Lindau syndrome: a rare inherited disease that is characterized by a series of cysts and tumors that can develop throughout the body 
  • multiple endocrine neoplasia type 1 (MEN-1): one type of a group of disorders that causes lesions to form on part of the pancreas as well as some glands around the body
  • neurofibromatosis: a genetically inherited syndrome that negatively affects a type of protein synthesized by our cells that can cause tumors to form along the nervous system 
  • tuberous sclerosis complex: also a genetically inherited disease that can cause the formation of noncancerous tumors in vital organs all over the body

Diagnosis of Insulinoma and Treatment

Because of how similar the symptoms of hypoglycemia are to an insulinoma, diagnosing the condition can be difficult for doctors. In some cases it can take years of a patient experiencing symptoms and gradually ruling out other causes before an accurate insulinoma diagnosis is made. These diagnoses are especially difficult for people with diabetes or other conditions related to the pancreas or kidneys. 

One of the standard ways a doctor can test for an insulinoma is by instructing the patient to fast for several days while observing the results. During the typical 2-3 day fast, the doctor will do regular blood tests to determine glucose levels over time. Since blood sugar can fluctuate a lot depending on what you’ve eaten, observing glucose levels during a fast will allow the doctor to determine a base level. A person with fasting hypoglycemia would have very low blood sugar that may very well indicate the presence of an insulinoma.

If an insulinoma seems like a potential candidate for the cause of low blood sugar, the doctor might also order an endoscopic ultrasound (EUS), magnetic resonance imaging (MRI), or CT scan to take a closer look at the transabdominal area. Sometimes the actual tumor is too small to be seen even by advanced imaging tests, however. In these situations, blood samples directly from the pancreas can help definitively determine the presence of an insulinoma. 

There is no medicinal cure for an insulinoma, but the treatment options are nevertheless very promising. For some patients, the symptoms are mild enough that they can be managed simply by making dietary adjustments and medication like diazoxide. If those adjustments aren’t sufficient, laparoscopic surgery (sometimes known as the Whipple procedure) can be used to remove the tumor. For most people, the removal of an insulinoma through a pancreatectomy is essentially a cure that will resolve the symptoms and allow the body to return to normal insulin regulation. If surgery isn’t an option for any reason (some people are just not good candidates for surgery), it is possible to manage the condition with lifestyle changes like eating smaller meals. 

Gastroenterologist Appointment  

Even though pancreatic endocrine tumors are fairly rare, it is a good condition to understand for anyone who has an insulin production problem or is feeling symptoms that tend to be associated with severe hypoglycemia. Whether or not you actually have one, finding the root of a problem related to blood sugar levels is important for long term health as well as day-to-day life. At Cary Gastroenterology Associates, improving your health and quality of life is central to everything we do. If you’d like to speak with us about your digestive health, please request an appointment today!