Ulcerative Colitis

Overview
  • Ulcerative Colitis (UC) is a subtype of Inflammatory Bowel Disease (IBD) and readers should refer to the IBD page for a discussion of this disease's etiopathogenesis, extra-intestinal clinical consequences, and epidemiology.
Morphology
  • Overview
    • Pathology associated with UC always begins in the rectum and spreads proximally in a continuous fashion. In nearly half of patients, disease does not extend beyond the rectum although in a handful pathology can extend throughout the entire large intestine. While inflammation can be observed in the terminal ileum in some 10% of patients, ileal pathology is not characteristic of UC itself. These features stand in contrast to Crohn Disease (CD) whose pathology is frequently discontinuous along the alimentary tract, rarely involves the rectum, yet affects the terminal ileum in nearly 90% of patients.
  • Gross Appearance
    • Active disease is characterized by easily observed and widespread ulceration of the large intestine mucosa. Small islands of regenerating mucosa bulging up from ulcerated areas are referred to as "Pseudopolyps". Although pathology associated with UC is not transmural, in rare cases ulcers can extend past the large intestine muscularis mucosa, exposing the colon's myenteric plexus, compromising colonic motility, and thus resulting in functional bowel obstruction and impaction of feces termed "Toxic Megacolon". In extreme cases intestinal mucosa can become so thinned due to ulcerations that bowel perforation results.
  • Histological Appearance
    • Inflammation in UC is exclusively limited to the large intestine mucosa]] and superficial submucosa. This stands in contrast to Crohn Disease where pathology is frequently transmural. Inflammation is characterized by a diffuse mononuclear cell infiltrate of the large intestine lamina propria. However, inflammation at the termini of large intestinal glands known as "Intestinal Crypts" is often neutrophilic, resulting in "Crypt Abscesses" similar to those seen in Crohn Disease. Ultimately, inflammatory damage of the large intestine mucosa results in severe distortion of its architecture.
Clinical Consequences
  • Clinical Course
    • UC presents with relatively long episodes of symptomology lasting weeks to months that relapse and remit over years. Episodes may be separated by years and some may be quite mild although important complications may arise from severe episodes and long-term presence of the disease.
  • Episode Symptomology:
    • The specific symptomology associated with extended episodes of UC depends on the extent and severity of pathology along the large intestine. When disease is limited to the rectum, stool is usually well-formed but bloody as it passes through the inflamed and ulcerated rectum. When pathology extends into the remainder of the large intestine, clinical diarrhea may arise likely representing excessive alimentary motility due to inflammatory irritation of the colonic mucosa (i.e. a dysmotility diarrhea). Blood in the the stool typically represents a minor source of lower GI bleeding although in rare cases bleeding can be significant. This stands in contrast to Crohn Disease where blood in the feces is infrequent.
  • Complications:
    • The most feared complication of UC is development of colorectal carcinoma whose risk increases with longer duration of disease and increased anatomic geography. Although rare, toxic megacolon and bowel perforation can occur as described above. In contrast to Crohn Disease, UC is not characterized by fibrotic strictures; in fact, development of bowel obstruction in a UC patient most likely represents development of an intestinal tumor.