What is inflammatory bowel disease?

Inflammatory bowel diseases are chronic relapsing disorders that cause inflammation within the gut, which damages the gut lining. This can lead to multiple health problems, such as difficulty absorbing nutrients, abdominal pain, and diarrhea, which for some people can be life-threatening. The vast majority of inflammatory bowel disease is due to either ulcerative colitis or Crohn’s disease.

Knowing that these disorders are types of bowel disease, it’s not that surprising that tissue damage occurs primarily in the lower portions of the gastrointestinal tract. However, a key difference is that although ulcerative colitis usually only affects the colon and rectum, Crohn’s disease starts in the bowels, but can subsequently occur in any part of your digestive system, even your mouth.

Your digestive system, also called the gastrointestinal tract, or gut has two main functions - digestion and absorption of nutrients. It is composed of several structures that are arranged linearly in your body, from top to bottom, starting with the mouth, followed by the esophagus, stomach, small intestine, large intestine (colon) and rectum, and ending with the anus. Each structure is adapted to perform specific functions. Digestion, or the breakdown of food begins in your mouth, where it is chewed and hydrated before you swallow it. As it passes through your digestive system, it is broken down by digestive enzymes into nutrients that are small enough to be absorbed into your bloodstream such as simple sugars and amino acids, the building blocks of carbohydrates and protein. Your stomach is like a dynamic storage tank; it not only holds and concentrates the food, but also churns it up with digestive enzymes, which start to digest protein, and sterilizes it in preparation for its journey through the small intestine where 90% of the digestion and absorption of nutrients occurs. Large quantities of water are secreted into the small intestine to help with the digestive process, much of which is later reabsorbed. Having passed through the small intestine, what’s left enters your colon where it is further digested and any nutrients that are produced are absorbed. Your colon also reabsorbs much of the remaining water, as well as processing and preparing waste products for elimination.

If we take a closer look at the colon, we see there are the same four layers that make up most of the gastrointestinal tract. These are: the mucosa, a mucous membrane made up of epithelial cells that forms the inner lining; the submucosa, a layer of connective tissue containing glands, blood and lymphatic vessels, and nerves; a thick muscle layer; and the serosa, which is the outer lining.

Gut microflora: your body co-exists with trillions of microorganisms, collectively called the microflora. These microbes colonize every surface that is exposed to the outside world, including your digestive tract. The number of bacteria steadily increases as you proceed down the digestive tract to the colon, which contains almost 70% of the microbes in your entire body. The bacteria in your colon help you in a variety of ways. For example, they digest components of food that has not been digested by your small intestine, train your mucosal immune system to be tolerant to beneficial microbes, prevent the growth of harmful bacteria, and produce hormones that regulate fat storage, and vitamins such as vitamin K. Each person’s microflora is unique and, if you are a healthy adult, generally fairly stable. However, infection and disease can destabilize the microflora, which disturbs the normal functioning of the gastrointestinal tract.

Mucosal immune system: your immune system has the important job of fighting off disease-causing organisms (pathogens) when they end up inside your body. In the gut, the mucosal component of your immune system has to eliminate any pathogens that are ingested, while at the same time tolerating the beneficial microbes in the microflora. This is achieved in several ways: 1) the mucosa itself is designed as a strong physical barrier that protects against pathogenic infection; 2) specific types of immune cells that are primed for attack, are held at strategic locations throughout the intestines; and 3) multiple immune adaptations make local immune responses less vigorous, preventing a chronic full blown immune response. Any inflammation that is triggered by the mucosal immune system as part of a normal immune response required to eliminate pathogenic microbes invading the gut is quickly controlled as the mucosal cells regenerate and repair. This is much like the swelling that may happen when; for example, you bump your knee on a chair. The resulting lump is due to local inflammation that subsides as your immune system repairs the damage.

Inflammatory bowel disease is caused by an inappropriate inflammatory response to normal gut microflora in people with a genetic predisposition, which may involve several different genes. Chronic intestinal inflammation develops due to persistent activation of the mucosal immune system. Various factors that potentially exacerbate inflammation and drive associated symptoms have been identified including:

A combination of these factors typically contribute to the development of inflammatory bowel disease.

