Q-Bank Breakdown: Celiac disease — Why Every Answer Choice Matters

You just finished a GI q-bank question and felt good… until you realized you couldn’t clearly explain why every other option was wrong. That’s the difference between pattern recognition and Step-ready clinical reasoning. Let’s do a classic celiac disease vignette and then dissect each distractor the way test writers expect you to.

Tag: GI > Intestinal Disorders

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The Clinical Vignette (Q-bank style)

A 26-year-old woman presents with 8 months of bloating, intermittent diarrhea, and fatigue. She has unintentionally lost 10 lb. She notes symptoms are worse after pasta and “bready foods.” Exam shows pallor and a pruritic, grouped vesicular rash on the extensor surfaces of her elbows. Labs: hemoglobin 9.8 g/dL, MCV 72 fL, ferritin low. CMP shows mildly elevated AST/ALT. Stool studies are negative for ova/parasites and bacterial pathogens.

Which of the following is the most likely underlying pathophysiology?

A. Autoimmune destruction of parietal cells leading to achlorhydria and impaired iron absorption
B. IgA antibodies against tissue transglutaminase leading to villous atrophy in the proximal small intestine
C. Infection with Tropheryma whipplei causing PAS-positive foamy macrophages in the lamina propria
D. Loss of enteric neurons in the distal colon causing failure of relaxation of the internal anal sphincter
E. Transmural inflammation with noncaseating granulomas affecting the terminal ileum

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Correct Answer: B. IgA antibodies against tissue transglutaminase leading to villous atrophy in the proximal small intestine

Why this is celiac disease

This vignette stacks multiple high-yield celiac clues:

• Malabsorption symptoms: chronic diarrhea, bloating, weight loss
• Iron deficiency anemia: microcytosis + low ferritin
  • Iron is absorbed primarily in the duodenum/proximal jejunum, which is classically hit in celiac
• Dermatitis herpetiformis: pruritic grouped vesicles on extensor surfaces
• Mild transaminitis: can be seen in untreated celiac (“celiac hepatitis”)
• Food trigger history: worse after gluten-containing foods

Pathophysiology (Step 1 + Step 2 framing)

• Gluten (specifically gliadin) is deamidated by tissue transglutaminase (tTG) in the intestinal mucosa.
• Deamidated gliadin binds HLA-DQ2 or HLA-DQ8 on APCs → activates T cells → inflammatory damage.
• Leads to:
  • Villous atrophy
  • Crypt hyperplasia
  • Increased intraepithelial lymphocytes (IELs)

Best tests to know (and the “gotcha”)

• First-line serology: IgA anti-tTG
• Confirmatory test: Small bowel biopsy (duodenum) showing villous atrophy/crypt hyperplasia/IELs
• Important pitfall: Selective IgA deficiency
  • If suspected (or serology negative but suspicion high), check total IgA and use IgG-based tests (e.g., IgG anti-deamidated gliadin peptide)

Key associations

• Dermatitis herpetiformis: IgA deposition in dermal papillae
• Complications:
  • Enteropathy-associated T-cell lymphoma
  • Small bowel adenocarcinoma
  • Osteopenia/osteoporosis (vitamin D malabsorption)
• Treatment:
  • Gluten-free diet
  • Dermatitis herpetiformis symptom control: dapsone (plus gluten-free diet for long-term control)

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Now the Real Test Skill: Why Each Distractor is Wrong

A. Autoimmune destruction of parietal cells leading to achlorhydria and impaired iron absorption

What this is actually describing: Autoimmune metaplastic atrophic gastritis → pernicious anemia risk.

Why it’s wrong here

• Parietal cell destruction → ↓ intrinsic factor → vitamin B12 deficiency → macrocytic anemia, neurologic findings possible.
• The vignette has microcytic anemia (MCV 72) and classic gluten-related symptoms + dermatitis herpetiformis.
• While achlorhydria can affect iron absorption, the board-style, unifying diagnosis here is proximal small bowel mucosal disease, not primary gastric autoimmunity.

