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What are the complications of Crohn's disease?

There are a number of disease complications that may occur with Crohn's disease.

1. Small Bowel Obstruction

The most common complication of Crohn's disease is a blockage of the intestine, usually the small intestine. The obstruction occurs because the inflammation in the intestinal wall eventually leads to scar tissue and narrowing of the lumen of the intestine (the cavity where digested material passes through). Over time, the lumen of the intestine becomes so narrow that even a small amount of inflammation can lead to closing of the lumen and result in a small bowel obstruction. The patient will often present with crampy abdominal pain, abdominal distention, nausea and, if severe enough, vomiting, lack of bowel movements, or inability to pass gas from below. In this situation, patients are usually told to stop eating, also known as bowel rest, which often leads to improvement. Intravenous fluids may be necessary. If the obstruction does not resolve or continues to recur despite medical therapy, surgery is usually indicated.

2. Fistulae

Crohn's disease may also cause inflammation and ulcers that tunnel through the affected intestine into surrounding organs, such as the skin (entero-cutaneous), bladder (entero-vesicle), vagina (rectovaginal), or other parts of the intestine (entero-enteric). The most common type of fistula is perianal, but that should be considered separately. Depending on the organ involved, fistulae are either defined as internal (bladder, intestine) or external (skin). Some fistulae that occur between the intestine and other parts of the intestine may not require any therapy. Fistulae to other organs may respond to medical therapy (immunomodulators), but may require surgery. Abscesses, or collections of pus, require drainage via surgery or via a drain placed by a radiologist. Sudden (acute) perforation is an indication for surgery. These patients present acutely with severe abdominal pain, rigid abdomen ("surgical abdomen"), fever, and chills. The symptoms can be similar to those of appendicitis.

3. Perianal Fistulae

These are the most common type of fistulae. Sometimes fistulas can be treated with medical therapy, but in some cases surgery may be necessary.


Mild thinning of the bones (osteopenia) occurs in up to 50% of patients with Crohn's disease, and more severe thinning of the bones ( osteoporosis) can occur in as many as 15% of patients. This complication is more common in those who have required steroid therapy, as well as in smokers, patients with more active disease, and those with low calcium and vitamin D intake. As a consequence, a special x-ray called a bone mineral density scan (DEXA) is recommended for patients who have been on steroids, are postmenopausal, have had a low-trauma fracture, or who have moderate-to-severe Crohn's disease. Patients with osteopenia/osteoporosis need to have a workup to rule out other causes of bone loss, including an overactive thyroid and low blood levels of vitamin D. All patients with Crohn's disease should be instructed to take supplemental calcium and vitamin D on a daily basis. Some patients may require the addition of special medications such as bisphosphonates to prevent further bone loss. Consultation with an endocrinologist or rheumatologist may be necessary.

5. Colon Cancer

There is an increased risk of  colon cancer in patients with Crohn's colitis. Risk factors include: more extensive disease, longer duration of disease, family history of colon cancer, or the concomitant presence of a disease called primary sclerosing cholangitis (PSC). Surveillance colonoscopies and biopsies are recommended every one to two years after the patient has had the disease for eight to ten years. The exception to this rule is in patients with PSC, who should start undergoing surveillance colonoscopies at the time of diagnosis.

6. Small Bowel Cancer

There is a clear increased risk of small bowel adenocarcinoma in patients with Crohn's disease, but it still remains an exceedingly rare complication. This type of cancer usually arises in areas of long-term active disease or structured bowel. There is no screening test that is currently recommended due to the rarity of this complication.

7. Anal Cancer

Anal cancer is a rare complication of long-standing perianal Crohn's disease.

8. Small Intestinal Bacterial Overgrowth

This complication typically presents with diarrhea, bloating, and abdominal cramping. It is caused by excessive growth of bacteria in the small intestine, often in the setting of strictures, fistulas, or loss (due to surgery) of the valve between the small intestine and colon (ileocecal valve). It is treated with antibiotics.

9. Nutritional Deficiencies

Nutritional complications can also be seen in patients with Crohn's disease, including deficiencies of proteins, calories, or vitamins. These deficiencies are caused by inadequate dietary intake, intestinal loss of protein, or poor absorption of nutrients as a consequence of the underlying inflammation. Vitamin B12 deficiency is often seen in patients with Crohn's disease who have undergone resection of a portion of their terminal ileum, the portion of the intestine that absorbs vitamin B12. Those same patients can also develop diarrhea from malabsorption of bile salts. Bile salts cause the colon to secrete instead of absorb water, resulting in diarrhea. Patients who undergo extensive ileal resection are at risk for fat malabsorption, which can lead to deficiencies of fat-soluble vitamins such as Vitamins A, D, E, and K. Vitamin D deficiency is also not uncommon in patients with Crohn's disease, often related to self-imposed restriction of dairy products due to perceived lactose intolerance. Malabsorption is another cause of vitamin D deficiency.

10. Kidney Stones

Diarrhea and fat malabsorption can lead to the development of kidney stones, which usually present with severe flank (lower lateral back) pain, nausea, vomiting, and blood in the urine.

11. Gallstones

Bile acid malabsorption may predispose to the formation of gallstones. Gallstones often remain asymptomatic, but can present with intermittent right sided upper abdominal pain. Patients with gallstones can also develop inflammation of the gallbladder (cholecystitis), infection of the ducts of the liver (ascending cholangitis), or inflammation of the pancreas (pancreatitis). Once gallstones become symptomatic, the gallbladder is usually surgically removed (cholecystectomy).

12. Extra-intestinal Manifestations (EIM)

Crohn's disease can affect organs outside the GI tract in up to 25% of patients. They are usually divided by organ system and by association with disease activity. The EIM are more common in patients whose disease involves the colon. Following is a list of possible sites that can be affected:

Pyoderma gangrenosum (skin complication) in a patient with Crohn's disease
  • Joints - Crohn's can affect the lower part of the spine or the peripheral joints (hips, knees, ankles, etc)
  • Skin - Two of the most common rashes associated with Crohn's disease are (1) erythema nodosum, which presents as painful raised red bumps, and (2) pyoderma gangrenosum, in which the skin develops ulcerations.
  • Eyes - Uveitis presents with eye pain and/or changes in vision and requires evaluation by an ophthalmologist. Episcleritis is painless redness of the conjunctiva and sclera (white part of the eye).
  • Liver - Fatty liver is the most common liver disease in patients with Crohn's disease, but primary sclerosing cholangitis (PSC) is the more severe associated form of liver disease. PSC is an inflammation of ducts in the liver that can eventually cause the liver to fail (cirrhosis). Patients with PSC are also at higher risk for cancer of the ducts of the liver.
  • Oral Ulcers

Contact Information

Inflammatory Bowel Disease Program
Digestive Disease Center
Beth Israel Deaconess Medical Center
330 Brookline Avenue
Boston, MA 02215