Crohn's disease

Crohn's disease, also known as regional enteritis, is an inflammatory disease of the intestines that may affect any part of the gastrointestinal tract from mouth to anus, causing a wide variety of symptoms. It primarily causes abdominal pain, diarrhea (which may be bloody if inflammation is at its worst), vomiting (can be continuous), or weight loss, but may also cause complications outside the gastrointestinal tract such as skin rashes, arthritis, inflammation of the eye, tiredness, and lack of concentration.

Crohn's disease is thought to be an autoimmune disease, in which the body's immune system attacks the gastrointestinal tract, causing inflammation; it is classified as a type of inflammatory bowel disease. There is evidence of a genetic link to Crohn's disease, putting individuals with siblings afflicted with the disease at higher risk. Males and females are equally affected. Smokers are two times more likely to develop Crohn's disease than nonsmokers. Crohn's disease affects between 400,000 and 600,000 people in North America. Prevalence estimates for Northern Europe have ranged from 27–48 per 100,000. Crohn's disease tends to present initially in the teens and twenties, with another peak incidence in the fifties to seventies, although the disease can occur at any age. There is no known pharmaceutical or surgical cure for Crohn's disease. Treatment options are restricted to controlling symptoms, maintaining remission, and preventing relapse.

The disease was named after American gastroenterologist Burrill Bernard Crohn, who, in 1932, together with two colleagues, described a series of patients with inflammation of the terminal ileum, the area most commonly affected by the illness. For this reason, the disease has also been called regional ileitis or regional enteritis. The condition, however, had previously been independently described in medical literature by others. The most notable case was in 1904 by Polish surgeon Antoni Leśniowski for whom the condition is alternatively named Leśniowski-Crohn's disease in Polish literature.

Classification
Crohn's disease is one type of inflammatory bowel disease (IBD). It typically manifests in the gastrointestinal tract and can be categorized by the specific tract region affected. A disease of both the ileum (the last part of the small intestine, which connects to the large intestine), and the large intestine, Ileocolic Crohn's accounts for fifty percent of cases. Crohn's ileitis, manifest in the ileum only, accounts for thirty percent of cases, while Crohn's colitis, of the large intestine, accounts for the remaining twenty percent of cases and may be particularly difficult to distinguish from ulcerative colitis. Gastroduodenal Crohn's disease causes inflammation in the stomach and first part of the small intestine, called the duodenum. Jejunoileitis causes spotty patches of inflammation in the top half of the small intestine, called the jejunum (MedlinePlus 2010). The disease can attack any part of the digestive tract, from mouth to anus. However, individuals affected by the disease rarely fall outside these three classifications, with presentations in other areas.

Crohn's disease may also be categorized by the behavior of disease as it progresses. These categorizations formalized in the Vienna classification of the disease. There are three categories of disease presentation in Crohn's disease: stricturing, penetrating, and inflammatory. Stricturing disease causes narrowing of the bowel that may lead to bowel obstruction or changes in the caliber of the feces. Penetrating disease creates abnormal passageways (fistulae) between the bowel and other structures, such as the skin. Inflammatory disease (or nonstricturing, nonpenetrating disease) causes inflammation without causing strictures or fistulae.

Gastrointestinal
Many people with Crohn's disease have symptoms for years prior to the diagnosis. The usual onset is between 15 and 30 years of age, but can occur at any age. Because of the 'patchy' nature of the gastrointestinal disease and the depth of tissue involvement, initial symptoms can be more subtle than those of ulcerative colitis. People with Crohn's disease experience chronic recurring periods of flare-ups and remission.

Abdominal pain may be the initial symptom of Crohn's disease. It is often accompanied by diarrhea, especially in those who have had surgery. The diarrhea may or may not be bloody. People who have had surgery or multiple surgeries often end up with short bowel syndrome of the gastrointestinal tract. The nature of the diarrhea in Crohn's disease depends on the part of the small intestine or colon involved. Ileitis typically results in large-volume, watery feces. Colitis may result in a smaller volume of feces of higher frequency. Fecal consistency may range from solid to watery. In severe cases, an individual may have more than 20 bowel movements per day and may need to awaken at night to defecate. Visible bleeding in the feces is less common in Crohn's disease than in ulcerative colitis, but may be seen in the setting of Crohn's colitis. Bloody bowel movements are typically intermittent, and may be bright or dark red in color. In the setting of severe Crohn's colitis, bleeding may be copious. Flatulence and bloating may also add to the intestinal discomfort.

