Several conditions cause symptoms nearly identical to Crohn’s disease, including chronic diarrhea, abdominal pain, weight loss, and fatigue. Some involve genuine intestinal inflammation, while others mimic Crohn’s without causing any structural damage to the gut. Telling them apart matters because the treatments are very different.
Ulcerative Colitis
Ulcerative colitis is the condition most commonly confused with Crohn’s. Both fall under inflammatory bowel disease (IBD), and they share many symptoms: bloody diarrhea, cramping, urgency, and flares that come and go. The key differences are location and depth. Ulcerative colitis only affects the large intestine, starting at the rectum and spreading upward in one continuous stretch with no gaps. Crohn’s can strike anywhere from the mouth to the anus, and it typically skips around, leaving patches of healthy tissue between inflamed areas.
The inflammation itself behaves differently too. In ulcerative colitis, only the innermost lining of the colon is inflamed. In Crohn’s, inflammation can penetrate through the entire thickness of the intestinal wall, which is why Crohn’s is more likely to cause fistulas (abnormal tunnels between organs) and strictures (narrowed segments of bowel).
In roughly 5 to 6% of IBD cases, doctors can’t confidently call it one or the other, a situation termed indeterminate colitis. In children, that rate climbs as high as 23%. Over time, most of these cases are eventually reclassified. In one well-known series, about 40% of initially indeterminate cases turned out to be Crohn’s, and another quarter were reclassified as ulcerative colitis. Blood tests for specific antibodies can help: one combination of markers predicts Crohn’s in about 80% of cases, while the opposite pattern points toward ulcerative colitis.
Irritable Bowel Syndrome
Irritable bowel syndrome (IBS) is probably the most common condition mistaken for early Crohn’s. The overlap in symptoms is real: cramping, bloating, diarrhea, and constipation. But IBS is a functional disorder, meaning the gut isn’t structurally damaged. There are no ulcers, no inflammation visible on a scope, and no bowel wall thickening on imaging.
The most reliable way to separate the two is a stool test that measures a protein called calprotectin. In IBS, calprotectin levels are normal. In active IBD, they’re elevated. At a cutoff of 50 micrograms per gram, the test catches 100% of IBD cases, with about 60% specificity. One analysis found that if a person with IBS-like symptoms has both a normal calprotectin and a normal blood inflammation marker, the chance they actually have IBD is 1% or less. This simple, noninvasive test can spare many people from unnecessary colonoscopies.
Celiac Disease
Celiac disease shares several hallmark symptoms with Crohn’s: diarrhea, bloating, abdominal pain, weight loss, and poor nutrient absorption. Both conditions can cause anemia, fatigue, and even joint pain. The difference is the cause. Celiac disease is an immune reaction to gluten, a protein in wheat, barley, and rye, while Crohn’s inflammation isn’t triggered by any single dietary protein.
Celiac disease primarily damages the upper small intestine, whereas Crohn’s most often affects the lower end of the small intestine and the colon. A blood test screening for specific antibodies to gluten can quickly flag celiac disease, and a biopsy of the upper small intestine confirms it. Because the two conditions occasionally coexist, doctors often test for celiac when evaluating someone for possible Crohn’s.
Infections That Look Like Crohn’s
Certain gut infections create inflammation in the exact same part of the intestine Crohn’s favors, the terminal ileum, and can even produce identical findings on biopsy. The most notable culprit is a bacterium called Yersinia. Yersinia infection causes ulcers in the terminal ileum, swollen lymph nodes in the abdomen, and granulomas (tiny clusters of immune cells) in tissue samples. All of these are classic Crohn’s findings.
Yersinia can also trigger complications outside the gut that overlap with Crohn’s, including joint inflammation and a painful skin condition called erythema nodosum. In some cases, the infection mimics appendicitis so convincingly that patients undergo emergency surgery only to find a normal appendix and an inflamed ileum. Because doctors don’t routinely test for Yersinia antibodies, some of these infections are misdiagnosed as new-onset Crohn’s. Adding to the complexity, Yersinia infection and Crohn’s can occur together in the same patient.
Microscopic Colitis
Microscopic colitis causes chronic watery diarrhea that can persist for months, along with cramping and fatigue. What makes it tricky is that the colon looks completely normal during a colonoscopy. The inflammation only shows up under a microscope when tissue samples are examined, hence the name. In Crohn’s or ulcerative colitis, by contrast, visible ulcers, redness, and swelling are usually apparent during the procedure.
Microscopic colitis tends to affect older adults, particularly women, and is strongly associated with certain medications. It doesn’t cause the deep ulcers, fistulas, or bowel wall thickening seen in Crohn’s, and it generally responds well to a single anti-inflammatory medication.
NSAID-Induced Gut Injury
Regular use of common pain relievers like ibuprofen and naproxen can damage the lining of the small intestine in ways that look remarkably like Crohn’s disease. On imaging and endoscopy, NSAID-related injury in the terminal ileum can show redness, erosions, and ulcers. In more severe cases, it can even cause strictures.
The pattern can be difficult to distinguish from mild Crohn’s, especially if a patient doesn’t mention their NSAID use or considers it too routine to report. The difference usually becomes clear when stopping the medication leads to healing, something that wouldn’t happen with true Crohn’s.
Behcet’s Disease
Behcet’s disease is a systemic condition that causes inflammation in blood vessels throughout the body. When it involves the intestines, it typically produces ulcers in the same ileocecal area where Crohn’s concentrates. The endoscopic findings can include deep, punched-out ulcers, fistulas, and even the cobblestone appearance of the intestinal lining considered a hallmark of Crohn’s.
In rare presentations, Behcet’s causes skip lesions with rectal sparing, longitudinal ulcers, and inflammation through the full thickness of the bowel wall, all features that would strongly suggest Crohn’s on their own. The distinguishing clues come from outside the gut: Behcet’s classically causes recurrent mouth ulcers, genital ulcers, eye inflammation, and skin lesions. When intestinal symptoms appear alongside these features, Behcet’s moves to the top of the list.
Diverticulitis
Diverticulitis, an infection or inflammation of small pouches that form in the colon wall, can cause abdominal pain, fever, and changes in bowel habits that overlap with a Crohn’s flare. Both conditions tend to cause left-sided or lower abdominal pain, and both can lead to abscesses or fistulas in severe cases.
Diverticulitis is most common in people over 50, though it increasingly affects younger adults. On a CT scan, it typically shows localized thickening of the colon wall with surrounding fat inflammation, centered around visible pouches. Crohn’s, by contrast, tends to show longer segments of bowel involvement, cobblestoning of the inner lining, and aphthous ulcers on endoscopy. Granulomas on biopsy and perianal disease are reliable markers that point toward Crohn’s rather than diverticulitis.