Sinai Medical Ctr. But in Crohn's disease and rheumatoid arthritis, it's very over-reactive, and too much has been produced. Most commonly, the condition involves only a portion of the small intestine. But in some cases, both the small and large intestines are affected. During a flare, a patient may experience abdominal pain or cramping, diarrhea, fever, weight loss, nausea, and vomiting.
Some patients experience rectal bleeding.
In severe cases, persistent bleeding may lead to anemia. Onset usually occurs before age 35, although some cases may appear later in life. Crohn's disease is often grouped together with a similar type of gastrointestinal condition known as ulcerative colitis. Together, these two conditions are known as inflammatory bowel disease. The American Society of Colon and Rectal Surgeons estimates that two million people in the U.S. have inflammatory bowel disease.