Symptoms caused by intestinal stenosis are also common in Crohn's disease. Abdominal pain is often most severe in areas of the bowel with stenoses. In the setting of severe stenosis, vomiting and nausea may indicate the beginnings of small bowel obstruction. Although the association is greater in the context of ulcerative colitis, Crohn's disease may also be associated with primary sclerosing cholangitis, a type of inflammation of the bile ducts.

Perianal discomfort may also be prominent in Crohn's disease. Itchiness or pain around the anus may be suggestive of inflammation, fistulization or abscess around the anal area or anal fissure. Perianal skin tags are also common in Crohn's disease. Fecal incontinence may accompany perianal Crohn's disease. At the opposite end of the gastrointestinal tract, the mouth may be affected by non-healing sores (aphthous ulcers). Rarely, the esophagus, and stomach may be involved in Crohn's disease. These can cause symptoms including difficulty swallowing (dysphagia), upper abdominal pain, and vomiting.

Systemic
Crohn's disease, like many other chronic, inflammatory diseases, can cause a variety of systemic symptoms. Among children, growth failure is common. Many children are first diagnosed with Crohn's disease based on inability to maintain growth. As it may manifest at the time of the growth spurt in puberty, up to 30% of children with Crohn's disease may have retardation of growth. Fever may also be present, though fevers greater than 38.5 ˚C (101.3 ˚F) are uncommon unless there is a complication such as an abscess. Among older individuals, Crohn's disease may manifest as weight loss, usually related to decreased food intake, since individuals with intestinal symptoms from Crohn's disease often feel better when they do not eat and might lose their appetite. People with extensive small intestine disease may also have malabsorption of carbohydrates or lipids, which can further exacerbate weight loss.

Extraintestinal


In addition to systemic and gastrointestinal involvement, Crohn's disease can affect many other organ systems. Inflammation of the interior portion of the eye, known as uveitis, can cause eye pain, especially when exposed to light (photophobia). Inflammation may also involve the white part of the eye (sclera), a condition called episcleritis. Both episcleritis and uveitis can lead to loss of vision if untreated.

Crohn's disease is associated with a type of rheumatologic disease known as seronegative spondyloarthropathy. This group of diseases is characterized by inflammation of one or more joints (arthritis) or muscle insertions (enthesitis). The arthritis can affect larger joints, such as the knee or shoulder, or may exclusively involve the small joints of the hands and feet. The arthritis may also involve the spine, leading to ankylosing spondylitis if the entire spine is involved or simply sacroiliitis if only the lower spine is involved. The symptoms of arthritis include painful, warm, swollen, stiff joints and loss of joint mobility or function.

Crohn's disease may also involve the skin, blood, and endocrine system. One type of skin manifestation, erythema nodosum, presents as red nodules usually appearing on the shins. Erythema nodosum is due to inflammation of the underlying subcutaneous tissue, and is characterized by septal panniculitis. Another skin lesion, pyoderma gangrenosum, is typically a painful ulcerating nodule. Crohn's disease also increases the risk of blood clots; painful swelling of the lower legs can be a sign of deep venous thrombosis, while difficulty breathing may be a result of pulmonary embolism. Autoimmune hemolytic anemia, a condition in which the immune system attacks the red blood cells, is also more common in Crohn's disease and may cause fatigue, pallor, and other symptoms common in anemia. Clubbing, a deformity of the ends of the fingers, may also be a result of Crohn's disease. Finally, Crohn's disease may cause osteoporosis, or thinning of the bones. Individuals with osteoporosis are at increased risk of bone fractures.

