Crohns is associated with an increased intake of animal protein, milk protein, and an increased ratio of omega-6 to omega-3 polyunsaturated fatty acids. Those who consume vegetable proteins appear to have a lower incidence of Crohns disease. Consumption of fish protein has no association.Smoking increases the risk of the return of active disease (flares). The introduction of hormonal contraception in the United States in the 1960s is associated with a dramatic increase in incidence, and one hypothesis is that these drugs work on the digestive system in ways similar to smoking. Isotretinoin is associated with Crohns.Although stress is sometimes claimed to exacerbate Crohns disease, there is no concrete evidence to support such claim. Dietary microparticles, such as those found in toothpaste, have been studied as they produce effects on immunity, but they were not consumed in greater amounts in patients with Crohns. The use of doxycycline has also been associated with increased risk of developing inflammatory bowel diseases. In one large retrospective study, patients who were prescribed doxycycline for their acne had a 2.25-fold greater risk of developing Crohns disease. Pathophysiology
During a colonoscopy, biopsies of the colon are often taken to confirm the diagnosis. Certain characteristic features of the pathology seen point toward Crohns disease; it shows a transmural pattern of inflammation, meaning the inflammation may span the entire depth of the intestinal wall. Ulceration is an outcome seen in highly active disease. There is usually an abrupt transition between unaffected tissue and the ulcer—a characteristic sign known as skip lesions.
As a result, a barium follow-through X-ray, wherein barium sulfate suspension is ingested and fluoroscopic images of the bowel are taken over time, is useful for looking for inflammation and narrowing of the small bowel. Barium enemas, in which barium is inserted into the rectum and fluoroscopy is used to image the bowel, are rarely used in the work-up of Crohns disease due to the advent of colonoscopy. They remain useful for identifying anatomical abnormalities when strictures of the colon are too small for a colonoscope to pass through, or in the detection of colonic fistulae (in this case contrast should be performed with iodate substances).CT and MRI scans are useful for evaluating the small bowel with enteroclysis protocols. They are also useful for looking for intra-abdominal complications of Crohns disease, such as abscesses, small bowel obstructions, or fistulae. Magnetic resonance imaging (MRI) is another option for imaging the small bowel as well as looking for complications, though it is more expensive and less readily available. MRI techniques such as diffusion-weighted imaging and high-resolution imaging are more sensitive in detecting ulceration and inflammation compared to CT. Blood tests
A complete blood count may reveal anemia, which commonly is caused by blood loss leading to iron deficiency or by vitamin B12 deficiency, usually caused by ileal disease impairing vitamin B12 absorption. Rarely autoimmune hemolysis may occur. Ferritin levels help assess if iron deficiency is contributing to the anemia.