Inflammatory Bowel Disease IV: Clinical Manifestations

Ulcerative colitis affects only the colon and rectum with mucosal inflammation, while Crohn's disease involves transmural inflammation extending through the entire bowel wall and can affect any part of the gastrointestinal tract. Ulcerative colitis follows a pattern of flares and remission, whereas Crohn's disease often affects the small intestine, particularly the terminal ileum, causing vitamin B12 deficiency and bile acid malabsorption.

Mild ulcerative colitis flares present with slight increases in bowel movements, mild abdominal cramping, and small amounts of rectal bleeding due to superficial mucosal injury. These symptoms reflect limited inflammation of the mucosal layer and are typically less severe than extensive flares.

Severe ulcerative colitis causes diffuse abdominal pain, fever, and tachycardia, with patients passing six or more bloody stools daily. Persistent blood and fluid losses lead to dehydration, iron-deficiency anemia, weight loss, and profound fatigue. Extensive inflammation also impairs nutrient absorption and protein balance, contributing to systemic complications.

Crohn's disease frequently affects the terminal ileum, the primary site of vitamin B12 and bile acid absorption. Transmural inflammation in this region impairs nutrient absorption, leading to vitamin B12 deficiency and subsequent malabsorption complications including steatorrhea, weight loss, and anemia.

Transmural inflammation in Crohn's disease extends through the full thickness of the bowel wall, predisposing patients to strictures, fistulas, and abscesses. These complications contribute to chronic abdominal pain and weight loss, distinguishing Crohn's disease from ulcerative colitis and requiring different management approaches.

Diarrhea is a hallmark symptom of Crohn's disease and may be accompanied by rectal bleeding when the colon is involved. In ulcerative colitis, diarrhea manifests as increased stool frequency during flares. Crohn's diarrhea often reflects small intestine involvement and malabsorption, whereas ulcerative colitis diarrhea results from mucosal inflammation limited to the colon and rectum.

Chronic blood loss in inflammatory bowel disease, particularly during severe ulcerative colitis flares, causes iron-deficiency anemia, dehydration, weight loss, and fatigue. These systemic effects reflect ongoing mucosal damage and fluid losses, requiring management to restore iron stores and maintain nutritional status.