Crohn's disease can also cause neurological complications (reportedly in up to 15% of patients). The most common of these are seizures, stroke, myopathy, peripheral neuropathy, headache and depression.

Crohn's patients often also have issues with small bowel bacterial overgrowth syndrome, which has similar symptoms.

In the oral cavity crohn's patients may suffer from cheilitis granulomatosa and other forms of orofacial granulomatosis, pyostomatitis vegetans, recurrent aphthous stomatitis, geographic tongue and migratory stomatitis in higher prevalence than the general population.

Complications
Crohn's disease can lead to several mechanical complications within the intestines, including obstruction, fistulae, and abscesses. Obstruction typically occurs from strictures or adhesions that narrow the lumen, blocking the passage of the intestinal contents. Fistulae can develop between two loops of bowel, between the bowel and bladder, between the bowel and vagina, and between the bowel and skin. Abscesses are walled off collections of infection, which can occur in the abdomen or in the perianal area in Crohn's disease sufferers. Crohn's is responsible for 10% of vesicoenteric fistulae, and is the most common cause of ileovesical fistulae.

Crohn's disease also increases the risk of cancer in the area of inflammation. For example, individuals with Crohn's disease involving the small bowel are at higher risk for small intestinal cancer. Similarly, people with Crohn's 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 Crohn's colitis for at least eight years. Some studies suggest there is a role for chemoprotection in the prevention of colorectal cancer in Crohn's involving the colon; two agents have been suggested, folate and mesalamine preparations.

Individuals with Crohn's disease are at risk of malnutrition for many reasons, including decreased food intake and malabsorption. The risk increases following resection of the small bowel. Such individuals may require oral supplements to increase their caloric intake, or in severe cases, total parenteral nutrition (TPN). Most people with moderate or severe Crohn's disease are referred to a dietitian for assistance in nutrition.

Crohn's disease can cause significant complications, including bowel obstruction, abscesses, free perforation and hemorrhage.

Crohn's disease can be problematic during pregnancy, and some medications can cause adverse outcomes for the fetus or mother. Consultation with an obstetrician and gastroenterologist about Crohn's disease and all medications allows preventative measures to be taken. In some cases, remission can occur during pregnancy. Certain medications can also impact sperm count or may otherwise adversely affect a man's ability to conceive.

Cause
Although the exact cause of Crohn's disease is still unknown, a combination of environmental factors and genetic predisposition seems to cause the disease. The genetic risk factors have now more or less been comprehensively elucidated, making Crohn's disease the first genetically complex disease of which the genetic background has been resolved. The relative risks of contracting the disease when one has a mutation in one of the risk genes, however, are actually very low (approximately 1:200). In broad terms, the genetic data indicate the innate immune systems in patients with Crohn's disease malfunction, and direct assessment of patient immunity confirms this notion. This had led to the notion Crohn's disease should be viewed as innate immune deficiency, chronic inflammation being caused by adaptive immunity trying to compensate for the reduced function of the innate immune system.

Genetics
Some research has indicated Crohn's disease may have a genetic link. The disease runs in families and those with a sibling with the disease are 30 times more likely to develop it than the general population.

Mutations in the CARD15 gene (also known as the NOD2 gene) are associated with Crohn's disease and with susceptibility to certain phenotypes of disease location and activity. In earlier studies, only two genes were linked to Crohn's, but scientists now believe over thirty genes show genetics play a role in the disease, either directly through causation or indirectly, as with a mediator variable. Anomalies in the XBP1 gene have recently been identified as a factor, pointing towards a role for the unfolded protein response pathway of the endoplasmatic reticulum in inflammatory bowel diseases.

Environmental factors
Diet is believed to be linked to its higher prevalence in industrialized parts of the world. A positive correlation has been found between the incidence of the disease and an increased intake of animal protein, milk protein and an increased ratio of omega-6 to omega-3 polyunsaturated fatty acids. Negative correlation of the disease incidence was found in the increased consumption of vegetable protein, and no correlation to fish protein. Smoking has been shown to increase the risk of the return of active disease, or "flares". The introduction of hormonal contraception in the United States in the 1960s is linked with a dramatic increase in the incidence rate of Crohn's disease. Although a causal linkage has not been effectively shown, there remain fears these drugs work on the digestive system in ways similar to smoking. Several scientific studies have posited isotretinoin is a possible cause of Crohn's disease in some individuals. Emotional stress is also likely contribute to the progression and worsening of Crohn's disease.

