A physician-validated, board-style question from the Active Transport QBank. Try it, then check the reasoning for every option.
A 40-year-old man comes to the physician because of a 5-month history of watery diarrhea and episodic crampy abdominal pain. He has no fever, nausea, or vomiting. Over the past 6 months, he has had a 1.8-kg (4-lb) weight loss, despite experiencing no decrease in appetite. His wife has noticed that sometimes his face and neck become red after meals or when he is in distress. A year ago, he was diagnosed with asthma. He has hypertension. Current medications include an albuterol inhaler and enalapril. He drinks one beer daily. His temperature is 36.7°C (98°F), pulse is 85/min, and blood pressure is 130/85 mm Hg. The lungs are clear to auscultation. A grade 2/6 systolic murmur is heard best at the left sternal border and fourth intercostal space. The abdomen is soft, and there is mild tenderness to palpation with no guarding or rebound. The remainder of the physical examination shows no abnormalities. A complete blood count is within the reference range. Without treatment, this patient is at greatest risk for which of the following conditions?
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A
AsphyxiaIncorrect. Asphyxia would be from acute upper airway obstruction or severe anaphylaxis. While carcinoid can cause bronchospasm, life-threatening asphyxia is not the predominant untreated outcome.
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B
AchlorhydriaIncorrect. Achlorhydria is associated with autoimmune (pernicious anemia) or atrophic gastritis, or chronic PPI use - not with carcinoid syndrome.
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C
DementiaCorrect. Carcinoid tumors divert tryptophan to serotonin synthesis, depleting niacin precursor and producing pellagra (diarrhea, dermatitis, dementia). The greatest untreated risk for this patient is dementia from niacin deficiency.
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D
Intestinal fistulaIncorrect. Intestinal fistulas are characteristic of Crohn disease (transmural inflammation), not carcinoid tumors, which are well-circumscribed neuroendocrine tumors.
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E
HypoglycemiaIncorrect. Hypoglycemia is associated with insulinoma, which causes Whipple triad and confusion but does not produce flushing, diarrhea, or a tricuspid murmur — features that point to carcinoid syndrome instead.
↑ Tap an answer to reveal the reasoning
Answer: C. Chronic watery diarrhea with crampy abdominal pain, flushing (facial/neck redness with meals or emotional triggers), wheezing (asthma diagnosis a year ago), a right-sided heart murmur (the systolic murmur at the left sternal border in the fourth intercostal space is the location for the tricuspid valve), and unintentional weight loss describes carcinoid syndrome from a metastatic neuroendocrine (carcinoid) tumor. The classic tetrad is flushing, diarrhea, bronchospasm/asthma-like wheezing, and right-sided cardiac valvulopathy.
Carcinoid tumors arise from enterochromaffin cells, typically in the small intestine (terminal ileum is most common), appendix, or rectum. Tumors confined to the GI tract usually don't cause systemic symptoms because the liver metabolizes 5-HT and other vasoactive substances on first pass. Once the tumor metastasizes to the LIVER, hormones (especially serotonin) bypass hepatic metabolism via hepatic vein drainage and produce systemic carcinoid syndrome.
Carcinoid tumors massively use tryptophan to synthesize serotonin (~70% of dietary tryptophan diverted in advanced disease). Tryptophan is also the precursor of NIACIN (vitamin B3) via the kynurenine pathway. When tryptophan is depleted by the tumor, niacin synthesis falls, producing PELLAGRA: the classic triad of the 3 D's - Diarrhea (which the patient already has from carcinoid), DERMATITIS (photosensitive rash, particularly Casal's necklace), and DEMENTIA (cognitive decline, encephalopathy). Without treatment for the carcinoid (somatostatin analogs like octreotide, hepatic resection of metastases), this patient is most at risk for DEMENTIA.
Distractors fit other conditions:
- Asphyxia would be from anaphylaxis or severe asthma, not classical carcinoid
- Achlorhydria is associated with autoimmune gastritis, atrophic gastritis, or PPI use - not carcinoid
- Intestinal fistulas are characteristic of Crohn disease, not carcinoid
**Why each option:**
**A.** Asphyxia would be from acute upper airway obstruction or severe anaphylaxis. While carcinoid can cause bronchospasm, life-threatening asphyxia is not the predominant untreated outcome.
**B.** Achlorhydria is associated with autoimmune (pernicious anemia) or atrophic gastritis, or chronic PPI use - not with carcinoid syndrome.
**C.** Correct. Carcinoid tumors divert tryptophan to serotonin synthesis, depleting niacin precursor and producing pellagra (diarrhea, dermatitis, dementia). The greatest untreated risk for this patient is dementia from niacin deficiency.
**D.** Intestinal fistulas are characteristic of Crohn disease (transmural inflammation), not carcinoid tumors, which are well-circumscribed neuroendocrine tumors.