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What is carcinoid syndrome?
Carcinoid syndrome is a rare condition with a set of symptoms that are caused by an underlying carcinoid tumor. Carcinoid tumors are cancerous growths of neuroendocrine tissue that can secrete various substances - as many as 40 different types - into the bloodstream. The main chemicals secreted by carcinoid tumors include serotonin, histamine, tachykinins, kallikreins and prostaglandins.
Carcinoid syndrome occurs in about 10% of people with carcinoid tumors, typically in people with more advanced tumors.  Carcinoid tumors are very rare and generally slow to grow and develop, but most commonly develop in the intestine or lungs. In particular, the majority of carcinoid tumors originate in the jejunum, ileum and caecum.
Carcinoid syndrome is associated with the development of carcinoid tumors, which cause high levels of certain chemicals to be released into the bloodstream. The cause of carcinoid tumors is not fully understood, but they may run in families.
For carcinoid syndrome, the risk factors may include:
Typical carcinoid syndrome
This is the most common form of carcinoid syndrome. It is most often caused by carcinoid tumors that have spread (metastasized) to the liver. It is characterized by brief periods of hot flushing, diarrhea, coughing, wheezing and shortness of breath. The flushing tends to be light pink to deep red and is commonly triggered by stress, alcohol, exercise and certain foods. Typical carcinoid syndrome is frequently linked to excess serotonin levels.
Atypical carcinoid syndrome
This is a rare form that is characterized by extended periods of hot flushing, headache and shortness of breath. The flushing tends to be deep purple, may last for hours, and can be followed by increased blood flow to the limbs and trunk. The flushing is not brought on by food.
Signs and symptoms
In the early stages of the carcinoid tumor's development, there are usually no visible symptoms, because the liver clears away the substances that the tumor produces and secretes. However, once the tumor has spread to the liver, the liver is no longer able to remove the chemical products and they circulate freely throughout the body. As the chemicals circulate, they may start to cause the onset of various symptoms.
There may not be any symptoms associated with carcinoid syndrome. When symptoms do occur, they may vary depending on the site of the carcinoid tumor and the substances being secreted into the bloodstream.
Most common symptoms
Episodic flushing is the main sign of carcinoid syndrome. It usually appears suddenly and lasts for 20-30 seconds. It primarily appears on the face, neck and upper cheeks. More severe flushes are associated with a fall in blood pressure and rise in pulse rate. The flushing is associated with the release of histamine.
Flushing symptoms may be worsened with physical exertion, stress or drinking alcohol, or be associated with dietary triggers, such as eating aged cheese, salted or pickled meats or other foods high in tyramine.
Diarrhea is a very common symptom of carcinoid syndrome. Episodes of diarrhea may occur several times a day, cause dehydration, and interfere with daily life.
Bronchospasms and wheezing
Breathing problems are a common symptom of carcinoid syndrome that may be mistaken for asthma. They are caused by the constriction of blood vessels, which makes it difficult to breathe.
Some less common symptoms of carcinoid syndrome may include:
Methods for diagnosis
There is often a delay in the diagnosis of carcinoid syndrome because the initial symptoms can be vague and occur sporadically. However, early diagnosis is very important in improving the outcome for people with the condition.
Blood and urine tests
In healthy people, only around 1% of dietary tryptophan is converted to serotonin, whereas in people with carcinoid syndrome, a much greater proportion - up to 70% - of dietary tryptophan is converted to serotonin. The serotonin is then broken down into a compound called 5-hydroxyindoleacetic acid (5-HIAAA).
During diagnostic screening for carcinoid syndrome, the altered metabolism of tryptophan typically results in abnormally high levels of 5-HIAAA in the urine and/or blood. When a urine test indicates normal 5-HIAAA levels in someone suspected of having carcinoid syndrome, a blood test may instead be used to confirm the diagnosis.
An octreoscan can be used to see hormone-producing tumors of the neuroendocrine system. In an octreoscan, a small amount of radioactive material and a hormone-like substance that is attracted to the carcinoid tumor is injected into a vein. After a few hours, a camera is used to detect where the material has been taken up.
An endoscopy may be performed to closely examine the digestive tract. This involves using an endoscope, which is an instrument with a small camera that allows the internal lining of the digestive tract to be viewed.
A biopsy may be used to clearly identify the type of tissue present in a suspected tumor and involves taking a small tissue sample from the tumor for laboratory testing.
Types of treatment
Treatment will vary depending on the size of the tumor, its location and where it has spread.
Surgery is typically the first choice of treatment for tumors, especially when they are found early and confined to a small area. Many small tumors can be completely removed with surgery, while larger tumors may require more extensive surgery. When the tumor is too large, or has spread too far, surgical removal may not be a viable option.
If the tumor cannot be removed through surgery, medication can help relieve symptoms.
The most commonly used drug is octreotide, which can help relieve symptoms in the majority of people and may also help to slow the tumor's growth.
