Conditions that may be confused for IBS
Irritable bowel syndrome (IBS) is a functional bowel disorder characterized by intermittent abdominal pain or discomfort that is relieved by defecation and associated with a change in bowel habit. These symptoms are sometimes characteristic of other disorders that have an identifiable cause, a different prognosis, and require a different course of treatment than IBS. Although IBS is diagnosed based on symptoms only, and diagnostic tests may be unreliable, physicians must still rule out disorders such as infectious diarrhea, lactose intolerance, ulcerative colitis, Crohn’s disease or colorectal cancer as a cause of the symptoms.
Infectious diarrhea is characterized by crampy abdominal pain with bloody diarrhea. It is usually caused by bacteria, especially Entamoeba, Girardia, or Clostridium. People who contract infectious diarrhea usually have recently traveled to an area endemic with these bacteria. It is usually diagnosed by symptoms and the results of a stool test which will be positive for bacterial cysts and ova.
People who are lactose intolerant have abdominal discomfort, distention, and bloating following intake of diary products. They also may have diarrhea and occasional constipation. Usually lactose intolerance is diagnosed when no symptoms occur after a 2 week trial free of lactose-containing foods. A positive lactose hydrogen test confirms the diagnosis.
Ulcerative colitis is an inflammatory disease of the mucosa of the colon. It is more common in younger persons 15-35 years of age. It is usually characterized by bloody diarrhea and mucous in the stool, associated with fever, crampy abdominal pain, and weight loss. Imaging studies such as sigmoidoscopy, colonoscopy, or barium enema are used to diagnose ulcerative colitis. They will reveal irregularities such as hemorrhage, pseudopolyps, and ulceration in the mucosa.
Crohn’s Disease is an inflammatory disease that can occur anywhere along the gastrointestinal tract, from the mouth all the way to the rectum. The small intestine and the colon are the most common sites. The inflammation involves all layers of the intestinal wall. It occurs in younger persons 15-35 years old and older persons 70-80 years old. People with Crohn’s disease complain of abdominal pain, fever, diarrhea, fatigue (tiredness), and weight loss. A sigmoidoscopy, colonoscopy, or barium enema may reveal abnormalities such as ulcers, cobblestoning, and skip lesions.
Colorectal cancer, or cancer in the colon or the rectum, usually occurs in people greater than 50 years old. The symptoms usually depend on where the cancer is located in the colon. Right-sided cancers present with anemia, blood in the stool not visible to the naked eye, and weight loss. Left-sided cancers may demonstrate bleeding from the rectum, abdominal or back pain, constipation, and intermittent diarrhea.
Clarke JO, Pearson RL. Irritable Bowel Syndrome. First Consult [web page]. Aug 24 2007; www.mdconsult.com. Accessed June 20, 2008.