Pathophysiology and Clinical Implications of Crohn's Disease

Introduction to Crohn's Disease

Crohn's disease results from an inappropriate inflammatory reaction to intestinal flora in genetically predisposed individuals, characterized by transmural granulomatous inflammation that can affect any part of the gastrointestinal tract, as noted by the American College of Radiology 1, 2

The disease is more prevalent in developed countries, suggesting environmental influences play a significant role in disease development, according to the American Academy of Allergy, Asthma, and Immunology 3

The inflammation in Crohn's disease is transmural (affecting all layers of the bowel wall) and granulomatous in nature, characterized by discontinuous or "skip" lesions that can occur anywhere in the gastrointestinal tract, as described by the American College of Radiology 2, 4
The inflammatory process leads to progressive structural damage over time with recurrent bouts of inflammation, resulting in stricture formation, penetrating sinuses, or fistulas, as reported by the American College of Radiology 2, 4

Any portion of the gastrointestinal tract may be involved, with the small bowel alone affected in about one-third of patients, the colon alone in a somewhat higher percentage, and combined involvement in less than one-third, according to the American College of Radiology 4
Perianal disease is another common manifestation, occurring in 15-25% of pediatric patients, as noted by the American College of Radiology 2
In children, there is an inverse relationship between age and colonic involvement - younger patients are more likely to have colonic disease, as reported by the European Crohn's and Colitis Organisation 5, 6
Pediatric patients are more likely to have upper gastrointestinal involvement than adults, according to the European Crohn's and Colitis Organisation 5, 6

The transmural nature of inflammation explains complications like fistulas, abscesses, and strictures that are characteristic of Crohn's disease, as described by the American College of Radiology 2, 4

The diagnosis of Inflammatory Bowel Disease (IBD) can evolve over time, with endoscopy combined with other diagnostic modalities able to differentiate Crohn's Disease (CD) from Ulcerative Colitis (UC) in 85% of patients, although the diagnosis may change over time, according to the European Crohn’s and Colitis Organisation 7
In a prospective study of over 350 patients with IBD followed for more than 22 months, the IBD diagnosis was revised in 4% of cases, highlighting the importance of ongoing evaluation, as recommended by the European Crohn’s and Colitis Organisation 8

Upper GI endoscopic lesions suggestive of Crohn's disease include focally active gastritis in the absence of Helicobacter pylori, which can be identified through upper GI endoscopy, as suggested by the American Gastroenterological Association 7, 8
Recent studies show that 18.1% of CD patients may have concurrent infections, emphasizing the need to rule out infectious causes, according to the American Gastroenterological Association 9

The uneven distribution of inflammation can occur in patients with long-standing disease or after treatment, which may lead to complications such as strictures or penetrating disease, as noted by the European Crohn’s and Colitis Organisation 10
Rectal sparing occurs in more than 3% of Ulcerative Colitis patients, so the absence of rectal disease does not definitively indicate CD over UC, according to the European Crohn’s and Colitis Organisation 10