High-yield contrast

• Celiac: microcytic (iron), low ferritin, duodenal pathology
• Pernicious anemia: macrocytic, anti–intrinsic factor/anti-parietal cell antibodies, neurologic signs, gastric cancer risk

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C. Infection with Tropheryma whipplei causing PAS-positive foamy macrophages in the lamina propria

What this is actually describing: Whipple disease

Why it’s wrong here

• Whipple typically presents with:
  • Weight loss + diarrhea (can mimic celiac), but also
  • Migratory arthralgias (often prominent)
  • Neurologic symptoms (cognitive changes, ophthalmoplegia)
  • Lymphadenopathy
  • Sometimes hyperpigmentation
• Histology: PAS-positive macrophages in lamina propria and acid-fast negative (classic board pairing).

This vignette instead gives:

• Dermatitis herpetiformis (very celiac-specific)
• Iron deficiency anemia without systemic infection clues

Step pearl: If the stem mentions PAS-positive macrophages + arthralgias + diarrhea → think Whipple, not celiac.

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D. Loss of enteric neurons in the distal colon causing failure of relaxation of the internal anal sphincter

What this is actually describing: Hirschsprung disease

Why it’s wrong here

• Hirschsprung is a congenital aganglionic megacolon:
  • Failure of neural crest migration → absence of Meissner and Auerbach plexuses
  • Presents in newborns/infants with:
    • Failure to pass meconium
    • Abdominal distension
    • Bilious vomiting
  • Associated with Down syndrome
• The vignette is an adult with malabsorption and dermatitis herpetiformis—totally different clinical territory.

High-yield hallmark: Explosive stool after rectal exam + transition zone on imaging + rectal biopsy without ganglion cells.

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E. Transmural inflammation with noncaseating granulomas affecting the terminal ileum

What this is actually describing: Crohn disease

Why it’s wrong here Crohn can absolutely cause diarrhea and weight loss—but look at the mismatch:

• Location: Crohn classically involves terminal ileum and colon (though it can be anywhere mouth→anus).
  • Ileal disease more commonly leads to B12 deficiency and bile salt malabsorption (watery diarrhea), not classic isolated iron deficiency from duodenal involvement.
• Path: transmural inflammation → fistulas, strictures, creeping fat; granulomas may be present.
• Extraintestinal: erythema nodosum, uveitis, arthritis (dermatitis herpetiformis is not typical).

The rash described is a huge clue:

• Dermatitis herpetiformis = celiac until proven otherwise.

High-yield contrast table

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Ultra–High-Yield Celiac Facts (Stuff USMLE Loves)

1) Antibodies and what they mean

• IgA anti-tTG: best screening test
• IgA anti-endomysial: very specific
• Anti-deamidated gliadin: useful, especially IgG if IgA deficiency

2) Biopsy findings (say it in one breath)

Villous atrophy + crypt hyperplasia + increased intraepithelial lymphocytes in the duodenum.

3) Why iron deficiency shows up early

The damage is most prominent in the proximal small intestine, where iron is absorbed.

4) Dermatitis herpetiformis link

• Deposition of IgA in dermal papillae
• Treat with gluten-free diet; dapsone helps with rash symptoms.

5) The “negative serology” trap

If suspicion is high and IgA anti-tTG is negative:

• Check total IgA
• Consider IgG deamidated gliadin or proceed to biopsy based on pretest probability

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How to Use This on Test Day (the mental checklist)

When you see chronic diarrhea + weight loss, ask:

1. Is there a nutrient-specific deficiency? (iron vs B12 vs fat-soluble vitamins)
2. Where is that nutrient absorbed? (duodenum vs ileum)
3. Any signature extra findings? (dermatitis herpetiformis screams celiac)
4. Which answer choice names the mechanism + location correctly? (anti-tTG + villous atrophy in proximal small bowel)

That’s how you stop “recognizing” celiac and start proving it—and just as importantly, proving everything else wrong.