Crohn's Disease: Inflammation - Comprehensive Overview

What Is Crohn's Disease?

• Schwartz's Principles of Surgery, 11th ed. - "Crohn's disease is a transmural inflammatory process that can affect any part of the gastrointestinal tract."

Pathology and Inflammatory Features

Gross Pathology (What You See Macroscopically)

Microscopic / Histological Features

• Transmural inflammation - all layers (mucosa → serosa) involved
• Non-caseating granulomas - present in 50-60% of cases; pathognomonic when found
• Crypt abscesses and distortion
• Pyloric gland metaplasia (indicates repeated bouts of inflammation and repair)
• Submucosal fibrosis

Spread of Inflammation

• Superficial disease - mucosal/submucosal inflammation
• Advanced disease - full-thickness (transmural) involvement → adhesions, abscesses, fistulas, and rarely free perforation

Resected bowel showing the cobblestone pattern with deep ulcerations and sharp demarcation between diseased and normal mucosa - classic Crohn's disease appearance

Sigmoid colectomy specimen showing cobblestone mucosa, fissuring ulcers, creeping fat, and a colovesical fistula - consequence of transmural Crohn's inflammation

Sites of Involvement

• Schwartz's Principles of Surgery: "The disease affects the small bowel in 80% of cases and colon alone in 20%."

Clinical Presentation by Inflammation Type

1. Aggressive inflammatory disease - active mucosal and transmural inflammation
2. Fibrostenotic disease - chronic inflammation leads to fibrosis and strictures
3. Fistulizing disease - transmural inflammation erodes through to adjacent structures

Symptoms Due to Active Inflammation

• Abdominal pain (crampy, usually right lower quadrant in ileocecal disease)
• Diarrhea (>10 bowel movements/day during a flare)
• Fever
• Weight loss
• Nausea, vomiting
• Bloating
• Perianal pain, swelling, drainage (fistulas/abscesses)

"Symptoms of Crohn's disease depend on the severity of inflammation and/or fibrosis and the location of inflammation in the gastrointestinal tract. Acute inflammation may produce diarrhea, crampy abdominal pain, and fever." - Schwartz's Principles of Surgery

Measuring Disease Activity (Inflammation Severity)

Extraintestinal Manifestations of Inflammation

CD vs Ulcerative Colitis: Key Inflammatory Differences

Management of Inflammation

Medical Therapy (Step-up Approach)

• PPIs are first-line for gastric/duodenal Crohn's
• Anti-TNF therapy (infliximab) is effective for fistulizing disease and refractory luminal inflammation
• Strictures with an inflammatory component may improve with optimal medical therapy (anti-fibrotic strictures require endoscopic dilation or surgery)

Surgical Indications

• Bowel obstruction not responsive to medical management
• Intra-abdominal abscesses
• Fistulas refractory to medical therapy
• Free perforation
• Dysplasia/malignancy
• ~75% of CD patients will require at least one abdominal operation in their lifetime

Complications of Chronic Inflammation

1. Strictures - from fibrosis after transmural inflammation; cause small bowel obstruction (SBO)
2. Fistulas - enteroenteric, enterovesical (colovesical fistula → pneumaturia), enterocutaneous, rectovaginal
3. Abscesses - intra-abdominal or perianal
4. Malabsorption - protein-losing enteropathy, vitamin B12 deficiency (terminal ileum), bile acid malabsorption
5. Short bowel syndrome - after repeated surgical resections
6. Colorectal cancer - elevated risk with long-standing colonic CD

• Sleisenger and Fordtran's Gastrointestinal and Liver Disease (Crohn Disease chapters)
• Schwartz's Principles of Surgery, 11th ed. (Chapter 28)
• Maingot's Abdominal Operations (Chapters on perianal Crohn's and IBD)

Diet in Crohn's Disease

Why Nutrition Matters in Crohn's Disease

• Reduced oral intake (pain, nausea, fear of eating)
• Malabsorption (especially with ileal disease - vitamin B12, fat-soluble vitamins, bile acids)
• Protein-losing enteropathy
• Increased metabolic demands during inflammation
• Surgical bowel resections leading to short bowel

"Nutritional support in all patients with Crohn disease is paramount. Ideally, preservation of oral feeding in any form is crucial for maintenance of the absorptive and protective mechanisms provided by the GI mucosal lumen." - Mulholland and Greenfield's Surgery, 7th ed.

