Crohn's Disease

Medically reviewed by Carina Fung, PharmD, BCPPS

What is Crohn's Disease?

Crohn’s disease1 is a form of inflammatory bowel disease (IBD) in which parts of the gastrointestinal (GI) tract (specifically, the colon, and, less frequently, the small intestine) become inflamed. This can, in turn, lead to chronic abdominal pain, diarrhea, weight loss, malnutrition, and fatigue. When left untreated, Crohn’s disease can be life threatening.

Named after gastroenterologist Burill Bernard Crohn in 1932, Crohn’s disease has been studied for nearly 100 years. However, the exact causes of the disease remain poorly understood. It is suspected that Crohn’s disease may result from a combination of hereditary and/or environmental factors. The disease may also be exacerbated by a poor or weakened immune system.

There is currently no cure for Crohn’s disease, although several treatments and medications have been effective in helping patients lessen their symptoms (and, in some cases, achieve remission).

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Crohn’s disease vs. ulcerative colitis

Both Crohn’s disease and ulcerative colitis are forms of inflammatory bowel disease (IBD) that lead to chronic inflammation of different parts of the GI tract. Both diseases display similar symptoms and can affect anyone of any age or biological sex. The exact causes of both forms of IBD remains unknown.

That being said, there are also several prominent differences2 between Crohn’s disease and ulcerative colitis:

  • Ulcerative colitis only appears in the colon, while Crohn’s disease can appear anywhere between the mouth and anus in the GI tract (although it is most commonly found in the colon and a portion of the small intestine).
  • Ulcerative colitis typically manifests as a continuous region of inflammation, whereas Crohn’s disease tends to have a patchy spread, where inflamed tissue can be found next to healthy tissue.
  • Ulcerative colitis only affects the innermost lining of the colon, whereas Crohn’s disease can penetrate deeply into every layer of the bowel walls.

It is also possible to have a form of IBD that displays both the symptoms of ulcerative colitis and Crohn’s disease. Approximately 10% of all IBD cases present with both sets of symptoms, a condition referred to as indeterminate colitis.

How common is Crohn's disease?

According to the Crohn’s & Colitis Foundation, Crohn’s disease affects about 1.3% of Americans3 (3 million people). Crohn’s disease can occur at any age, but is most often diagnosed between the ages of 20–30. Crohn’s disease can also affect people from any ethnic background, but is most commonly diagnosed in Caucasians.

According to the Centers for Disease Control and Prevention (CDC), only 2 million American adults4 were reported to have Crohn’s Disease in 1999. This may be due to underreporting in the past due to a lack of understanding surrounding the disease and its symptoms.

Aside from Hispanic and non-Hispanic whites, the following groups of people5 are more likely to report having IBD in general:

  • Anyone aged 45 or older
  • Anyone living in poverty or who is not currently employed
  • Anyone with less than a high school level of education
  • Anyone living in suburban areas

Unfortunately, researchers have yet to establish6 why these factors are associated with higher rates of Crohn’s disease.

Crohn's disease causes

The difficulty with predicting the prevalence of Crohn’s disease arises from the uncertainty surrounding its heredity and underlying causes. While certain genetic components have been linked to an increased risk of IBD and 28% of people diagnosed with IBD7 have relatives who also have the disease, it is not possible to predict with certainty who will develop Crohn’s disease based on family history alone.

In the past, researchers believed that Crohn’s disease may have had an environmental trigger or cause (rather than a genetic or hereditary one). Currently, the prevailing theory is that Crohn’s disease is caused by a combination of genetic, environmental, and lifestyle factors, many of which remain unknown.

That being said, after nearly a century of research into the disease, several risk factors have been identified as increasing the likelihood of having Crohn’s disease.

Risk factors for Crohn's disease

The most well-documented risk factors for Crohn’s disease are genetic. According to the U.S. National Library of Medicine, many of the genes involved in Crohn’s disease—such as NOD2, ATG16L1, IL23R, and IRGM—are involved in immune system regulation and function. These genes produce proteins8 that help the immune system recognize and respond appropriately to the billions of gut bacteria in the lining of the GI tract.

