Celiac disease is one of those “small intestine problems” that shows up everywhere on Step 1—immunology, pathology, GI, nutrition, and even derm. If you can explain why gluten triggers villous atrophy and how that translates into malabsorption + autoimmune associations, you’ll pick up a ton of easy points.
Big Picture (Step 1 Frame)
Celiac disease = immune-mediated enteropathy triggered by gluten (specifically gliadin) in genetically susceptible patients (HLA-DQ2 and HLA-DQ8). The key pathology is villous atrophy in the proximal small bowel → malabsorption.
First Aid cross-reference: GI Pathology → Celiac disease (gluten-sensitive enteropathy); Immunology → Hypersensitivity/autoimmunity associations; Derm → Dermatitis herpetiformis.
Definition & Core Mechanism
What it is
A chronic autoimmune disorder where ingestion of gluten (wheat, barley, rye) leads to T-cell–mediated damage of the small intestinal mucosa.
What “gluten” means for boards
- Gluten contains gliadin, the immunogenic component.
- Oats are often discussed—pure oats may be tolerated, but contamination is common (real-world nuance; Step tends to emphasize wheat/barley/rye).
Pathophysiology (High-Yield Step Chain)
Stepwise mechanism you should be able to recite
- Gliadin reaches small bowel mucosa.
- Tissue transglutaminase (tTG) deamidates gliadin peptides.
- Deamidated gliadin binds strongly to HLA-DQ2 or HLA-DQ8 on APCs.
- Activates CD4+ T cells → inflammatory cytokines → mucosal injury.
- Results in:
- Villous atrophy
- Crypt hyperplasia
- Increased intraepithelial lymphocytes (classically CD8+)
Why proximal small bowel matters
Damage is classically worst in the duodenum/proximal jejunum → early deficiencies:
- Iron deficiency (duodenum) → microcytic anemia
- Folate deficiency (proximal jejunum) → macrocytosis (B12 is more ileal, so less classic early)
Histology & Gross: What You’re “Seeing”
Classic biopsy findings (very testable)
- Villous atrophy (blunting)
- Crypt hyperplasia
- Intraepithelial lymphocytosis
- Inflammation in lamina propria
Quick comparison table (Celiac vs other villous issues)
| Condition | Trigger | Location | Histology clue | Key associations |
|---|---|---|---|---|
| Celiac disease | Gluten (gliadin) | Duodenum/prox jejunum | Villous atrophy + crypt hyperplasia + ↑ IELs | HLA-DQ2/DQ8, dermatitis herpetiformis, T1DM |
| Tropical sprue | Infectious (post-travel) | Entire small bowel | Villous blunting (less specific) | Improves with antibiotics + folate |
| Whipple disease | Tropheryma whipplei | Small bowel | PAS+ foamy macrophages | Arthralgias, neuro, cardiac |
Clinical Presentation (How It Shows Up on NBME)
Classic GI features
- Chronic diarrhea (often bulky/greasy from fat malabsorption)
- Steatorrhea
- Weight loss
- Abdominal pain, bloating, flatulence
Malabsorption consequences (high-yield)
- Iron deficiency anemia (most common)
- Folate deficiency → macrocytosis
- Vitamin D deficiency → osteopenia/osteomalacia, fractures
- Hypocalcemia (secondary to low vitamin D)
- Failure to thrive in children
- Easy bruising (vitamin K deficiency—less commonly emphasized but fair game)
Dermatitis herpetiformis (super high-yield association)
- Intensely pruritic, grouped vesicles/papules on extensor surfaces (elbows, knees, buttocks)
- Path: IgA deposition at dermal papillae
- Often improves with gluten-free diet; can treat symptoms with dapsone
First Aid cross-reference: Derm → Dermatitis herpetiformis and IgA deposition.
HY Associations (Autoimmune & More)
Genetic & autoimmune clustering
Celiac disease is strongly associated with:
- HLA-DQ2 and HLA-DQ8
- Type 1 diabetes mellitus
- Autoimmune thyroid disease (Hashimoto)
- Selective IgA deficiency (important for testing strategy—see diagnosis)
Malignancy risk (board-relevant)
- Increased risk of enteropathy-associated T-cell lymphoma (EATL)
- Increased risk of small bowel adenocarcinoma
Clue in vignettes: longstanding celiac + new weight loss, abdominal pain, B symptoms, or obstruction symptoms.
