Carcinoid syndrome

A group of symptoms caused by hormone-like substances released by certain neuroendocrine tumors. Common features include episodic flushing, diarrhea, wheezing, and, over time, damage to heart valves.

Serotonin: A neurotransmitter and signaling molecule that also regulates intestinal movement and vascular function. Excess serotonin from some tumors drives diarrhea and can promote fibrotic heart-valve damage.
Neuroendocrine tumor: A neoplasm arising from cells with features of both nerve cells and hormone-secreting cells. These tumors are the source of the mediators that produce the syndrome.
Urinary 5-HIAA test: A urine test that measures 5-hydroxyindoleacetic acid, a serotonin breakdown product. It helps assess serotonin production when the syndrome is suspected.
Pheochromocytoma: A tumor of adrenal medulla or related tissue that often secretes catecholamines. Its episodic flushing and cardiovascular symptoms can resemble attacks in this syndrome.
5-Hydroxyindoleacetic acid: The principal breakdown product of serotonin, measured in blood or urine as a marker of serotonin production. Its elevated level can indicate the serotonin excess associated with this syndrome.
Enterochromaffin cell: A serotonin-producing cell found mainly in the gastrointestinal lining. Many serotonin-secreting intestinal tumors arise from this cell type.
Chromogranin A: A protein found in secretory granules of many neuroendocrine cells and tumors. Its blood concentration can support assessment of neuroendocrine tumor burden, though it is nonspecific.
Mast cell activation syndrome: A disorder involving recurrent episodes caused by release of mediators from activated mast cells. It can cause flushing, diarrhea, and wheezing through a different source of mediators.
Prostaglandins: Lipid signaling molecules that influence inflammation, smooth-muscle activity, and blood-vessel tone. Tumor-derived prostaglandins may contribute to flushing and changes in intestinal function.
Midgut: The embryonic digestive region that gives rise to much of the small intestine and the proximal colon. Midgut tumors are a common source of the classic serotonin-associated syndrome.

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