Immune system
Abnormalities in the immune system have often been invoked as being causes of Crohn's disease. It is thought to be an autoimmune disease, with inflammation stimulated by an overactive Th1 cytokine response. However, more recent evidence has shown Th17 is of greater importance in the disease. The most recent gene to be implicated in Crohn's disease is ATG16L1, which may induce autophagy and hinder the body's ability to attack invasive bacteria.

Contrary to the prevailing view that Crohn's disease is a primary T cell autoimmune disorder, there is an increasing body of evidence in favor of the hypothesis that Crohn's disease results from an impaired innate immunity. The immunodeficiency, which has been shown to be due (at least in part) to impaired cytokine secretion by macrophages, is thought to lead to a sustained microbial-induced inflammatory response, in particular, in the colon where the bacterial load is especially high.

Microbes
A variety of pathogenic bacteria were initially suspected of being causative agents of Crohn's disease. However, most healthcare professionals now believe a variety of microorganisms are taking advantage of their host's weakened mucosal layer and inability to clear bacteria from the intestinal walls, both symptoms of the disease. Some studies have suggested Mycobacterium avium subspecies paratuberculosis (MAP) plays a role in Crohn's disease, in part because it causes a very similar disease, Johne's disease, in cattle. The mannose-bearing antigens (mannins) from yeast may also elicit an antibody response. Other studies have linked specific strains of enteroadherent E. coli to the disease. Still, this relationship between specific types of bacteria and Crohn's disease remains unclear.

Some studies have suggested some symptoms of Crohn's disease, ulcerative colitis and irritable bowel syndrome have the same underlying cause. Biopsy samples taken from the colons of all three patient groups were found to produce elevated levels of a serine protease. Experimental introduction of the serine protease into mice has been found to produce widespread pain associated with irritable bowel syndrome, as well as colitis, which is associated with all three diseases. The authors of that study were unable to identify the source of the protease, but a separate review noted regional and temporal variations in those illnesses follow those associated with infection with a poorly understood protozoan, Blastocystis.

A study in 2003 put forth the "cold-chain" hypothesis that psychrotrophic bacteria such as Yersinia and Listeria species contribute to the disease. A statistical correlation was found between the advent of the use of refrigeration in the United States and various parts of Europe and the rise of the disease. Later studies have provided support for this hypothesis.

Studies done at the University of Liverpool have offered ideas to explain the apparent connection between Crohn's disease, Mycobacterium, other pathogenic bacteria, and genetic markers. In many individuals, genetic factors predispose individuals to Mycobacterium avium subsp. paratuberculosis infection. This bacterium then produces mannins, which protect both itself and various bacteria from phagocytosis, which causes a variety of secondary infections.

Pathophysiology
During a colonoscopy, biopsies of the colon are often taken to confirm the diagnosis. Certain characteristic features of the pathology seen point toward Crohn's 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. Under a microscope, biopsies of the affected colon may show mucosal inflammation, characterized by focal infiltration of neutrophils, a type of inflammatory cell, into the epithelium. This typically occurs in the area overlying lymphoid aggregates. These neutrophils, along with mononuclear cells, may infiltrate the crypts, leading to inflammation (crypititis) or abscess (crypt abscess). Granulomas, aggregates of macrophage derivatives known as giant cells, are found in 50% of cases and are most specific for Crohn's disease. The granulomas of Crohn's disease do not show "caseation", a cheese-like appearance on microscopic examination characteristic of granulomas associated with infections, such as tuberculosis. Biopsies may also show chronic mucosal damage, as evidenced by blunting of the intestinal villi, atypical branching of the crypts, and a change in the tissue type (metaplasia). One example of such metaplasia, Paneth cell metaplasia, involves development of Paneth cells (typically found in the small intestine) in other parts of the gastrointestinal system.

