An insulinoma is a rare type of pancreatic tumor that secretes insulin, a hormone that lowers the levels of sugar (glucose) in the blood.
Insulinomas are a type of pancreatic endocrine tumor. Only 10% of insulinomas are cancerous. The average age at diagnosis is 50.
Symptoms result from low levels of sugar (glucose) in the blood, which occur when the person does not eat for several hours (most often in the morning after an all-night fast). The symptoms include faintness, weakness, trembling, awareness of the heartbeat (palpitations), sweating, nervousness, and profound hunger. Other symptoms include headache, confusion, vision abnormalities, unsteadiness, and marked changes in personality. The low levels of sugar in the blood may even lead to a loss of consciousness, seizures, and coma.
Diagnosing an insulinoma can be difficult. Doctors try to perform blood tests while the person has symptoms. Blood tests include measurements of blood glucose levels and insulin levels. Very low levels of glucose and high levels of insulin in the blood indicate the presence of an insulinoma. Because many people have symptoms only occasionally, doctors may admit them to the hospital. In the hospital, the person fasts for at least 48 hours, sometimes up to 72 hours, and is closely monitored. During that time, the symptoms usually appear, and blood tests are performed to measure the levels of glucose and insulin.
If the blood tests suggest the person has an insulinoma, the location must then be pinpointed. Imaging tests, such as endoscopic ultrasonography (which shows the lining of the digestive tract more clearly because the ultrasound probe is placed on the tip of the endoscope) or positron emission tomography (PET) scans, can be used to locate the tumor, but sometimes exploratory surgery is needed.
The primary treatment for an insulinoma is surgical removal, which has a cure rate of about 90%.
When the insulinoma cannot be completely removed and symptoms continue, drugs such as diazoxide or sometimes octreotide can help keep blood glucose from falling too low. Chemotherapy drugs may help control the tumor.
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