Some people interchange Crohn's disease and ulcerative colitis (UC) because there are certain similarities between these two ailments. They are two different types of inflammatory bowel disease (IBD)1 — the umbrella term for these conditions (Other lesser-known types of IBD include collagenous colitis and lymphocytic colitis.)
Crohn's disease and ulcerative colitis both occur in teenagers and young adults. They affect women and men equally, and their symptoms are very similar. What's more, their definitive causes have not yet been determined, although genes, environmental exposure, and poor immune response are both seen as contributing factors to both of these diseases.
However, what sets these two apart is the area (or areas) they affect. While they both cause chronic inflammation in the gastrointestinal (GI) tract, ulcerative colitis is limited to the rectum and colon, or the large intestine. It begins in the rectum or sigmoid colon, and spreads up through the colon as the disease progresses. The inflammation and irritation mostly affect only the innermost layer of the intestine lining.2 On the other hand, Crohn's disease can manifest generally on any area throughout the GI, from the mouth to the anus. It may also appear in patches. Some areas may be affected, while some sections can be inflammation-free.3
However, it occurs in all the layers of the bowel walls (unlike UC, which only affects the innermost layer). As a result of the deep ulcers and tissue swelling, the bowel walls affected by Crohn's disease become thicker, with a cobblestoned appearance. In ulcerative colitis, the bowel walls remain thin, but lose their vascular pattern (meaning the blood vessels are not visible), and there are no patches of healthy tissue that can be seen in the affected areas.
Another telltale sign of Crohn's disease is the presence of granulomas, which are inflamed cells that are lumped together to form a lesion. Since granulomas are present in Crohn's disease, but not in ulcerative colitis colitis, the presence of these can help your physician reach a definite diagnosis.
Crohn's disease may also lead to complications like strictures, fistulas, and fissures, which are less frequent in UC cases. Both Crohn's disease and UC are chronic conditions, meaning they may have periods of being symptom-free (remission), but with occasional flare-ups. Their symptoms are generally the same: cramping, persistent diarrhea, and abdominal pain.4
However, Crohn's disease patients usually feel the pain in their lower right abdomen, while UC patients experience it in the lower left abdomen. Most UC patients also have some bloody discharge with their stool, while this occurs much less commonly in people with Crohn's disease.