UC vs Crohn disease?
One of the first issues when a patient presents with symptoms suggestive of inflammatory bowel disease is to determine whether there is UC or Crohn disease (CD). There are many similarities and differences between UC and CD. There are also times when they cannot even be distinguished.
We are still learning about the underlying genetics and disease process of UC and CD, but the clinical signs, symptoms, and histopathology are well described.
Here are some of the key differences between UC and CD:
1. UC only affects the colon, while CD can involve any part of the gastrointestinal tract from the mouth to the anus. Most commonly, CD affects the terminal ileum (distal small intestine) and/or colon, less often proximal small bowel (5%), and <5% of patients have upper GI involvement (stomach/esophagus).
2. UC typically involves, and is most severe in, the rectum. There is circumferential and continuous involvement moving proximally. The severity of inflammation decreases more proximally until there is a transition to normal tissue. CD tends to spare the rectum and often has patchy involvement throughout the colon and small intestine with normal intervening mucosa.
3. The ulcers of UC are typically superficial, while those of CD, though usually superficial, are more likely to extend deeper and can even erode through the entire bowel wall.
4. Many patients with CD will develop strictures, fistulas, and abscesses in the abdomen or the anorectum. Since UC is not a transmural disease these complications are quite rare.
5. UC is strongly associated with primary sclerosing cholangitis (PSC), a disease causing strictures of the bile ducts in the liver. While only 5% of patients with UC have PSC, 50% of patients with PSC have UC. CD tends to cause kidney stones due to altered intestinal handling of oxalate.
Despite these differences, UC and CD are both autoimmune diseases, overactive immune responses against self. About 10% of the time CD can be difficult, or even impossible, to distinguish from UC, but does that even matter?