Inflammation and tissue damage takes a different course in ulcerative colitis and Crohn’s disease:

Ulcerative colitis: the inflammatory response and mucosal damage are localized in the colon and almost always involve the rectum. The inflammation typically only occurs within the mucosal layer of the colon wall, but generally affects the entire length of the colon.

Crohn’s disease: although it most commonly affects the bowel, Crohn’s disease can involve any part of the gastrointestinal tract from the mouth to the anus. Diseased segments, called “skip areas” are typically separated by stretches of normal bowel. Tissue damage often extends past the mucosal layer right through to the serosa. As the tissue heals, it may produce an abnormal tunnel-like connection, known as a fistula, which connects the intestine to another organ or tissue. For example, an enterovesical fistula connects the intestines and the bladder, which may cause frequent urinary tract infections.

Like many other inflammatory diseases, ulcerative colitis and Crohn's disease are life-long diseases, presenting with “flares” of symptoms. The signs and symptoms of both diseases are generally similar, so if you have either of these diseases, you are likely to experience one or more of the following: diarrhea, fever and fatigue, abdominal pain and cramping, blood in your stool, reduced appetite, and weight loss. The severity of symptoms however, can vary widely. For example, while it’s possible you may only have rectal bleeding, it’s also possible you may experience severe pain, extreme diarrhea, bleeding, fever, and an inability to eat. For many people, inflammatory bowel disease has a severe impact on quality of life due to debilitating recurring symptoms that can interfere with work and career choices, social interaction, and physical intimacy.

In addition to symptom flares, inflammatory bowel disease can cause a variety of serious complications including severe intestinal bleeding from ulcers, perforation of the bowel, and malnutrition. Disease specific complications include toxic megacolon (a life-threatening, severe distention of the colon) and increased risk of colon cancer, which are more commonly associated with ulcerative colitis; and narrowing or obstruction of the bowel, fistulae, apthous ulcers (mouth ulcers) and perianal disease, which are more commonly associated with Crohn’s disease and contribute to a significantly increased risk of death. In addition to all of this, you may also be predisposed to other inflammatory disorders such as arthritis, skin conditions, inflammation associated with eye, liver, or kidney diseases, or bone loss, with arthritis being the most common.

Inflammatory bowel diseases occur due to complex interactions between your genes, your gut microflora, environmental factors, and malfunctions in your immune system. Different genetic abnormalities have been identified that cause defects in the mucosal barrier and immune responses, as well as preventing efficient bacterial clearance. Although the exact mechanisms are not yet known, a popular theory is that your mucosal immune system fails to down regulate inflammation after it has been activated in response to an environmental trigger in your gut, such as an acute infection, or continual use of non-steroidal anti-inflammatories (which can irritate the gut lining). As it turns out, many factors can stimulate or inhibit mucosal immune responses, including the types and proportions of different microbes in your microflora, your diet, smoking, stress, and exposure to non-steroidal antiinflammatories (which may irritate the lining of the gut). Smoking is particularly unusual, because although it exacerbates Crohn’s disease, it is protective against ulcerative colitis. However, it is worth noting that nicotine patches seem to be less effective at protecting against ulcerative colitis than cigarettes, suggesting additional factors are involved. Regardless of these facts, the harms caused by smoking far outweigh the benefits of quitting.

Around 5 million people are thought to have inflammatory bowel disease.${}^1$‍ It usually begins in early adulthood in otherwise healthy, active people, affecting males and females equally. More recently, it has been increasingly diagnosed in children, especially those with a family history of the disease. It occurs most commonly in Caucasians followed by Blacks, Hispanics and Asians, likely reflecting different genetic patterns of susceptibility in these different populations.${}^2$‍

Although there is not a lot of information available for many regions, we do know that the incidence and prevalence of inflammatory bowel disease is increasing around the world, and it is emerging as a global disease. It is most common in Europe and North America, where the prevalence has increased rapidly over the last 50 years; however it is also becoming increasingly common in other parts of the world, where countries have adopted a Western lifestyle.${}^1$‍

There are no known ways to prevent the onset of inflammatory bowel disease or its symptoms. Some people find that certain foods may exacerbate inflammatory bowel disease, especially when it is active. As such, you may want to try systematically eliminating certain things you eat from your diet to try to identify if this may be the case for you. In addition, you may want to consider stopping smoking if you have Crohn’s disease, as smoking leads to more severe disease his can be beneficial for people with Crohn’s disease.

