Last updated: Sep 27, 2016

Brian Greenberg was only 11 when he was diagnosed with Crohn's disease. And although having a chronic inflammatory bowel disease is far from good news, he was relatively lucky in at least one aspect of the diagnosis. The first medical specialist who saw him correctly diagnosed his symptoms of stomach pain, nausea, bloody stools, exhaustion, and aching joints as Crohn's disease. Even so, Greenberg had already suffered for the better part of a year without knowing what ailed him.

As Greenberg can attest, Crohn's, a type of inflammatory bowel disease (IBD), can be notoriously difficult to pin down thanks to a set of tricky symptoms that can flare up and subside over time. It can sometimes take years to get a proper diagnosis.

"The symptoms vary from patient to patient and that's one reason that it's so hard to make a diagnosis," says Renee Young, MD, professor of internal medicine, division of gastroenterology and hepatology at the University of Nebraska Medical Center in Omaha.

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Another reason: The symptoms can mimic those of many other conditions, including ulcerative colitis (another type of IBD), appendicitis, and irritable bowel syndrome (IBS), a condition that can also cause constipation and diarrhea, but doesn't have the same inflammation or destruction of the digestive tract as an IBD.

Much of the confusion arises from the fact that Crohn's disease is an autoimmune condition that can strike unpredictably. The abnormal immune system response can damage any part of the digestive system, causing different symptoms depending on where the attack is occurring.

"It really can affect any portion of your GI tract, anywhere from the mouth to the rectum," says Alyssa Parian, MD, assistant professor of medicine at the Johns Hopkins University School of Medicine in Baltimore.

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The most frequently affected area is the connection between the small and large intestine. This can cause some of the more common, recognizable symptoms of Crohn's, such as abdominal pain (especially in the middle or right side of the abdomen), cramping, blood in the stools and changes in bowel movements.

These bowel changes are more often diarrhea, but can also be constipation, says Harold P Kaplan, MD, associate professor of medical sciences at the Frank H. Netter MD School of Medicine at Quinnipiac University in North Haven, Connecticut.

If the disease strikes higher up in the small intestine, symptoms can be mistaken for appendicitis. Crohn's that affects your mouth could result in sores or ulcers in your mouth, difficulty swallowing, and nausea and vomiting. Lower down, you may see drainage near the anus.

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Other symptoms may seem totally unrelated to the gastrointestinal tract, such as aching joints, fatigue, painful red bumps on the skin (called erythema nodosum), leg ulcers (pyoderma gangrenosum), and sore, red eyes. That's because the immune system may not only affect the digestive tract, but other parts of the body too.

And some people just feel bad in a vague way.

"People with Crohn's disease, once it gets established, generally are constitutionally ill," says Dr. Kaplan. "Their appetite is off, they tend to lose weight." Children (Greenberg was one) are particularly vulnerable to losing weight and falling off the growth curve.

There may also be fever, night sweats and anemia or vitamin B12 deficiency if your body is not absorbing enough nutrients.

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Whatever they are, symptoms of Crohn's can be severe—like Greenberg's were—or mild. And there can be a lot of variation within any time frame.

"It really can be a giant roller coaster," says Greenberg, now 33 and a financial professional in Stamford, Connecticut, as well as founder of the site "I have nights where I feel fine and my girlfriend is cooking dinner, then right before dinner, the nausea hits me and I want to throw up."

"It's not unusual for there to be a few days or weeks when you feel uncomfortable with pain in your bowels then, without any particular treatment, hit a stretch when you feel just fine," says Dr. Kaplan.

Whatever the symptoms may be, they are just one element that can help diagnose Crohn's. If you think you might have Crohn's see your doctor, who can perform tests, including a full colonoscopy, to diagnose the condition.