What Causes Carcinoid Syndrome?
Carcinoid syndrome occurs when carcinoid tumors overproduce hormones and other substances that normally circulate throughout your body. One such substance that is overproduced is serotonin — one of the body's natural chemical messengers. When excess serotonin reaches tissues in the gastrointestinal tract, the lungs, or the skin, it causes the symptoms of carcinoid syndrome.
Carcinoid tumors often do not produce noticeable symptoms until they spread to the liver. It's easy to understand why, if you know that most of the blood circulation from the gastrointestinal tract must pass through the liver before it reaches the rest of the body. The liver has strong enzymes that break down and neutralize most of the excess serotonin and other substances produced by the carcinoid tumors, preventing them from reaching tissues where they can cause symptoms. When carcinoid tumors metastasize to the liver, the substances they overproduce can more easily reach your blood stream, and reach tissues where they can cause symptoms.
If you understand the role of serotonin in causing your symptoms, it is also easy to understand how an important diagnostic test for carcinoid syndrome works. Serotonin breaks down into smaller parts, called metabolites. The most important serotonin metabolite is 5-HIAA (5-hydroxyindole acetic acid). The 5-HIAA test measures the amount of this metabolite in your blood, and can therefore be used to estimate the extent of your disease.
