A physician-validated, board-style question from the Active Transport QBank. Try it, then check the reasoning for every option.
A previously healthy 29-year-old man comes to the emergency department because of a 4-day history of abdominal pain and confusion. Prior to the onset of the abdominal pain, he visited a festival where he consumed large amounts of alcohol. Examination shows a distended abdomen, decreased bowel sounds, and diffuse tenderness to palpation. There is motor weakness in the upper extremities. Sensation is decreased over the upper and lower extremities. Laboratory studies show no abnormalities. Which of the following is the most appropriate therapy for this patient's condition?
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A
Intravenous immunoglobulinIncorrect. IVIG is treatment for Guillain-Barré syndrome — which can cause neuropathy but lacks the abdominal pain, mental status changes, and alcohol-precipitation of an AIP attack.
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B
HeminCorrect. Hemin (heme arginate) suppresses ALA synthase via negative feedback, rapidly shutting down porphyrin precursor accumulation and aborting the acute attack.
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C
Ethylenediaminetetraacetic acidIncorrect. EDTA is used to chelate lead in lead poisoning, which can cause abdominal pain and neuropathy but doesn't fit the alcohol-precipitated, autonomic-confused acute attack pattern.
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D
ChlordiazepoxideIncorrect. Chlordiazepoxide treats alcohol withdrawal but wouldn't address the underlying porphyric crisis — and benzodiazepines/barbiturates can actually exacerbate AIP.
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E
PyridoxineIncorrect. Pyridoxine (vitamin B6) is the antidote for isoniazid-induced neuropathy and seizures and is used in homocystinuria — it does not abort an acute porphyric crisis, which requires hemin and IV glucose.
↑ Tap an answer to reveal the reasoning
Answer: B. A previously healthy young man presents with the triad of abdominal pain, autonomic instability (suggested by altered mental status/confusion), and motor neuropathy (upper-extremity motor weakness with sensory changes) after a heavy alcohol binge — the classic presentation of an acute attack of acute intermittent porphyria (AIP). AIP is an autosomal dominant defect in porphobilinogen deaminase (hydroxymethylbilane synthase), causing accumulation of upstream porphyrin precursors (PBG, ALA). Attacks are precipitated by drugs that induce CYP450 (barbiturates, anticonvulsants, alcohol), low caloric intake (fasting, dieting), stress, infection, and hormonal fluctuations.
The mnemonic for the clinical features of AIP is the 5 Ps: Painful abdomen, Polyneuropathy, Psychological symptoms (psychosis, anxiety, confusion), Precipitated by drugs/fasting/alcohol, and Port wine-colored urine (PBG oxidizes on standing). Notably, AIP does NOT cause cutaneous photosensitivity — that's seen in porphyria cutanea tarda.
Acute attacks are treated with intravenous hemin (heme arginate) and a high-carbohydrate infusion ("glucose-loading") — both of which suppress ALA synthase, the rate-limiting enzyme, and shut down porphyrin precursor production. IVIG is for Guillain-Barré syndrome (which can mimic AIP neuropathy but lacks the abdominal pain and confusion); EDTA chelates lead (lead poisoning can cause abdominal pain and neuropathy — but no alcohol-precipitated attack); chlordiazepoxide is for alcohol withdrawal (not the mechanism here, and it would worsen AIP).
**Why each option:**
**A.** IVIG is treatment for Guillain-Barré syndrome — which can cause neuropathy but lacks the abdominal pain, mental status changes, and alcohol-precipitation of an AIP attack.
**B.** Correct. Hemin (heme arginate) suppresses ALA synthase via negative feedback, rapidly shutting down porphyrin precursor accumulation and aborting the acute attack.
**C.** EDTA is used to chelate lead in lead poisoning, which can cause abdominal pain and neuropathy but doesn't fit the alcohol-precipitated, autonomic-confused acute attack pattern.
**D.** Chlordiazepoxide treats alcohol withdrawal but wouldn't address the underlying porphyric crisis — and benzodiazepines/barbiturates can actually exacerbate AIP.