At first glance, it might seem like inflammatory bowel disease (IBD) and ankylosing spondylitis (AS) don’t have much in common. But despite their different areas of focus, these two conditions regularly occur at the same time.

Inflammatory bowel disease (IBD) is the collective term for ulcerative colitis (UC) and Crohn’s disease (CD), two separate conditions that cause chronic inflammation in the gastrointestinal (GI) system. While UC is the most common of the two, more than 3 million people in the United States live with some form of IBD.

Ankylosing spondylitis (AS) is a type of arthritis affecting the spine and sacroiliac joints (the joints of your pelvis). Along with non-radiographic axial spondyloarthritis (nr-axSpA), AS is one of two subtypes of axial spondyloarthritis (axSpA), a type of inflammation that affects the skeletal joints of your pelvis and trunk.

While a GI disease and an arthritic condition don’t sound like they’d have much in common, living with one of these conditions may make it more likely you’ll be diagnosed with the other.

IBD and AS are common comorbidities. Comorbidities are conditions occurring at the same time, and common comorbidities are those that occur together at a higher rate than they do separately in the general population.

The comorbidity between AS and IBD is bidirectional. This means living with AS may make it more likely you’ll be diagnosed with IBD, and living with IBD may increase your chances of being diagnosed with AS.

According to a 20-year follow-up study from 2017, people who received a diagnosis of IBD were more likely to report ankylosing spondylitis, axSpA, and inflammatory back pain in the 20 years after their diagnosis.

A systematic research review from 2023 also found people diagnosed with UC were more likely to develop AS in the future.

When it comes to risk factors, a 13-year population-based cohort study from 2020 indicated a higher risk of IBD among people with AS under the age of 40 years.

The reason behind the link between AS and IBD is not fully understood, but experts theorize that shared genetic pathways play an important role. Both AS and IBD are considered immune-mediated conditions, meaning unusual immune system activity is involved in their development and progression.

Both the 2017 study and the 2023 research review discuss a genetic link between IBD and AS through the HLA-B27 gene, and more shared pathways are being investigated. One study from 2023, for example, indicated 25 potentially shared genes between UC and AS.

Under this theory, it’s possible that the same genetic factors contributing to dysfunctional immune activity naturally increase the risk for both IBD and AS.

Types of IBD most commonly associated with AS

Although UC is the most common form of IBD, research from 2023 notes AS is more common in Crohn’s disease, and AS is suspected to affect approximately 10% of people diagnosed with IBD, overall.

No direct link has yet been established showing AS directly causes IBD or vice versa, but IBD may be more common in AS than AS is in IBD.

IBD is considered an extraarticular manifestation in AS, affecting up to 50% of people with this diagnosis. Doctors use the term “extraarticular” to describe co-occurring conditions or symptoms in other areas of the body when the primary diagnosis is joint-related.

However, this doesn’t mean AS causes IBD. It simply means that IBD symptoms are frequently seen alongside an AS diagnosis.

Treating AS and comorbid IBD requires a diverse therapeutic approach that takes into consideration both stand-alone diagnoses. Each condition can involve medications and lifestyle changes, but the focus of these therapies is specific to AS or IBD.

AS is typically treated with medications that target joint pain and inflammation, such as disease-modifying antirheumatic drugs (DMARDs), nonsteroidal anti-inflammatory drugs (NSAIDs), and biologics, medications that mimic human immune molecules.

IBD is also treated with biologics and medications that manage inflammation, but these drugs target the GI system, specifically.

Both conditions may benefit from lifestyle changes, but IBD adjustments may be more dietary-focused, while AS recommendations might focus on maintaining mobility.

Because AS does not directly cause IBD, and IBD does not directly cause AS, treating only one condition may not significantly improve the other.

However, crossover benefits are possible, according to 2023 research. Researchers found adding biologic therapy to an AS treatment plan early on may lead to a higher rate of IBD symptom remission.

Ways to manage co-occurring AS and IBD

Navigating the complexity of a dual diagnosis can be challenging, but there are steps you can take to help make the experience less overwhelming. Consider the following options for managing AS and IBD:

  • learning more about IBD and AS to help you feel in control of your diagnosis
  • keeping a symptom journal or log to track your experiences with both conditions
  • using electronic reminders and schedulers to stay on top of appointments and medication refills
  • discussing with your doctor how your medications may affect each condition
  • prioritizing self-care, such as developing stress relief techniques and relaxation methods
  • focusing on healthy lifestyle habits to improve your general health and well-being
  • joining support groups to share the experiences and successes of others with AS and IBD
  • speaking with a mental health professional to help guide you through the challenges related to living with chronic illnesses

Ankylosing spondylitis (AS) and inflammatory bowel disease (IBD) are immune-mediated conditions and common comorbidities. Living with AS may increase your chances of experiencing IBD, and being diagnosed with IBD may increase the likelihood you’ll be diagnosed with AS.

While both AS and IBD are treatable, prioritizing self-care, focusing on health-promoting lifestyle habits, and leaning into an established — or creating a new — support network can help you manage life with this dual diagnosis.