What Causes Ankylosing Spondylitis? A Look Into this Rare Autoimmune Arthritis

If you’ve received a diagnosis of ankylosing spondylitis, there’s probably a lot on your mind. Will I ever feel better? What will happen to me in the future? And, why did this happen to me? This type of arthritis is a little bit different than other types of arthritis — including the causes.

What is ankylosing spondylitis?

Ankylosing spondylitis is a rare kind of arthritis that causes pain and stiffness in the spine and joints. Sometimes, other parts of the body can be affected, too. The condition affects about 0.5% of adults in the United States. 

Ankylosing spondylitis is an autoimmune condition. The immune system helps protect against things that don’t belong, like infections. The “auto” in autoimmune means “self,” so an autoimmune condition is when the body mistakes itself for something foreign. The result is too much inflammation.

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The most common symptom of ankylosing spondylitis is inflammatory back pain. This is a special kind of back pain that typically starts before age 45, is present when you wake up in the morning, and improves with exercise. Ankylosing spondylitis may also cause symptoms in other parts of the body. In severe cases, ankylosing spondylitis can cause stiffness and loss of flexibility in the spine, changes in posture, and chronic pain. