Etiology and pathogenesis
Although the exact cause of IBD remains unknown, the key role of genetic predisposition has been proven. More than 9 loci determining disease risk have been discovered. For example, a mutation in the NOD2/CARD15 gene on the 6th chromosome is responsible for a specific Crohn's disease (CD) phenotype—early onset, involvement of the ileum, and a tendency to strictures.
Pathogenesis is a cascade of reactions:
- Genetic defects increase the permeability of the intestinal mucosa.
- Trigger antigens (bacteria, viruses, allergens) penetrate the barrier.
- Immune hyperactivation occurs with massive proliferation of CD4 lymphocytes.
- Cytokine imbalance develops — pro-inflammatory factors (IL-1, IL-6, TNF$\alpha$) predominate.
- Destruction of the mucosa and underlying layers of the intestinal wall is formed.
Clinical presentation and warning signs
Suspicion of IBD arises in the presence of intestinal symptoms lasting more than 4 weeks. Typical manifestations include diarrhea (often with blood), crampy abdominal pain, and tenesmus (painful false urges, characteristic when the rectosigmoid region is involved).
In addition to intestinal manifestations, IBD is accompanied by:
- General intoxication syndrome: fever, weakness, weight loss.
- Extraintestinal symptoms: peripheral arthritis, sacroiliitis, erythema nodosum, aphthous stomatitis, uveitis, and primary sclerosing cholangitis (PSC).
Features in children: In pediatric practice, the most important "red flag" is nutritional status impairment. "Weight curve drop," linear growth retardation, delayed puberty, and bone mineralization deficiency are often the earliest signs of catastrophe, sometimes preceding intestinal symptoms.
Differences between ulcerative colitis (UC) and Crohn's disease (CD)
Differential diagnosis of these two forms is critically important, but in practice can be difficult. Differences affect the macroscopic, histological picture, and the nature of complications.
Localization and macroscopy:
- UC: Inflammation always starts in the rectum and spreads continuously upwards, remaining within the colon. The small intestine is intact.
- CD: Inflammation is discontinuous (segmental). It can affect any part of the digestive tract—from the oral cavity to the anus. Perianal lesions (fissures, fistulas, paraproctitis) are characteristic.
Morphology and histology:
- In UC, inflammation is superficial, limited only to the mucosa. Crypt abscesses, neutrophil infiltration, erosions, and pseudopolyps are observed. In remission, the intestine takes on the appearance of a "water pipe."
- In CD, inflammation is transmural in nature (penetrating all layers of the wall: mucosal, submucosal, muscular, serosal). The infiltrate is predominantly lymphocytic. A pathognomonic sign is non-caseating epithelioid granulomas. Endoscopically, the mucosa resembles "cobblestone pavement," with deep fissure ulcers and the "iceberg tip" sign.
Complications: Acute life-threatening conditions (profuse bleeding, toxic megacolon, perforation) are typical for UC. Structural disorders due to transmural inflammation—strictures, fistulas, infiltrates, and abscesses—are more characteristic of CD.
Diagnostic algorithm
The basis for verifying the diagnosis is comprehensive diagnostics:
- Laboratory evaluation: General clinical blood test (inflammation, anemia), biochemistry (C-reactive protein, hypoproteinemia), liver tests. A specific activity marker is fecal calprotectin (ideal for non-invasive monitoring).
- Immunodiagnostics: ASCA antibodies are more often elevated in Crohn's disease, and ANCA in ulcerative colitis.
- "Gold standard": Ileocolonoscopy and EGD with mandatory multiple step-biopsies. Examination of the upper parts (EGD) is strictly mandatory, as CD can affect the stomach and esophagus, which changes management tactics.
To remember the depth of the lesion: UC "burns the grass" (only superficial mucosa), CD "uproots" (transmural lesion of all layers of the wall).
Class and exam questions
Why is the physical development of a child necessarily evaluated in IBD?
Due to chronic inflammation, protein loss, and malabsorption syndrome, children develop severe nutritional deficiency, which leads to growth and puberty delay.
Which stool test most accurately reflects inflammation in the intestine?
Fecal calprotectin. This is a reliable non-invasive biomarker that correlates with the degree of inflammatory activity in the mucosa.
What else to study on this topic
- Montreal classification of IBD (E, L, B axes)
- Age-related localization features: differences between pediatric and adult patterns
- Extraintestinal manifestations of IBD (PSC, uveitis, erythema nodosum)
- Toxic colonic dilation (toxic megacolon) in UC
- Specific clinical activity indices: PUCAI and PCDAI
Master the entire topic in the Pediatrics course
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Other topics in "Chapter 7. Digestive System Diseases"
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