Diagnosis


The diagnosis of Crohn's disease can sometimes be challenging, and a number of tests are often required to assist the physician in making the diagnosis. Even with a full battery of tests, it may not be possible to diagnose Crohn's with complete certainty; a colonoscopy is approximately 70% effective in diagnosing the disease, with further tests being less effective. Disease in the small bowel is particularly difficult to diagnose, as a traditional colonoscopy allows access to only the colon and lower portions of the small intestines; introduction of the capsule endoscopy aids in endoscopic diagnosis. Multinucleated giant cells, a common finding in the lesions of Crohn's disease, are less common in the lesions of lichen nitidus.

Endoscopy
A colonoscopy is the best test for making the diagnosis of Crohn's disease, as it allows direct visualization of the colon and the terminal ileum, identifying the pattern of disease involvement. On occasion, the colonoscope can travel past the terminal ileum, but it varies from patient to patient. During the procedure, the gastroenterologist can also perform a biopsy, taking small samples of tissue for laboratory analysis, which may help confirm a diagnosis. As 30% of Crohn's disease involves only the ileum, cannulation of the terminal ileum is required in making the diagnosis. Finding a patchy distribution of disease, with involvement of the colon or ileum, but not the rectum, is suggestive of Crohn's disease, as are other endoscopic stigmata. The utility of capsule endoscopy for this, however, is still uncertain. A "cobblestone"-like appearance is seen in approximately 40% of cases of Crohn's disease upon colonoscopy, representing areas of ulceration separated by narrow areas of healthy tissue.

Radiologic tests
A small bowel follow-through may suggest the diagnosis of Crohn's disease and is useful when the disease involves only the small intestine. Because colonoscopy and gastroscopy allow direct visualization of only the terminal ileum and beginning of the duodenum, they cannot be used to evaluate the remainder of the small intestine. 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 Crohn's 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 Crohn's 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

Nuclear scans
Multiphase white blood cell scans have been shown to be effective in detecting the locations of active Crohn's disease, particularly in hard to diagnose patients suffering with the early stages or a mild form of the disease with negative endoscopic and radiologic findings. The procedure, a type of nuclear medicine, uses white blood cells removed from the patient; they are tagged with a radioisotope, and then injected intravenously into the patient, and later scanned at several intervals to detect any abnormal white blood cell accumulation, such as pooling in the intestinal tract. Studies have also suggested such scans are useful to monitor the disease and evaluate the effectiveness of therapy.

Blood tests
A complete blood count may reveal anemia, which may be caused by blood loss, by vitamin B deficiency or, possibly, autoimmune hemolysis. The latter may be seen with ileitis because vitamin B is absorbed in the ileum. Erythrocyte sedimentation rate, or ESR, and C-reactive protein measurements can also be useful to gauge the degree of inflammation. It is also true in patients with an ilectomy done in response to the complication. Another cause of anemia is anemia of chronic disease, characterized by its microcytic and hypochromic anemia. There can be various reasons for it, including medication used in treatment of inflammatory bowel disease, like azathioprine, which can lead to cytopenia, and sulfasalazine, which can also result in folate malabsorption, etc. Testing for Saccharomyces cerevisiae antibodies (ASCA) and antineutrophil cytoplasmic antibodies (ANCA) has been evaluated to identify inflammatory diseases of the intestine and to differentiate Crohn's disease from ulcerative colitis. Furthermore, increasing amounts and levels of serological antibodies such as ASCA, antilaminaribioside [Glc(β1,3)Glb(β); ALCA], antichitobioside (GlcNAc(β1,4)GlcNAc(β); ACCA], antimannobioside [Man(α1,3)Man(α)AMCA], antiLaminarin [Glc(β1,3))3n(Glc(β1,6))n; anti-L] and antichitin [(GlcNAc(β1,4)n; anti-C] associate with disease behavior and surgery, and may aid in the prognosis of Crohn's disease.

