Most people with carcinoid tumors have symptoms similar to those of other intestinal cancers, mainly cramping pain and changes in bowel movements as a result of obstruction. The most common and often the earliest symptom of carcinoid syndrome is an uncomfortable flushing, typically of the head and neck. The flushing is thought to be caused by excess histamine and bradykinin, which dilate blood vessels. Flushing is often triggered by emotions, by eating, or by drinking alcohol or hot liquids. Excess serotonin triggers the muscles around the intestines to contract, causing diarrhea, cramping, and malabsorption of foods.
Malabsorption leads to malnutrition and produces fatty, very foul-smelling stools in some people.
Carcinoid syndrome can damage the heart and lungs. Whether serotonin is the only substance involved and how the body produces the fibrous material are both unknown. To help make the diagnosis, a doctor sometimes gives drugs such as calcium gluconate, catecholamines, pentagastrin, or alcohol to provoke flushing. However, because provocative tests can cause uncomfortable and sometimes serious symptoms, they are done only under close observation in a hospital. A CT or MRI scan can help determine whether the tumor has spread to the liver.