Inflammatory Bowel Disease II: Crohn's Disease

Crohn's disease can affect any segment of the GI tract from the mouth to the anus, but most commonly impacts the distal ileum and ascending colon. The disease is characterized by transmural inflammation, meaning it affects all layers of the bowel wall rather than just the surface. This transmural involvement distinguishes Crohn's disease from other inflammatory conditions and contributes to its severity and complications.

Crohn's disease inflammation begins with infiltration around an intestinal crypt, progressing to small focal ulcers in the superficial mucosa that extend into deeper layers. As inflammation advances, non-caseating granulomas form, affecting all bowel wall layers. This process creates characteristic cobblestone mucosa and skip lesions, where diseased areas alternate with healthy bowel segments, eventually leading to scar tissue formation.

The main clinical manifestations include chronic diarrhea, right lower quadrant abdominal pain that persists after defecation, and abdominal tenderness. Post-meal cramps occur due to intestinal stimulation. Chronic diarrhea can lead to weight loss, dehydration, anorexia, and nutritional deficiencies. Patients may also experience fever, oral ulcers, arthritis, and skin lesions such as erythema nodosum.

Beyond gastrointestinal symptoms, Crohn's disease can cause systemic manifestations including arthritis, skin lesions like erythema nodosum, and ocular disorders such as uveitis and episcleritis. These extraintestinal manifestations reflect the systemic nature of the inflammatory response and may occur independently of bowel symptoms, requiring comprehensive patient assessment and management.

Chronic inflammation may lead to strictures that narrow the intestinal lumen, causing abdominal pain, bloating, and obstruction. Deep ulcers can create abscesses or fistulas, and severe cases may result in intestinal perforation. Long-term inflammation, particularly in the colon, increases colorectal cancer risk. Nutritional complications such as malnutrition and anemia arise from impaired absorption and inflammation-related factors.

Although the specific cause remains unknown, predisposing factors include genetic susceptibility, environmental factors, altered gut microbiota, and a dysregulated immune response. The immune system in affected individuals reacts abnormally to gut microbiota, leading to chronic inflammation. Understanding these contributing factors helps explain disease variability and informs treatment approaches targeting immune regulation.

Crohn's disease causes transmural inflammation affecting all bowel wall layers and can involve any GI tract segment, while ulcerative colitis impacts only the colon with superficial mucosal inflammation. Crohn's disease produces skip lesions and cobblestone mucosa, whereas ulcerative colitis causes continuous inflammation. Understanding these distinctions is essential for accurate diagnosis and appropriate management of inflammatory bowel disease.