There are many people who confuse Inflammatory Bowel Disease (IBD) and Irritable Bowel Syndrome (IBS). In actuality, they are very different. IBS is a functional disorder of the intestines, in which structurally, there is no pathology. The intestines in IBD however, are inflamed or ulcerated. Ulcerative Colitis and Crohn's Disease are types of IBD. Spastic colon is another term that is used interchangeably with IBS.
The diseases are usually easily differentiated by history. At times laboratory studies, as well as imaging studies with barium (small bowel series and barium enema) is helpful. Finally, colonoscopy with biopsy can be used.
Patients with IBS typically have abdominal pain, with diarrhea and/or constipation. The pain is usually crampy in nature and relieved with a bowel movement. The pain should not awake one from sleep, and is not associated with weight loss or bleeding. When IBS patients have abdominal pain and diarrhea, the symptoms can frequently be confused with those of IBD. To make things more confusing, patients with IBS will frequently complain that their "colitis" is acting up, while in reality they never have had colitis. Patients with IBD on the other hand have important differences in their signs and symptoms. Those with Ulcerative Colitis classically present with diarrhea and rectal bleeding. Crohn's Disease is manifested by abdominal pain, diarrhea and weight loss. Bleeding may be present if there is disease in the lower part of the colon. While differentiating between IBD and IBS, one must also take into consideration colon cancer, especially in patients over the age of 50.
While usually a good history can help one differentiate the above, sometimes laboratory data can be helpful. In patients with IBS, laboratory data is normal. In IBD, patients are frequently have iron deficiency anemia; usually from blood loss. In those with Crohn's disease that involves the small bowel, malabsorption of iron can contribute as well. Erythrocyte sedimentation rate (ESR), a marker of inflammation is typically elevated in IBD as well. Stool studies in IBS will be normal, while in IBD, one frequently sees occult blood as well as the presence of white blood cells in the stool.
A final way to differentiate IBD and IBS are imaging and endoscopic studies. While colonoscopy and small bowel barium X-rays are normal in IBS, abnormalities are always present in IBD. In Ulcerative Colitis, which only involves the colon, inflammation starting in the rectum is seen at colonoscopy. The inflammation may be present throughout the colon but is always continuous. Crohn's disease involves the colon only one-third of the time, the small bowel one third of the time, and both colon and small bowel one-third of the time. When it involves the colon, inflammation will be seen at colonoscopy, but typically in a patchy distribution with areas of normal colon between abnormal areas. When Crohn's disease involves the small bowel, small bowel barium X-rays will show abnormalities, typically in the ileum. At times, biopsy may be helpful in differentiating Ulcerative Colitis from Crohn's disease.