Glucagon-secreting pancreatic neuroendocrine tumour; glucagon-secreting pancreatic islet cell tumour; pancreatic islet alpha cell tumour; glucagonoma syndrome; 4D syndrome
Glucagon is a hormone, which is normally released from alpha cells in the pancreas in response to low levels of blood sugar. After glucagon is released, it acts on the liver to turn glycogen into glucose, which is then released into the bloodstream, increasing blood glucose levels and returning blood sugar levels back to normal.
A glucagonoma belongs to a family of tumours called neuroendocrine tumours (NETs), which are tumours that occur in parts of the body that release hormones in response to stimulation by nerves. A glucagonoma is a tumour in the alpha cells of the pancreas that results in too much of the hormone glucagon being produced. Unfortunately, at the point of diagnosis, the majority (~80%) of glucagonomas have already spread and caused secondary (metastatic) tumours in other parts of the body, most commonly the liver. These are termed malignant glucagonomas.
In the majority of cases there is no known reason why a glucagonoma occurs. However, in a small number of cases, the glucagonoma is linked to an inherited condition called multiple endocrine neoplasia type 1 syndrome.
Glucagonomas do not usually present with clear or specific symptoms because the tumour is known to grow slowly. As the tumour grows, the amount of glucagon released by the tumour will continue to increase. As this happens a number of key symptoms may start to become noticeable:
It is also important to think about any previous hospital admissions associated with blood clots such as a pulmonary embolism or a deep vein thrombosis. This may point towards an increased risk of developing blood clots, which is also one of the signs of a glucagonoma.
Glucagonomas are extremely rare. In the UK, it has been estimated that each year one case of glucagonoma is diagnosed per million people.
The majority of glucagonomas are not inherited. However, a minority of cases are linked to a genetic disorder known as multiple endocrine neoplasia type 1.
The first test carried out in a suspected case of glucagonoma is a fasting blood sugar test. This is normally done in an outpatient setting. This test measures the amount of sugar in the blood. Before doing the test, the patient should not eat anything for eight hours (usually overnight). If a glucagonoma is present, then the result of the fasting blood sugar test will be much higher than normal.
A test called a fasting gut hormone profile is taken from patients suspected of having a glucagonoma to measure the levels of chemicals such as glucagon and chromogranin A. Normally levels of chromogranin A in the blood are low, but if a glucagonoma (or any other neuroendocrine tumour) is present, levels of chromogranin A in the blood will be increased. A patient with a glucagonoma may also produce other hormones such as pancreatic polypeptide, which may be detected as part of the fasting gut hormone screen. Imaging tests are then used to localise the glucagonoma. These might include:
Typically, glucagonomas are not difficult to find and an abdominal ultrasound and/or CT/MRI are often sufficient.
If it is suspected that the glucagonoma is due to the inherited condition multiple endocrine neoplasia type 1, blood samples can be taken to look for other abnormalities typically found in this condition. If the results show that the patient has multiple endocrine neoplasia type 1, the patient will be seen by a genetic specialist at an outpatient clinic to discuss what this means for them. See the article on multiple endocrine neoplasia type 1 for further information.
The first part of treating a glucagonoma is to manage the symptoms. This usually involves having to take anti-diabetic tablets or insulin injections to manage the high blood sugar levels. For the rash, this is often managed by taking supplements of amino acids and zinc whilst also applying skin cream over the rash.
The main treatment for removing the glucagonoma is surgery, which is usually done as an inpatient at a specialist hospital. Here the tumour is removed by a specialist pancreatic surgeon in conjunction with the endocrine (hormone specialist) team. In some situations the spleen may also have to be removed but this depends on the exact location of the glucagonoma. If they find that the tumour is large, then sometimes the surgeon will have to give the patient insulin to help control their blood sugar levels.