Comparison with ulcerative colitis
The most common disease that mimics the symptoms of Crohn's disease is ulcerative colitis, as both are inflammatory bowel diseases that can affect the colon with similar symptoms. It is important to differentiate these diseases, since the course of the diseases and treatments may be different. In some cases, however, it may not be possible to tell the difference, in which case the disease is classified as indeterminate colitis.

Management
At the present time, there is no cure for Crohn's disease and remission may not be possible or prolonged if achieved. In cases where remission is possible, relapse can be prevented and symptoms controlled with medication, lifestyle changes, and, in some cases, surgery. Adequately controlled, Crohn's disease may not significantly restrict daily living. Treatment for Crohn's disease is only when symptoms are active and involve first treating the acute problem, then maintaining remission.

Lifestyle changes
Certain lifestyle changes can reduce symptoms, including dietary adjustments Elemental diet, proper hydration, and smoking cessation. Smoking may increase Crohn's disease; stopping is recommended. Eating small meals frequently instead of big meals may also help with a low appetite. To manage symptoms have a balanced diet with proper portion control. Fatigue can be helped with regular exercise, a healthy diet, and enough sleep. A food diary may help with identifying foods that trigger symptoms. Some patients should follow a low dietary fiber diet to control symptoms especially if fibrous foods cause symptoms. Patients should avoid milk or dairy products as they have been shown in recent research (2007) to contribute to or even cause Crohn's disease.

Medication
Acute treatment uses medications to treat any infection (normally antibiotics) and to reduce inflammation (normally aminosalicylate anti-inflammatory drugs and corticosteroids). When symptoms are in remission, treatment enters maintenance, with a goal of avoiding the recurrence of symptoms. Prolonged use of corticosteroids has significant side-effects; as a result, they are, in general, not used for long-term treatment. Alternatives include aminosalicylates alone, though only a minority are able to maintain the treatment, and many require immunosuppressive drugs. It has been also suggested that antibiotics change the enteric flora, and their continuous use may pose the risk of overgrowth with pathogens such as Clostridium difficile.

Medications used to treat the symptoms of Crohn's disease include 5-aminosalicylic acid (5-ASA) formulations, prednisone, immunomodulators such as azathioprine, mercaptopurine, methotrexate, infliximab, adalimumab, certolizumab and natalizumab. Hydrocortisone should be used in severe attacks of Crohn's disease.

Surgery
Crohn's cannot be cured by surgery, though it is used when partial or a full blockage of the intestine occurs. Surgery may also be required for complications such as obstructions, fistulas and/or abscesses, or if the disease does not respond to drugs. After the first surgery, Crohn's usually shows up at the site of the resection, however it can appear in other locations. After a resection, scar tissue builds up, which can cause strictures, which form when the intestines become too small to allow excrement to pass through easily, which can lead to a blockage. After the first resection, another resection may be necessary within five years. For patients with an obstruction due to a stricture, two options for treatment are strictureplasty and resection of that portion of bowel. There is no statistical significance between strictureplasty alone versus strictureplasty and resection in cases of duodenal involvement. In these cases, re-operation rates were 31% and 27%, respectively, indicating that strictureplasty is a safe and effective treatment for selected patients with duodenal involvement.

Short bowel syndrome (SBS, also short gut syndrome or simply short gut) can be caused by the surgical removal of the small intestines. It usually develops in those having had half or more of their small intestines removed. Diarrhea is the main symptom of short bowel syndrome, however other symptoms may include cramping, bloating, and heartburn. Short bowel syndrome is treated with changes in diet, intravenous feeding, vitamin and mineral supplements, and treatment with medications. Another complication following surgery for Crohn's disease in which the terminal ileum has been removed is the development of excessive watery diarrhea. This is due to an inability of the ileum to reabsorb bile acids after resection of the terminal ileum.

In some cases of SBS, intestinal transplant surgery may be considered; though the number of transplant centres offering this procedure is quite small and it comes with a high risk due to the chance of infection and rejection of the transplanted intestine.

