✅ Model Answer:
• Diagnosis: Crohn disease (inflammatory bowel disease).
• Evidence: Elevated fecal calprotectin, elevated CRP, oral aphthous ulcers, perianal fistula, weight loss, hypoalbuminemia, negative celiac serology, normal fecal elastase.
• Next step: Esophagogastroduodenoscopy (EGD) and ileocolonoscopy with biopsies to confirm granulomas and skip lesions. Start exclusive enteral nutrition (EEN) or corticosteroids for induction. Consider biologics (infliximab) for fistulizing disease.

✅ Model Answer:
• Definition: Chronic, relapsing, transmural inflammation of the gastrointestinal tract (can affect any part from mouth to anus).
• Pathogenesis: Dysregulated immune response to gut microbiota in genetically susceptible individuals (NOD2/CARD15 mutations).
• Histology: Transmural inflammation, skip lesions, non-caseating granulomas, fissures, and fistulas.
• Location: Most commonly affects the terminal ileum and colon, but can involve any part of the GI tract.
• Extra-intestinal manifestations: Arthritis, erythema nodosum, pyoderma gangrenosum, uveitis, primary sclerosing cholangitis.

✅ Model Answer:
• GI features:
- Chronic diarrhea: May be bloody or non-bloody.
- Abdominal pain: Colicky, often in the right lower quadrant.
- Weight loss, failure to thrive.
- Nausea, vomiting.
- Perianal disease: Fistulas, abscesses, skin tags (common in children).
- Oral aphthous ulcers.
- Growth delay, delayed puberty.
• Extra-intestinal features:
- Arthritis: Peripheral or axial.
- Skin: Erythema nodosum, pyoderma gangrenosum.
- Eyes: Uveitis, episcleritis.
- Liver: Primary sclerosing cholangitis (PSC).
- Anemia: Iron deficiency or anemia of chronic disease.
- Hypoalbuminemia.

✅ Model Answer:
• Endoscopy:
- Ileocolonoscopy with biopsies: Gold standard – shows skip lesions, aphthous ulcers, cobblestoning, strictures.
- EGD: To evaluate upper GI involvement.
• Imaging:
- CT enterography or MR enterography: For small bowel evaluation, strictures, fistulas, and abscesses.
• Laboratory:
- Fecal calprotectin: >250 μg/g (sensitive for intestinal inflammation).
- CRP, ESR: Elevated.
- Complete blood count: Anemia (iron deficiency or chronic disease).
- Albumin: Low (protein-losing enteropathy).
- Anti-tTG IgA: To rule out celiac disease.
- Fecal elastase: Normal (excludes pancreatic insufficiency).
• Genetics: NOD2/CARD15 testing (not routinely used).

✅ Model Answer:
• Induction therapy:
- Exclusive enteral nutrition (EEN): First-line in children (liquid formula for 6-8 weeks) – highly effective, promotes mucosal healing.
- Corticosteroids: Prednisone 1-2 mg/kg/day (if EEN is not tolerated) – taper over 2-3 months.
- Biologics: Infliximab (anti-TNF) for moderate-severe disease, fistulizing disease, or steroid-refractory disease.
• Maintenance therapy:
- Immunomodulators: Azathioprine, 6-mercaptopurine, or methotrexate.
- Biologics: Adalimumab or infliximab (maintenance).
- 5-ASA agents: Mesalamine (limited efficacy in Crohn disease).
• Nutritional support:
- Calorie supplementation.
- Iron, calcium, vitamin D, B12, zinc supplementation.
• Surgical: For complications (strictures, fistulas, abscesses).
• Multidisciplinary care.

✅ Model Answer:
• Intestinal:
- Strictures: Bowel obstruction.
- Fistulas: Perianal, enteroenteric, enterovesical, enterocutaneous.
- Abscesses: Intra-abdominal or perianal.
- Growth failure, delayed puberty.
- Malabsorption.
- Colorectal cancer (increased risk after 8-10 years of disease).
• Extra-intestinal:
- Anemia.
- Osteoporosis.
- Arthritis, uveitis, skin manifestations.
- Primary sclerosing cholangitis (PSC).
- Thromboembolism.
• Treatment-related:
- Immunosuppression: Increased risk of infections.
- Steroid side effects: Weight gain, hypertension, diabetes, osteoporosis.

✅ Model Answer:
• Prognosis:
- Variable: Relapsing-remitting course.
- Growth: Improves with effective treatment (EEN, biologics).
- Quality of life: Can be good with medical management.
- Surgery: Often required (30-50% within 5 years).
- Cancer risk: Requires surveillance colonoscopy after 8-10 years.
- Life expectancy: Slightly reduced but improving with new therapies.
• Long-term follow-up:
- Monitor growth.
- Monitor disease activity: Fecal calprotectin, CRP, imaging.
- Monitor nutritional status.
- Monitor for complications.
- Surveillance colonoscopy.
- Multidisciplinary care.

✅ Model Answer:
• Fecal calprotectin: A protein released by activated neutrophils in the intestinal mucosa – a marker of intestinal inflammation.
• Role:
- Screening: Elevated levels (>250 μg/g) suggest intestinal inflammation, prompting endoscopic evaluation.
- Monitoring disease activity: Correlates with endoscopic inflammation; used to monitor response to therapy.
- Predicting relapse: Rising levels may predict relapse.
• Advantages:
- Non-invasive.
- More sensitive than CRP for intestinal inflammation.
- Cost-effective.
• Limitations:
- Can be elevated in other conditions (infections, NSAID use, colorectal cancer).
- Not specific for Crohn disease (also elevated in ulcerative colitis).
• Interpretation:
- <50 μg/g: Normal.
- 50-250 μg/g: Borderline (consider repeat).
- >250 μg/g: Suggestive of IBD.