Although they affect different parts of the body, there may be a link between ankylosing spondylitis (AS) and inflammatory bowel disease (IBD).

AS and IBD are both autoimmune disorders that cause ongoing inflammation. AS primarily affects the spine and joints, whereas IBD mainly affects the intestines.

Some people have both conditions, and they may have some shared underlying mechanisms or risk factors.

This article looks at the connection between AS and IBD, including their symptoms and how to manage both conditions.

Collage of a person holding their stomach due to IBD pain and another person rubbing their lower back due to ankylosing spondylitis.Share on Pinterest
Design by MNT; Photography by Westend61/Getty Images & Antonio Hugo Photo/Getty Images

It is unclear if AS directly causes IBD. However, it can cause intestinal inflammation, and people with one condition may be more likely to develop the other.

AS is a type of arthritis that primarily affects the spine, lower back, and sacroiliac joints. However, it can also cause symptoms and conditions in various organs outside the joints, known as extraarticular manifestations (EMs). This can include digestive symptoms.

According to research mentioned in a 2023 review, 5% to 10% of people with ankylosing spondylitis (AS) also have an inflammatory bowel disease (IBD) diagnosis, and over 70% have inflammation in the intestines.

Other estimates suggest that IBD may affect up to 50%Trusted Source of people with an AS diagnosis. Both may arise from underlying immune dysfunctions that affect multiple systems in the body.

A 2024 study states that research has not found a causal relationship between IBD and AS. However, people with IBD may have a higher risk of developing AS or other joint inflammation.

The incidence of AS in people with IBD has also increased in previous studies, from 0.3% to 3%.

Another study concluded that 5% to 20%Trusted Source of people with IBD develop other joint-related symptoms, such as peripheral arthritis and sacroiliitis, which is a characteristic of AS.

Scientists are still learning about why this is the case.

The potential link between AS and IBD is not fully understood. However, they are both autoimmune conditions, which means they occur because the immune system is mistakenly attacking healthy tissues.

Both AS and IBD also cause elevated levels of inflammatory markers, including cytokines such as tumor necrosis factor (TNF) and interleukins.

These are molecules that are important for activating the immune system, but when they become overactive, they can cause inflammation in various places around the body.

Another potential link is genetics. A variation in the HLA-B27 gene is common in people with certain types of inflammatory diseases, including arthritis and IBD.

This gene accounts for about 30%Trusted Source of the genetic risk for the condition. HLA-B27 may also interact with the gut microbiome, potentially worsening immune responses and leading to digestive complications.

However, this does not mean IBD and AS necessarily follow the same trajectories. A person with both conditions might find that one flares up while the other does not.

Both IBD and AS can cause some of the same symptoms, such as:

However, AS mainly affects the spine and joints. It typicallyTrusted Source develops slowly and may not cause many symptoms in the earlier stages. When they do develop, the symptoms of AS may include:

  • stiffness in the lower back, spine, and hips
  • chronic back pain
  • reduced flexibility
  • uveitis, which is a type of inflammation of the eyes

The symptoms of IBD can include:

Diagnosing AS generally involves a combination of physical exams, imaging studies, and laboratory tests. These may includeTrusted Source:

  • X-rays to detect changes to the spine and pelvis
  • MRI scan to examine the sacroiliac joints
  • ultrasound to show peripheral joint and tendon inflammation
  • blood tests to reveal markers of inflammation

A doctor diagnoses IBD through endoscopic procedures, imaging studies, and laboratory tests, includingTrusted Source:

  • a colonoscopy or sigmoidoscopy to see inside the intestines
  • a biopsy of the tissue to look for signs of damage
  • CT scans or MRIs to help assess inflammation in the intestines and detect fistulas
  • blood tests to indicate inflammatory markers
  • stool test to help rule out infections

There is currently no cure for either AS or IBD, but treatment can help relieve symptoms and manage both conditions.

However, it is important to note that some of the treatments for one condition may aggravate the symptoms of the other.

Doctors will recommend treatments based on each person’s circumstances and whether the conditions are mild, moderate, or severe. Options that could help both AS and IBD include:

  • Exercise: Physical exercise or physical therapy may improve joint function, alleviate stiffness, and address stress.
  • Dietary adjustments: For some, a balanced diet that includes anti-inflammatory foods may reduce overall inflammation, although the role of diet in IBD is unclearTrusted Source.
  • Aminosalicylate agents: These drugs are often the first treatment doctors try for IBD that is mild to moderate and only affects the rectum.
  • Corticosteroids: These drugs can reduce inflammation and may provide pain relief. For AS, doctors may use injections into the joint. For IBD that only causes infrequent flare-ups, doctors may give oral corticosteroids.
  • Anti-TNF biologics: Medications such as infliximab and adalimumab block TNF. According to a 2023 study, anti-TNF agents are a common choice of medication for treating AS and IBD at the same time. However, not all these drugs are suitable, as etanercept may exacerbate IBD.
  • JAK inhibitors: These drugs are another option for people with both conditions. They work by blocking a group of enzymes, affecting how the immune system works.
  • Surgery: Some people with IBD may need surgery to remove parts of the intestines that have become too damaged. In AS, surgery may include joint repair or replacement procedures.

Treatments that may not be suitable for people with both conditions include:

  • Nonsteroidal anti-inflammatory drugs (NSAIDs): NSAIDs can relieve pain and inflammation in AS but may irritate the gastrointestinal tract and worsen IBD symptoms in some people. This is important to note, as NSAIDs are often a first-line treatment for AS.
  • IL-17 inhibitors: IL-17 inhibitors can reduce spinal inflammation. However, doctors should not prescribe them for patients with IBD, as they may exacerbate the condition.

While doctors do not fully understand the links between AS and IBD, both may share some of the same risk factors or underlying causes.

For example, people with either condition may have similar genetic variants that increase the risk of autoimmune disorders.

Diagnosing and managing both conditions can be challenging, but certain treatments and lifestyle adjustments may provide relief for individuals with overlapping symptoms.

By understanding the possible links between AS and IBD, medical professionals can offer more comprehensive care, improving the quality of life for those managing both conditions.