Under normal conditions, these proteins help white blood cells identify and destroy harmful pathogens (foreign bodies). However, variations or mutations in these genes and the proteins they encode may lead to an exacerbated immune response to healthy bacteria, as well. This, in turn, may lead to the chronic inflammation characteristic of Crohn’s disease.

There are at least 200 identified genetic variations of these genes that may contribute to Crohn’s disease. It is believed, however, that this represents only a small percentage of the complex genetic factors behind Crohn’s disease.

Environmental and lifestyle factors have long been suspected to play a role in the disease pathway as well, although they are poorly understood. Cigarette smoking, in particular, has been linked to an increased risk for a number of health complications, one of which is Crohn’s disease. Notably, Crohn’s disease is also diagnosed more frequently in urban and suburban communities, suggesting that increased industrialization, specific diets, and even sanitation practices may lead to an increased risk for the disease.

The role of diet in this disease has also been studied extensively in Crohn’s disease patients. But because Crohn’s disease can manifest differently in different patients, dietary inflammation triggers often vary widely from person to person well. As a result, the exact relationship between diet and Crohn’s disease remains unclear.

That being said, certain types of9 food can certainly aggravate the symptoms of Crohn’s disease, such as chronic inflammation. Specifically, diets low in dairy, fat, and fiber have been found to lead to better quality of life in Crohn’s disease patients. “Problem” foods, such as spicy dishes, alcohol, and caffeine, may also worsen symptoms of the disease.

Crohn's disease symptoms

All inflammatory bowel diseases display similar symptoms. Crohn’s disease, in particular, can affect any part of the GI tract between the mouth and anus. Most Crohn’s disease patients, however, present with a combination of the following mild-to-severe symptoms10:

  • Chronic inflammation of the ileum in the small intestine (the last section of the small intestine before the colon)
  • Chronic inflammation of the colon
  • Abdominal pain and cramping
  • Reduced appetite and weight loss
  • Blood in the stool
  • Mouth sores
  • Diarrhea
  • Fever
  • Fatigue

In severe cases of Crohn’s disease, the following symptoms may also be observed:

  • Inflamed skin, eyes, and joints
  • Inflamed liver or bile ducts
  • Delayed sexual development (when diagnosed in children)

If you or a loved one is experiencing these symptoms, it’s important to see your healthcare provider. They will be able to determine the correct diagnosis and best course of treatment.

Complications from Crohn's disease

When left untreated, Crohn’s disease can lead to life-threatening complications. For most patients, Crohn’s disease complications begins to manifest in several ways, namely:

  • Bowel obstruction: Parts of the bowel can scar and become narrower, which may obstruct the passage of stool.
  • Ulcers: Crohn’s disease patients may experience open sores anywhere in their GI tract, although they are most commonly observed in the mouth, anus, and/or near the genitals (i.e., the perineum).
  • Fistulas: Whenever an ulcer goes through an intestinal wall, the resulting formation is called a fistula: an abnormal, unintended connection between two different body parts.

Fistulas may lead to severe complications. For example, if a fistula forms between the bowel and any other part of your body, stool may drain directly into your body rather than exiting through the anus. This, in turn, could lead to severe toxicity and illness. In other cases, a fistula may become infected and form an abscess, which can become life-threatening if left untreated.

  • Anal fissures: Anal fissures—tiny tears in the soft tissue lining the anus—are vulnerable to repeated infection. Anal fissures are painful, and may also become perianal fistulas.
  • Malnutrition: Because the immune system of Crohn’s disease patients inappropriately targets “good” gut bacteria in the small intestine and colon (both of which are major sites of nutrient absorption), malnutrition is a common side effect of the disease. Typically, Crohn’s disease patients have insufficient iron and B-12 intake.
  • Colon cancer: As with any chronic complication of the colon, Crohn’s disease increases a patient’s risk of developing colon cancer. Generally, Crohn’s disease patients are advised to undergo colonoscopies once every 10 years beginning at age 50, although individuals diagnosed with Crohn’s disease at a younger age typically undergo colonoscopies, as well.
  • Other complications: The literature surrounding Crohn’s disease suggests that it may also lead to an increased risk of other types of cancer, such as lymphoma and skin cancers. Crohn’s disease has also been linked to anemia, skin disorders, osteoporosis, arthritis, and gallbladder or liver disease, although these relationships are poorly understood.

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