Dietary Therapeutic Strategies

1. Exclusive Enteral Nutrition (EEN) - First-Line in Pediatrics

• In pediatric CD: EEN has similar efficacy to oral corticosteroids for inducing clinical remission, but is more effective at achieving mucosal healing - making it the preferred first-line induction therapy in children (endorsed by NASPGHAN).
• It avoids the growth suppression caused by steroids in children.
• In adults: EEN has not shown superior benefit over corticosteroids for remission induction.
• Drawback: poor palatability, restrictive, and may reduce gut bacterial diversity (decreased Bifidobacterium, Ruminococcus, Faecalibacterium).
• Yamada's Textbook of Gastroenterology, 7th ed.; Mulholland and Greenfield's Surgery, 7th ed.

2. Crohn's Disease Exclusion Diet (CDED) + Partial Enteral Nutrition (PEN)

• Gluten
• Dairy products
• Red/processed meats
• Refined sugars and processed foods
• Emulsifiers and additives

• Sleisenger and Fordtran's GI and Liver Disease

3. CD-TREAT Diet (Crohn's Disease Treatment-with-Eating)

• Gluten
• Dairy
• Alcohol
• Refined sugars

• Yamada's Textbook of Gastroenterology, 7th ed.

4. Mediterranean Diet (MD)

• Rich in fruits, vegetables, whole grains, legumes, olive oil, fish; low in red/processed meat.
• A 2021 RCT (referenced in Harrison's Principles of Internal Medicine, 22E) compared the Specific Carbohydrate Diet (SCD) to the Mediterranean Diet in adult CD - both achieved comparable clinical remission rates.
• The Mediterranean diet is more sustainable and palatable long-term.

5. Specific Carbohydrate Diet (SCD)

• Eliminates all grains, lactose, sucrose, and processed foods; allows meats, fish, eggs, certain fruits/vegetables, and specific cheeses.
• Promising results in pediatric CD, but evidence quality is moderate.
• Referenced in Harrison's 22E and Sleisenger's GI Disease.

6. Low-FODMAP Diet

• Reduces symptoms (bloating, gas, diarrhea) in patients with quiescent or mildly active CD.
• A RCT showed 52% symptom relief vs 16% on control diet (p=0.007).
• Important caveat: Low-FODMAP reduces symptoms but its effect on actual mucosal inflammation in CD is unknown. It may also reduce Bifidobacteria and Faecalibacterium prausnitzii - beneficial gut bacteria.
• Best used for symptom management, not as primary anti-inflammatory therapy.
• Yamada's Textbook of Gastroenterology

7. High-Fiber Diet

• During acute flares with strictures or obstruction, fiber should be restricted to avoid blockage - low-residue diet is preferred during flares.

Nutritional Support: When Oral Diet Is Not Enough

"Total parenteral nutrition (TPN) was useful in patients with active Crohn disease; however, complication rates exceed those for enteral nutrition." - Sabiston Textbook of Surgery

Key Nutritional Deficiencies to Monitor and Supplement

Practical Dietary Guidance by Disease State

During Active Flare

• Low-residue / low-fiber diet - reduces stool frequency and risk of obstruction with strictures
• Avoid raw vegetables, seeds, nuts, corn, popcorn
• Small, frequent meals
• Adequate hydration
• Enteral nutrition support if oral intake is severely compromised

During Remission (Maintenance)

• Mediterranean-style diet - anti-inflammatory, sustainable, diverse
• High-fiber foods (if tolerated and no strictures) - support microbiome
• Adequate protein intake (1.2-1.5 g/kg/day) for tissue repair
• Avoid ultra-processed foods, food additives, emulsifiers, excess red meat
• Limit alcohol (mucosal irritant)
• Avoid smoking - smoking significantly worsens CD course, increases relapse rates, and increases need for surgery

Foods to Generally Avoid or Limit

• Fried/greasy foods
• Carbonated drinks
• Spicy foods (can aggravate symptoms)
• High-lactose dairy (if lactose intolerant)
• Alcohol
• Excess caffeine

Recent Evidence Summary

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