Inflammatory bowel disease, or IBD, is an autoimmune condition affecting the digestive tract. In individuals with inflammatory bowel disease, the immune system mistakenly attacks the bowels, causing inflammation. The inflammation can occur in all or part of the digestive tract.
Symptoms of inflammatory bowel disease
Symptoms of inflammatory bowel disease can vary, depending on the location and severity of inflammation.
Diarrhea, fatigue, and pain are the most common symptoms of inflammatory bowel disease. Low-grade fevers can also occur. Blood in the stool is possible, as well. Additionally, inflammatory bowel disease can affect the eyes, joints, skin, and liver.
Unsurprisingly, a reduction in appetite can often happen in people with inflammatory bowel disease. Not only does the reduced appetite potentially make it difficult to eat enough, but inflammatory bowel disease can also make it difficult for the body to properly digest and absorb nutrients. Because of this, weight loss, malnutrition, or vitamin deficiencies are fairly common among people with this disease.
It’s also possible for the symptoms of inflammatory bowel disease to change over time. During flare-ups, the symptoms might be severe, but it’s also possible for the disease to go into remission. When remission occurs, there may no symptoms at all for a period of time.
There are two main types of inflammatory bowel disease: Crohn’s disease and ulcerative colitis. The symptoms will vary depending on which specific type it is. There are additional types, but ulcerative colitis and Crohn’s disease are the most common and are considered the most classic.
Crohn’s disease can involve any part of the digestive tract.
Most often, though, the end of the small bowel and beginning of the large bowel are involved. Additionally, the inflammation can penetrate through all the layers of the intestines. Patches of healthy bowel are possible between the patches of diseased bowel.
If the inflammation associated with Crohn’s disease affects mainly the bowel wall, the bowel can narrow due to inflammation or scarring, or a combination of the two (called fibrostenosis or stenosis). If the bowel becomes too narrowed, it can become blocked. As a result of blockages, cramping, vomiting, and bloating can all occur. Ulcers can also occur as a result of these blockages.
When Crohn’s disease inflammation penetrates more deeply into the layers of the bowel, it can lead to ulcer formation. If the ulcers get deep, they can become tracts called fistulas, creating a passage between two spaces where there isn’t supposed to be one.
Usually, ulcerative colitis mostly affects the rectum and the upper part of the large intestine.
With this type of inflammatory bowel disease, the lining of the large intestine (also called the colon) and the rectum are afflicted with long-lasting inflammation and ulcers. Although ulcerative colitis is not associated with blockages, stenosis, or fistulas, this type of inflammatory bowel disease can be significantly more severe than Crohn’s disease.
A classification system is utilized to group together the different types of ulcerative colitis. The five classifications are determined by the location and severity of symptoms, although all five classifications still fall under the umbrella of ulcerative colitis. The five types of ulcerative colitis, in order from most mild to most severe, are:
- Ulcerative proctitis, which affects the rectum
- Proctosigmoiditis, which affects the rectum and the lower end of the colon (also called the sigmoid)
- Left-sided colitis, which affects the rectum, the lower end of the colon, and the descending colon
- Pancolitis, which can affect all of the colon
- Acute severe ulcerative colitis, which affects all of the colon
The symptoms can range from rectal bleeding only, as in ulcerative proctitis, to the acute pain, profuse diarrhea, fever, bleeding, and inability to eat associated with acute severe ulcerative colitis.
Causes of inflammatory bowel disease
Recent research suggests that a combination of factors contribute to someone developing inflammatory bowel disease.
The first, and most unchangeable, factor that contributes to inflammatory bowel disease is genetics. In studies of DNA samples from Europeans, over 160 genome variants have been identified as associated with an increased risk of inflammatory bowel disease. Recently, scientists have added a pool of DNA samples from people of East Asian, Iranian, or Indian descent. Thanks to the increased size of the DNA pool, an additional 38 regions of the genome were identified as influencing an individual’s susceptibility to inflammatory bowel disease.
Aside from the additional identified genomes, there were also a few differences in genetic susceptibility to inflammatory bowel disease. These differences in genetic susceptibility could be because of small differences in genome structure or environment.
Two of these differences are explained in an article published by the Wellcome Trust Sanger Institute:
“There are genetic variants in a gene called NOD2 which increase risk of IBD in Europeans that are simply not present in Asian populations… At another gene, called TNFSF15, the IBD risk-increasing variants are at a similar frequency in both Europeans and East Asians, but the variants seem to have a much stronger effect on disease risk in East Asia.”
Additionally, another study identified a higher incidence of inflammatory bowel disease among people who have inflammatory lung conditions, such as asthma or chronic obstructive pulmonary disease (COPD). This higher incidence could be due to similar inflammatory responses through the entire body’s immune system, or it could be connected to common factors in genetics or environment.
Other researchers found a gene that’s responsible for regulating a signaling molecule. Elevated amounts of this signaling molecule, called TNF, are associated with inflammatory bowel disease. In experiments with zebra fish, researchers found that a specific gene (uhrf1) acts as a “handbrake” on TNF production. When this gene is “turned off,” or inactivated, TNF production increases, as does the risk of inflammatory bowel disease. These researchers are now searching for ways to find similarly-functioning genes in humans.
Bacteria and inflammatory bowel disease
The bacteria present in the digestive system can also factor into the development of inflammatory bowel disease.
Lots of bacteria live in the gut. This is entirely normal. However, as diets and habits change, the ecology of bacteria in the gut (called the gut microbiome) can change, too. The gut microbiome can influence many aspects of health, from diabetes to liver disease to tumor risk. Scientists are working on identifying the healthy bacteria in the gut microbiome, as well as which bacteria are associated with the different types of inflammatory bowel disease.
Some of the bacteria in the gut microbiome may be inherited. It may also be influenced by antibiotic medications. One study has even found that it’s not necessarily the bacteria in the gut that lead to inflammatory bowel disease. Rather, it’s small particles called vesicles that are shed by the bacteria. These vesicles can penetrate the lining of the intestines and trigger an immune response.
However, a group of researchers has found that it’s possible to reshape the gut microbiome. By transplanting the microbiome of a healthy person into the gut of a person with inflammatory bowel disease, it may be possible to reshape the gut microbiome as a treatment for bowel disease.
Additionally, viruses have recently been identified as a possible influence in inflammatory bowel diseases. Viruses are present in the gut as well, forming the gut virome. A larger variety of viruses present in the gut virome has now been associated with inflammatory bowel disease.
Do you know someone with inflammatory bowel disease?
Image by Gisela Giardino via Flickr