Crohns is responsible for 10% of vesicoenteric fistulae, and is the most common cause of ileovesical fistulae.Symptoms caused by intestinal stenosis, or the tightening and narrowing of the bowel, are also common in Crohns disease. Abdominal pain is often most severe in areas of the bowel with stenosis. Persistent vomiting and nausea may indicate stenosis from small bowel obstruction or disease involving the stomach, pylorus, or duodenum.Intestinal granulomas are a walled-off portions of the intestine by macrophages in order to isolate infections. Granuloma formation is more often seen in younger patients, and mainly in the severe, active penetrating disease. Granuloma is considered the hallmark of microscopic diagnosis in Crohns disease (CD), but granulomas can be detected in only 21-60% of CD patients. Cancer
Crohns disease also increases the risk of cancer in the area of inflammation. For example, individuals with Crohns disease involving the small bowel are at higher risk for small intestinal cancer. Similarly, people with Crohns colitis have a relative risk of 5.6 for developing colon cancer. Screening for colon cancer with colonoscopy is recommended for anyone who has had Crohns colitis for at least eight years.Some studies suggest there is a role for chemoprotection in the prevention of colorectal cancer in Crohns involving the colon; two agents have been suggested, folate and mesalamine preparations. Also, immunomodulators and biologic agents used to treat this disease may promote developing extra-intestinal cancers.Some cancers, such as Acute Myelocytic Leukaemia have been described in cases of Crohns disease.
Another study theorized that the human immune system traditionally evolved with the presence of parasites inside the body and that the lack thereof due to modern hygiene standards has weakened the immune system. Test subjects were reintroduced to harmless parasites, with positive responses. Microbes
It is hypothesized that maintenance of commensal microorganism growth in the GI tract is dysregulated, either as a result or cause of immune dysregulation.There is an apparent connection between Crohns disease, Mycobacterium, other pathogenic bacteria, and genetic markers. A number of studies have suggested a causal role for Mycobacterium avium subspecies paratuberculosis (MAP), which causes a similar disease, Johnes disease, in cattle. In many individuals, genetic factors predispose individuals to Mycobacterium avium subsp. paratuberculosis infection. This bacterium may produce certain compounds containing mannose, which may protect both itself and various other bacteria from phagocytosis, thereby possibly causing a variety of secondary infections.NOD2 is a gene involved in Crohns genetic susceptibility. It is associated with macrophages diminished ability to phagocytize MAP. This same gene may reduce innate and adaptive immunity in gastrointestinal tissue and impair the ability to resist infection by the MAP bacterium. Macrophages that ingest the MAP bacterium are associated with high production of TNF-α.Other studies have linked specific strains of enteroadherent E. coli to the disease.