Alternative medicine
More than half of people with Crohn's disease have tried complementary or alternative therapy. These include diets, probiotics, fish oil and other herbal and nutritional supplements. The benefit of these medications is uncertain.
 * Acupuncture is used to treat inflammatory bowel disease in China, and is being used more frequently in Western society. There is insufficient evidence to recommend the use of acupuncture, though further studies are warranted.
 * Homeopathy is frequently used in Germany as a treatment for Crohn's disease, though no clinical trials exist that demonstrate it is effective.

Prognosis
Crohn's disease is a chronic condition for which there is currently no cure. It is characterised by periods of improvement followed by episodes when symptoms flare up. With treatment, most people achieve a healthy weight, and the mortality rate for the disease is relatively low. However, Crohn's disease is associated with an increased risk of small bowel and colorectal carcinoma, including bowel cancer.

Epidemiology
The incidence of Crohn's disease has been ascertained from population studies in Norway and the United States and is similar at 6 to 7.1:100,000. The Crohn's and Colitis Foundation of America cites this number as approx 149:100,000; NIH cites 28 to 199 per 100,000. Crohn's disease is more common in northern countries, and shows a higher preponderance in northern areas of the same country. The incidence of Crohn's disease is thought to be similar in Europe but lower in Asia and Africa. It also has a higher incidence in Ashkenazi Jews and smokers.

Crohn's disease has a bimodal distribution in incidence as a function of age: the disease tends to strike people in their teens and 20s, and people in their 50s through to their 70s, and ages in between due to not being diagnosed with Crohn's and being diagnosed instead with irritable bowel syndrome (IBS). It is rarely diagnosed in early childhood. It usually strikes females who are pediatric patients more severely than males. However, only slightly more women than men have Crohn's disease. Parents, siblings or children of people with Crohn's disease are 3 to 20 times more likely to develop the disease. Twin studies show a concordance of greater than 55% for Crohn's disease.

History
Inflammatory bowel diseases were described by Giovanni Battista Morgagni (1682–1771) and by Scottish physician T. Kennedy Dalziel in 1913.

Ileitis terminalis was first described by Polish surgeon Antoni Leśniowski in 1904, however, due to the precedence of Crohn's name in the alphabet, it became later to be known in the worldwide literature as Crohn’s disease. Only in Poland it continues to be named Leśniowski-Crohn’s disease. Burrill Bernard Crohn, an American gastroenterologist at New York City's Mount Sinai Hospital, described fourteen cases in 1932, and submitted them to the American Medical Association under the rubric of "Terminal ileitis: A new clinical entity". Later that year, he, along with colleagues Leon Ginzburg and Gordon Oppenheimer published the case series as "Regional ileitis: a pathologic and clinical entity".

Research
Researchers at University College London have questioned the wisdom of suppressing the immune system in Crohn's, as the problem may be an underactive rather than an overactive immune system: Their study found that Crohn's patients showed an abnormally low response to an introduced infection, marked by a poor flow of blood to the wound, and the response improved when the patients were given sildenafil citrate.

Recent studies using helminthic therapy or hookworms to treat Crohn's Disease and other (non-viral) auto-immune diseases seem to yield promising results.

Numerous preclinical studies demonstrate that activation of the CB1 and CB2 cannabinoid receptors exert biological functions on the gastrointestinal tract. Activation of CB1 and CB2 receptors in animals has shown a strong anti-inflammatory effect. Cannabinoids and/or modulation of the endocannabinoid system is a novel therapeutic means for the treatment of numerous GI disorders, including inflammatory bowel diseases like Crohn's disease.


 * Methotrexate is a folate anti-metabolite drug that is also used for chemotherapy. It is useful in maintenance of remission for those no longer taking corticosteroids.
 * Metronidazole and ciprofloxacin are antibiotics used to treat Crohn's that have colonic or perianal involvement, although, in the United States, this use has not been approved by the Food and Drug Administration. They are also used for treatment of complications, including abscesses and other infections accompanying Crohn's disease.
 * Thalidomide has shown response in reversing endoscopic evidence of disease.
 * Cannabis-derived drugs may be used to treat Crohn's Disease with their anti-inflammatory properties. Cannabis-derived drugs may also help to heal the gut lining.