Other medication may include:
- Antihistamines, to treat the facial flushing;
- Bronchodilators, to treat the wheezing and help ease breathing;
- Alpha interferon, which may help ease some symptoms associated with carcinoid syndrome;
- Steroids or theophylline, which may be prescribed for treatment of lung carcinoids;
- Antidiarrheal therapy, which may include loperamide, and;
- Diuretics, which may be used to increase urine output.
Cancerous tissue can be destroyed by using targeted liquid nitrogen or high-energy radio waves that can be injected into the area of the tumor. Ablation therapy is useful when a tumor has already spread to the liver and surgery is no longer an option.
Hepatic artery embolization
This involves the insertion of a catheter through a needle near the groin and up the main artery that supplies the blood to the liver. Through the catheter, the blood supply to the tumor in the liver can be stopped.
Chemotherapy may be used when tumors cannot be removed with surgery. Chemotherapy medication can either be taken orally or by injection.
In cases where the tumor has spread to the liver and surgery is not an option, a direct injection of the chemotherapeutic substance into the artery that supplies the liver can deliver a high dose of the medication directly to the liver, without having to expose the entire body to it.
If the cancer has spread to the bones, radiation can prove effective in alleviating bone pain, but it is not very effective in reducing the size or further spread of the tumor.
Lifestyle changes that can ease the symptoms of carcinoid syndrome include:
- Avoiding triggers that cause flushing and other symptoms, such as foods high in tyramine. These can include (but are not limited to) cheeses, cured meats, fermented foods (such as kimchi or sauerkraut), pickles, sourdough, Vegemite, tap beers and other yeast products, chocolate, fava beans, fish sauce, shrimp paste, soy sauce, bananas, pineapples, coconuts, avocado and foods that have been left to age or left out of the refrigerator;
- Avoiding large meals;
- Avoiding alcohol, and;
- Taking recommended dietary supplements to replace the nutrients lost from diarrhea.
- Bowel obstruction - cancer that spreads to the lymph nodes next to the small intestine can cause narrowing and kinking of the intestine, leading to a bowel obstruction;
- Carcinoid heart disease - a heart valve problem that can cause the valves around your heart to thicken and not function properly;
- Increased risk of falls from low blood pressure;
- Bleeding into the digestive tract, and;
- Carcinoid crisis - people with carcinoid syndrome may experience a carcinoid crisis, which can either occur without any apparent cause, or be induced by stress. The symptoms of a crisis may include severe hypertension or hypotension, irregular rapid heartbeat, wheezing, shortness of breath and prolonged flushing. A carcinoid crisis can prove life-threatening and requires careful medical attention.
The outlook for people with carcinoid syndrome depends on the size, spread and location of the underlying carcinoid tumors. New medication and therapies are helping to improve the outcome for people with carcinoid syndrome.
Early detection of carcinoid tumors reduces the risk of developing carcinoid syndrome.
- Modlin, Irvin M., Mark Kidd, Igor Latich, Michelle N. Zikusoka, and Michael D. Shapiro. “Current Status of Gastrointestinal Carcinoids.” Gastroenterology 128, no. 6 (May 2005): 1717–51.
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FAQ Frequently asked questions
What is carcinoid syndrome?
Carcinoid syndrome is a set of symptoms that are caused by an underlying carcinoid tumor of the neuroendocrine cells.
What are the symptoms of carcinoid syndrome?
Carcinoid syndrome may not show any symptoms. When they do occur, symptoms commonly include: flushing; diarrhea; wheezing and bronchospasms; heart palpitations; stomach cramps, and; low blood pressure.
What causes carcinoid syndrome?
The symptoms associated with carcinoid syndrome are due to underlying cancerous tumors of the neuroendocrine tissue, which release hormones into the bloodstream in response to chemical signals sent from the nervous system.
How is carcinoid syndrome diagnosed?
Diagnosis of carcinoid syndrome is based on measuring either the urine or blood levels of 5-hydroxyindoleacetic acid (an acid produced during the breakdown of serotonin), and imaging tests to identify the location and size of the underlying cancerous …
How is carcinoid syndrome treated?
The primary treatment for carcinoid syndrome is surgical removal of the tumor. Other treatments may include ablation, chemotherapy and medication to ease the symptoms.
Can carcinoid syndrome be cured?
In some cases, complete removal of the underlying tumor is possible. For some people, by the time they have developed symptoms of carcinoid syndrome, the underlying tumor has spread too far for complete remission to be achieved.
What is the outlook for carcinoid syndrome?
Early diagnosis of carcinoid syndrome can dramatically improve the outcome, but it will vary depending on the size, location and spread of the carcinoid tumor.
What increases the chances of developing carcinoid syndrome?
Risk factors for carcinoid syndrome may include: having a family history of the syndrome, called multiple endocrine neoplasia type 1 (MEN1); having neurofibromatosis, von Hippel-Lindau syndrome or tuberous sclerosis, or; having a …