Flushing, diarrhea, bronchospasm, and right-sided valvular heart disease from serotonin-secreting neuroendocrine tumor with hepatic metastases.
Also known as: carcinoid syndrome, carcinoid tumor, neuroendocrine tumor, NET, carcinoid heart disease, Hedinger syndrome
Overview
Clinical syndrome caused by systemic release of vasoactive substances — predominantly serotonin (5-HT) but also histamine, tachykinins, bradykinin, and prostaglandins — from a well-differentiated neuroendocrine tumor (NET), most often arising in the midgut (jejunum, ileum, appendix, proximal colon) with hepatic metastases. Carcinoid syndrome generally occurs only after the liver loses its ability to inactivate tumor-derived mediators (i.e., with hepatic metastasis or with primary tumors that bypass portal circulation, such as bronchial or ovarian).
Epidemiology
Neuroendocrine tumors have an incidence of approximately 6.98 per 100,000 person-years in the United States, with increasing recognition. Only about 20% of patients with metastatic midgut NETs develop carcinoid syndrome. Median age at diagnosis is the sixth decade.
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Midgut NET (most likely to cause carcinoid syndrome): ileum and jejunum
Hepatic metastases (essential for typical midgut-derived syndrome)
Bronchial, thymic, or ovarian NETs (can cause syndrome without hepatic metastases due to direct systemic venous drainage)
MEN1 syndrome (foregut NETs in MEN1)
Family history of neuroendocrine or MEN-related tumors
Pathophysiology
Enterochromaffin-cell-derived neoplasms produce serotonin from tryptophan via 5-hydroxytryptophan. Under normal conditions, hepatic monoamine oxidase metabolizes portal-vein serotonin to 5-hydroxyindoleacetic acid (5-HIAA) before it reaches the systemic circulation. Once hepatic metastases or extra-portal primaries permit systemic release, serotonin and other mediators produce vasomotor (flushing, hypotension), gastrointestinal (secretory diarrhea, hypermotility), and bronchial (bronchospasm) effects. Chronic exposure to serotonin promotes fibrotic plaque deposition on right-sided cardiac valves (left-sided valves are spared because pulmonary metabolism inactivates serotonin before it reaches the left heart).
Clinical presentation
Symptoms
Episodic cutaneous flushing — dry, brick-red face and neck lasting seconds to minutes; triggered by stress, exercise, alcohol, tyramine-containing foods (aged cheese, smoked meats)
Secretory diarrhea — watery, large volume, may persist with fasting; abdominal cramping
Medullary thyroid carcinoma — Diarrhea and flushing; elevated calcitonin and CEA; consider MEN2
Inflammatory bowel disease — Diarrhea with blood or mucus, weight loss, extraintestinal manifestations; endoscopy with biopsy; normal 5-HIAA
Idiopathic flushing or alcohol-induced flushing — Triggered exposure; no other mediator-driven features; normal biochemistry
Diagnostic workup
Diagnostic criteria
Clinical syndrome (flushing, diarrhea ± bronchospasm) plus elevated 24-hour urinary 5-HIAA (typically >2-3 times upper limit of normal) and tissue confirmation of a well-differentiated neuroendocrine tumor with positive immunohistochemistry for chromogranin A and synaptophysin.
Labs
24-hour urinary 5-hydroxyindoleacetic acid (5-HIAA) — high specificity for midgut carcinoid; patient must avoid serotonin-containing foods (bananas, pineapples, kiwi, plums, walnuts, pecans, avocados, tomatoes, eggplant) and certain medications (acetaminophen, salicylates, L-dopa, SSRIs, MAOIs) for 48-72 hours before and during collection
Plasma 5-HIAA (alternative to 24-hour urine, increasing availability)
Chromogranin A — sensitive but nonspecific; falsely elevated by PPIs, renal failure, atrophic gastritis
NT-proBNP if right-sided heart failure suspected (correlates with carcinoid heart disease severity)
Niacin level if pellagra-like features present
Imaging
Triple-phase contrast-enhanced CT or MRI of abdomen and pelvis to localize primary tumor and assess hepatic metastases
68Ga-DOTATATE PET/CT — gold standard functional imaging for somatostatin receptor expression and small-volume disease
Echocardiography for carcinoid heart disease screening — recommended annually in patients with biochemically active syndrome; look for retracted, fibrotic tricuspid and pulmonic leaflets
Endoscopy and capsule endoscopy if primary not located on cross-sectional imaging
Diagnostic algorithm
Feature
Detail
Most common primary site
Midgut (ileum, jejunum) — requires hepatic metastases for syndrome
Somatostatin analog (octreotide, lanreotide) + surgery if resectable
Advanced therapy
PRRT with 177Lu-DOTATATE; telotristat for refractory diarrhea
Anesthesia preparation
Octreotide infusion to prevent carcinoid crisis
Essentials of carcinoid syndrome — diagnosis and management.
