Gastroenterology · Neuroendocrine Tumors
The facts most likely to be tested
Carcinoid syndrome occurs only when neuroendocrine tumors (typically from the midgut) metastasize to the liver, allowing vasoactive substances to bypass first-pass metabolism.
The classic clinical triad consists of episodic cutaneous flushing, secretory diarrhea, and wheezing due to bronchospasm.
Chronic exposure to high levels of serotonin leads to right-sided valvular heart disease, specifically tricuspid regurgitation and pulmonic stenosis.
The diagnostic test of choice is a 24-hour urine collection for 5-hydroxyindoleacetic acid (5-HIAA), the primary metabolite of serotonin.
Pellagra (dermatitis, diarrhea, dementia) can develop because the tumor consumes tryptophan to produce serotonin, leading to a niacin (Vitamin B3) deficiency.
Octreotide, a long-acting somatostatin analog, is the first-line pharmacologic treatment to inhibit the release of vasoactive peptides.
Carcinoid crisis is a life-threatening complication characterized by severe hypotension and tachycardia that can be precipitated by anesthesia or surgical manipulation of the tumor.
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A 58-year-old male presents to the clinic with a 6-month history of recurrent facial flushing and watery diarrhea. He also reports increasing shortness of breath on exertion. Physical examination reveals a holosystolic murmur at the left lower sternal border that increases with inspiration and pedal edema. A CT scan of the abdomen demonstrates a mass in the terminal ileum with multiple hepatic lesions.
What is the most likely underlying cause of this patient's cardiac findings?
Serotonin-induced endocardial fibrosis
The patient exhibits classic signs of carcinoid syndrome; the elevated serotonin levels cause fibrous plaque deposition on the right-sided heart valves, leading to tricuspid regurgitation.
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High yield triage
Etiology / Epidemiology
Caused by neuroendocrine tumors (NETs) secreting vasoactive substances; requires liver metastasis to bypass first-pass metabolism.
Clinical Manifestations
Classic triad of flushing, diarrhea, and wheezing; pellagra-like skin changes may occur.
Diagnosis
Elevated 24-hour urine 5-HIAA is the gold standard; CT/MRI used for tumor localization.
Treatment
Octreotide is the first-line treatment; avoid triggers like alcohol or stress.
Prognosis
Risk of carcinoid heart disease (right-sided valvular fibrosis) is the primary cause of mortality.
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Epidemiology & Etiology
Most commonly arises from midgut (ileum) neuroendocrine tumors. Systemic symptoms only manifest once the tumor has metastasized to the liver, allowing serotonin to enter systemic circulation without hepatic degradation.
Pertinent Anatomy
Primary tumors are typically located in the distal ileum or appendix. Metastasis to the liver is the anatomical prerequisite for the syndrome.
Pathophysiology
Tumors secrete excess serotonin, histamine, and bradykinin. Serotonin is metabolized into 5-HIAA (5-hydroxyindoleacetic acid) by the liver and lungs. Systemic release causes vasodilation, increased gut motility, and bronchoconstriction.
Clinical Manifestations
Patients present with episodic cutaneous flushing, secretory diarrhea, and bronchospasm. Chronic serotonin excess leads to right-sided valvular heart disease (tricuspid regurgitation/pulmonary stenosis). Pellagra (dermatitis, dementia, diarrhea) occurs due to niacin deficiency as tryptophan is diverted to serotonin synthesis.
Diagnosis
The 24-hour urine 5-HIAA is the diagnostic test of choice. Serum chromogranin A is a sensitive marker for tumor burden. CT or MRI of the abdomen/pelvis is required to localize the primary tumor and assess hepatic involvement.
Treatment
Octreotide (a somatostatin analog) is the first-line therapy to inhibit hormone release. Avoid triggers such as alcohol, spicy foods, and emotional stress. Surgical debulking of liver metastases is indicated for symptomatic control.
Prognosis
Long-term monitoring requires echocardiography to screen for right-sided valvular fibrosis. Prognosis is dependent on the extent of hepatic metastasis and the ability to control hormone secretion.
Differential Diagnosis
Pheochromocytoma: episodic hypertension and palpitations
Mastocytosis: pruritus and urticaria (Darier sign)
VIPoma: watery diarrhea without flushing
Medullary thyroid cancer: elevated calcitonin
Menopause: flushing without diarrhea or heart disease