Carcinoid Syndrome - Clinical Presentation

Clinical Presentation

The carcinoid syndrome occurs in approximately 5% of carcinoid tumors and becomes manifest when vasoactive substances from the tumors enter the systemic circulation escaping hepatic degradation. This is the case when carcinoid tumors metastasize to the liver or they arise for example in the bronchus.

The most important clinical finding is flushing of the skin, usually of the head and the upper part of thorax. Secretory diarrhea and abdominal cramps are also characteristic features of the syndrome. When the diarrhea is intensive it may lead to electrolyte disturbance and dehydration. Other associated symptoms are nausea, and vomiting. Bronchoconstriction, which may be histamine-induced, affects a smaller number of patients and often accompanies flushing.

About 50% of patients have cardiac abnormalities, caused by serotonin-induced fibrosis of the tricuspid and pulmonary valves, called cardiac fibrosis. Elevated levels of circulating serotonin have been associated with cardiac failure, due to fibrous deposits on the endocardium. These deposits are thought to be responsible for the fibrous degeneration of the valve apparatus. "TIPS" is an acronym for Tricuspid Insufficiency, Pulmonary Stenosis (fibrosis of tricuspid and pulmonary valves).

Abdominal pain is due to desmoplastic reaction of the mesentery or hepatic metastases.

Although the most common site of a carcinoid tumor is the appendix or terminal ileum, liver metastases, releasing serotonin directly into the systemic circulation are required for the carcinoid syndrome to occur. This is because serotonin created by a GI carcinoid tumour and released into the hepatic portal system is broken down at the liver and does not reach the systemic circulation. Serotonin is also metabolized in the lungs. However: If the tumor is bronchogenic in origin, then metastasis does not need to occur in order for carcinoid syndrome to occur.