Diagnosis: there is no single test to diagnose inflammatory bowel disease, so your healthcare provider will typically begin by ruling out other possible conditions such as irritable bowel syndrome, diverticulitis, or colon cancer. Several tests may be performed to help confirm the diagnosis including blood tests to identify anemia or infection, and to determine whether or not there is blood in your stool. Your healthcare provider may also recommend one or more procedures that provide images of the inside of your gastrointestinal tract. These may be endoscopic or imaging procedures. Endoscopy typically involves the insertion of a thin tube with a light and camera that provides images of the inner walls of your colon, small intestine, or stomach. Imaging may be by x-ray, computerized tomography or magnetic resonance imaging.

Treatment: Because inflammatory bowel diseases can develop via many different mechanisms the response to different treatments varies widely from one person to another, and is the reason why there is no universal treatment. There are currently five classes of medications available to treat inflammatory bowel disease. These are aminosalicylates, antibiotics, corticosteroids, immunomodulators, and biologic therapies. Aminosalicylates are often the first medicines used to treat inflammatory bowel disease. They alter immune responses, which reduces the acute inflammatory response in inflammatory bowel disease, but unfortunately they may also cause unpleasant intestinal side effects and headaches. If you have a fever, your healthcare provider may prescribe antibiotics to help control any infection, which may also help heal fistulas in people with Crohn’s disease. Corticosteroids may be given to reduce inflammation if you don’t respond to initial treatments, or in moderate to severe cases of ulcerative colitis or Crohn’s disease; however, they have numerous, sometimes severe side effects, so are usually reserved for short term use. Immunomodulators and biologic therapies reduce inflammation indirectly by suppressing the immune system. In some cases, two or more drugs may be prescribed together for best effect. These medications have widely varying side effect profiles that may affect their suitability on an individual basis. With these drugs in hand, two main treatment strategies, the step-up approach (the more traditional approach), and the top-down approach are often applied to guide therapy.

Step-up approach: The goal here is to reduce inflammation and symptoms, and prevent more serious complications from arising. The most suitable drug is often selected based on the severity of your symptoms. For example, if your symptoms are mild, you may start with aminosalicylates to reduce inflammation, and/or antibiotics to control any infection. However, if your symptoms are more severe you may start with a stronger drug such as a corticosteroid.

Top-down approach: The goal of this approach is to induce and maintain remission (absence of symptoms), particularly in Crohn’s disease. It involves using a combination of stronger medications early in the treatment process to aggressively treat the disease.

In addition to the medications that are used to control the disease process, various other drugs can help with diarrhea and pain, and dietary supplements can help overcome anemia (iron and vitamin B-12), and reduce the risk of osteoporosis that is associated with Crohn’s disease and steroid use (calcium and vitamin D). Finally, nutritional supplements may be given in a way that gives your bowels a break by temporarily reducing inflammation; for example, via a vein, known as parenteral nutrition. When drug therapy fails, the next step is surgery to remove damaged portions of the colon, or the entire colon if necessary.

Fecal microbiota transplantation, or stool transplant, is a procedure which takes stool from a healthy individual and places it in the colon of a recipient, with the goal of restoring a healthy microflora (the trillions of beneficial microbes that colonize your digestive system and help with the digestive process). This strategy has been successful for the treatment of patients infected with Clostridium difficile, a bacteria that causes diarrhea and sometimes life-threatening inflammation of the colon, with most people recovering after just one treatment. This procedure has recently been tested in a number of studies as a treatment for inflammatory bowel disease. Overall, 60% of patients with Crohn’s disease and 22% of patients with ulcerative colitis went into clinical remission after stool transplant.${}^4$‍ This approach may offer new hope for patients who have failed other treatments.