Diagnosis (Step-Friendly Algorithm)
Best initial test (typical patient)
Serology: IgA anti–tissue transglutaminase (anti-tTG)
Often paired with:
- Total IgA level (to rule out IgA deficiency)
If IgA deficient
Use IgG-based tests, such as:
- IgG anti–deamidated gliadin peptide (DGP)
- Sometimes IgG anti-tTG (varies by lab; DGP is commonly tested in question banks)
Confirmatory test
Small bowel biopsy (duodenal biopsy):
- Villous atrophy, crypt hyperplasia, ↑ intraepithelial lymphocytes
Critical testing pitfall
Do not start a gluten-free diet before serology/biopsy in test questions unless explicitly stated—removing gluten can normalize antibodies and improve histology → false negatives.
Antibodies: Know What They Mean
| Antibody | What it targets | Use |
|---|---|---|
| IgA anti-tTG | Tissue transglutaminase | Best screening test in most patients |
| IgA anti-endomysial | Endomysium (related to tTG) | Highly specific; sometimes used for confirmation |
| Anti-deamidated gliadin (DGP) | Deamidated gliadin peptides | Helpful esp. in IgA deficiency or some pediatric cases |
Board phrase translation: “anti-endomysial” and “anti-tTG” are the classic celiac antibodies; gliadin becomes higher yield when they want you to think about tTG deamidation.
Treatment (What Actually Helps)
Mainstay
- Strict lifelong gluten-free diet (wheat, barley, rye avoidance)
- Nutritional repletion as needed:
- Iron
- Folate
- Calcium + vitamin D
- Others depending on deficiencies
Dermatitis herpetiformis
- Gluten-free diet (long-term control)
- Dapsone (symptomatic relief)
Follow-up concept (common in vignettes)
If symptoms persist despite gluten-free diet, consider:
- Ongoing gluten exposure (most common)
- Alternate diagnosis or complication (e.g., lymphoma)
- Refractory celiac disease (less common; more advanced topic)
High-Yield “Tell Me It’s Celiac” Clues
- Chronic diarrhea + weight loss + iron deficiency anemia
- Dermatitis herpetiformis on extensor surfaces
- Positive IgA anti-tTG
- Biopsy: villous atrophy + crypt hyperplasia + increased intraepithelial lymphocytes
- Association with HLA-DQ2/DQ8 and other autoimmune diseases
Common NBME-Style Traps & How to Avoid Them
Trap 1: IgA deficiency → negative IgA anti-tTG
If they mention recurrent giardia/resp infections or explicitly “IgA deficiency,” don’t be fooled by a negative IgA test—go to IgG DGP (and/or IgG tTG).
Trap 2: Confusing celiac with lactose intolerance
- Lactose intolerance = osmotic diarrhea, bloating after dairy; not autoimmune; no villous atrophy pattern as primary cause.
- Celiac can cause secondary lactose intolerance because brush border damage decreases lactase—so dairy intolerance can show up after celiac.
Trap 3: Celiac vs IBD
- Celiac: malabsorption, nutrient deficiencies, improvement with diet, small bowel villous changes.
- IBD: inflammatory diarrhea often with blood (esp UC), extraintestinal manifestations, different histology patterns.
Rapid Review (Last-Minute Checklist)
- Etiology: Gluten (gliadin) → tTG deamidation → HLA-DQ2/DQ8 presentation → T-cell–mediated injury
- Location: Proximal small bowel
- Biopsy: Villous atrophy + crypt hyperplasia + ↑ intraepithelial lymphocytes
- Serology: IgA anti-tTG (check total IgA); IgG DGP if IgA deficient
- Associations: Dermatitis herpetiformis (IgA at dermal papillae), T1DM, autoimmune thyroid disease
- Complications: EATL, small bowel adenocarcinoma
- Tx: Gluten-free diet; replace deficiencies; dapsone for dermatitis herpetiformis