Carcinoid syndrome

What it is

Carcinoids are small, slow-growing neuroendocrine tumors. They are most located in the gastrointestinal tract, often in the small intestine, or in the lungs, and they can synthesize a variety of hormones, especially serotonin, and also bradykinin and histamine.

Most carcinoids are asymptomatic, because most of the hormones they produce are metabolized by the first-pass effect in the liver. Carcinoid syndrome may occur if a serotonin-producing tumor has metastasized to the liver, bypassing first-pass metabolism.

How it presents

The syndrome is characterized by diarrhea, flushing, dyspnea and wheezing.

• The diarrhea is intermittent, and may be bulky and foul-smelling.
• Flushing is common and episodic, red or purple, especially over the face and neck.
• Right-sided heart disease with valvular lesions belongs to the picture.
• Electrolyte abnormalities are often none, unless the diarrhea is severe.

How it is diagnosed

Elevated 5-HIAA in the urine helps to establish the diagnosis, measured as 24-hour urinary 5-HIAA, that is 5-hydroxyindoleacetic acid. Severe secretory diarrhea with flushing is the picture that should send you to that test.

Imaging techniques such as CT, MRI and somatostatin receptor scintigraphy, the octreotide scan, are used to detect the primary tumor as well as its metastases.

The syndrome to hold it against is VIPoma, the WDHA syndrome, which is an islet cell tumor secreting vasoactive intestinal peptide. VIPoma gives profuse watery diarrhea of large volume with hypokalemia, achlorhydria and metabolic acidosis, its flushing is less common and non-episodic and generalized, and heart involvement is rare. Carcinoid syndrome gives episodic flushing, wheezing and heart involvement, and often no electrolyte abnormality at all.