Ankylosing Spondylitis and Crohn's: What's the Connection?

Medically Reviewed by Murtaza Cassoobhoy, MD on April 13, 2023
5 min read

Ankylosing spondylitis (AS) is a type of arthritis that causes swelling and pain in the spine and other joints. It also can affect other parts of your body, like your eyes and digestive tract. Doctors call these extra-articular symptoms, meaning they're outside of the joints.

If you have AS, you might be slightly more likely to get inflammatory bowel disease (IBD) and vice versa. The two most common types of IBD are Crohn’s disease and ulcerative colitis. Crohn's is a type of IBD that causes inflammation throughout the digestive tract. Ulcerative colitis causes inflammation in only the large intestine. Both conditions can cause stomach pain and other symptoms.

Up to 1 in 10 people with AS have Crohn's disease or ulcerative colitis. About 40% to 60% of people with AS have milder inflammation in their intestines that may or may not cause symptoms.

You may not know that you have inflammation in your gut until it gets worse. Up to 20% of people with symptomless, or “silent," inflammation will get Crohn's disease within the next 5 years.

If you have AS, you might want to talk to your doctor about getting tested for IBDs like Crohn’s disease. Treatment can slow down the progress of both conditions.

Crohn's disease doesn't cause AS and AS doesn't cause Crohn's disease, but sometimes people get both diseases. Experts think the two conditions have similar causes.

Both Crohn's and AS cause inflammation in the gut or joints, and sometimes other body parts, too. It's common for people with Crohn's disease and AS to also have inflammation in places like their eyes (uveitis) and skin (psoriasis).

It's possible that the immune cells that cause inflammation travel between the intestines, the joints, and other parts of the body.

Certain genes might set the stage for both diseases. Family members of people with AS are more likely to have Crohn’s disease, and vice versa. A few gene changes have been linked to both AS and Crohn's disease.

For example, the HLA-B27 gene codes for a protein that helps your immune system tell your own cells apart from harmful foreign substances. Up to 78% of people with AS and IBD have a different form of this gene. That variation may be one reason why their immune system mistakenly attacks healthy cells in their gut and joints. This is what causes the inflammation.

CARD15 (also called NOD2) is another gene linked to IBD. This gene carries the instructions for making a protein that helps your immune system work right. Changes to this gene might raise the risk for gut inflammation in people who have AS.

Right now, it's hard to know which people with AS will get Crohn's disease. Some studies have found that among people with AS, males and people with more active disease are more likely to have IBD. Those findings still need to be confirmed in future studies.

If you do get Crohn's disease, it may not be obvious. Stomach bugs and other common ailments also cause symptoms like diarrhea, belly pain, and tiredness.

Here are a few signs that you have Crohn's disease and not another GI issue:

  • You feel an urgent need to poop
  • You've lost weight
  • There's blood in your poop
  • You also have other symptoms, like mouth sores, fever, or night sweats

There's a good chance you won't have any symptoms of Crohn's disease. In most people, the inflammation is so mild that it only shows up during a test like an endoscopy or a biopsy of tissue from the intestine.

A fecal calprotectin test might show whether you're at risk for Crohn's disease or ulcerative colitis. This simple test measures the amount of calprotectin in a sample of your poop. A large amount of this protein in your poop is a sign that you have Crohn's disease.

You might already see a rheumatologist for AS. A gastroenterologist diagnoses and treats Crohn's disease.

Some of the same medicines you take to treat AS will also decrease inflammation and improve your symptoms of Crohn's disease. Other medicines help one of these conditions but not the other. A few AS treatments might make your Crohn's symptoms worse and are worth avoiding. It’s key that your rheumatologist and gastroenterologist communicate with each other to determine the best treatment plan for your overall health. 

Nonsteroidal anti-inflammatory drugs (NSAIDs). NSAIDs like ibuprofen (AdvilMotrin) are a common treatment for pain and inflammation in AS, but they aren't always a good fit for people with Crohn's disease. NSAIDs irritate the intestines. They could cause more sores and flares.

If you do have to take one of these medicines, your doctor will prescribe it with a proton pump inhibitor like omeprazole that prevents and treats gastric ulcers. 

Disease-modifying antirheumatic drugs (DMARDs).Another common treatment for AS and Crohn’s are DMARDs, medicines that calm the immune system to reduce inflammation. For example, sulfasalazine is a DMARD that treats both AS and Crohn's disease. Other DMARD options include methotrexate,azathioprine and 6-mercaptopurine

Biologic drugs. Biologics are another type of DMARD. They block proteins and other substances in your body that produce inflammation.

Tumor necrosis factor (TNF) inhibitors are a group of biologics that treat both IBD and AS. These medicines block a protein that causes inflammation in the joints in ankylosing spondylitis, and in the intestines in Crohn's disease.

Examples of TNF inhibitors are:

Your doctor might prescribe a TNF inhibitor if you have both AS and Crohn's disease and other DMARDs haven't helped your symptoms.

One TNF inhibitor, etanercept (Enbrel), works for AS but not for Crohn's disease. In fact, it might cause more IBD flares, or even trigger IBD in people who didn't have it before.

Steroids. Corticosteroids, or steroids, act on your immune system to bring down inflammation. Examples of these medicines are:

Doctors may prescribe steroids for some cases of moderate to severe Crohn's disease. But over time, they can have serious side effects. Steroid injections or pills are a treatment for arthritis in your arms, legs, fingers, or toes. These injections aren’t as helpful for arthritis in the spine.

Researchers are looking at other biologic drugs that might treat both AS and Crohn's disease.

JAK inhibitor. JAK inhibitors are not biologics but are also DMARDS. They come in pill form and target the Janus Kinase protein which plays a role in inflammation in the intestine and other organs. Tofacitinib (Xeljanz, Xeljanz-XR) has been approved to treat AS and ulcerative colitis.