Treatment
First-line
Somatostatin analog — octreotide (short-acting 100-500 mcg SC three times daily for symptom flares; long-acting octreotide LAR 20-30 mg IM monthly for maintenance), lanreotide (depot 120 mg SC every 4 weeks) — controls flushing and diarrhea and slows tumor growth
Curative surgical resection of localized primary and resectable metastases when feasible
Cytoreductive (debulking) hepatic surgery, radiofrequency ablation, or hepatic artery embolization for symptomatic liver-dominant disease
Second-line / adjunct
Telotristat ethyl — peripheral tryptophan hydroxylase inhibitor; reduces stool frequency in carcinoid diarrhea uncontrolled by somatostatin analog
Everolimus (mTOR inhibitor), sunitinib (for pancreatic NETs), or systemic chemotherapy (capecitabine-temozolomide for select NETs)
Interferon-alfa (largely supplanted by newer therapies but historically used)
Niacin (nicotinamide) supplementation for pellagra prevention in long-standing disease
Tricuspid and pulmonary valve replacement for advanced carcinoid heart disease with right heart failure
Carcinoid crisis prophylaxis: octreotide infusion 100-500 mcg/hr beginning before induction of anesthesia or interventions in any patient with known disease
Complications
Carcinoid crisis — life-threatening hypotension, bronchospasm, arrhythmias, and altered mental status triggered by anesthesia, surgery, embolization, biopsy, or stress; treated with IV octreotide bolus and infusion (avoid catecholamines, which can worsen the crisis)
Carcinoid heart disease (Hedinger syndrome) — right-sided valvular fibrosis with tricuspid regurgitation and pulmonary stenosis leading to right heart failure
Mesenteric fibrosis and intestinal obstruction or ischemia
Niacin deficiency and pellagra (dermatitis, diarrhea, dementia)
Metastatic neuroendocrine disease — most often to liver, less commonly to bone and lung
PANCE pearls
Carcinoid syndrome from a midgut tumor essentially requires hepatic metastases — without them, serotonin is metabolized first-pass by the liver. Suspect non-hepatic primary (bronchial, ovarian) if the syndrome appears without liver disease.
Always pretreat with octreotide before anesthesia, surgery, embolization, or biopsy in any patient with known or suspected carcinoid syndrome — carcinoid crisis is preventable and frequently lethal if untreated. Do NOT use epinephrine to treat hypotension, as it can paradoxically worsen mediator release.
Carcinoid heart disease affects the RIGHT side because pulmonary endothelium metabolizes serotonin before it reaches the left heart; primary bronchial carcinoids can cause LEFT-sided disease.
24-hour urinary 5-HIAA collection requires dietary and medication restrictions for 48-72 hours — bananas, pineapples, walnuts, avocado, tomatoes, eggplant, acetaminophen, and SSRIs can cause false-positive elevations.
Tryptophan diversion into serotonin synthesis leaves insufficient substrate for niacin (vitamin B3) — supplement nicotinamide to prevent pellagra in long-standing disease.
References
NANETS 2017 — North American Neuroendocrine Tumor Society Consensus Guidelines for the Diagnosis of Neuroendocrine Tumor (Strosberg et al., Pancreas 2017)
ENETS 2016 — European Neuroendocrine Tumor Society Consensus Guidelines for the Management of Patients with Functional Pancreatic Neuroendocrine Tumors and Non-Functional Pancreatic Neuroendocrine Tumors (Falconi et al., Neuroendocrinology 2016)
Endocrine Society 2011 — Pheochromocytoma, Paraganglioma, and Other Catecholamine-Secreting Tumors (review and management context); plus AACE/AAES NET pathway statements
NETTER-1 Trial — Phase 3 Trial of 177Lu-Dotatate for Midgut Neuroendocrine Tumors (Strosberg et al., NEJM 2017)
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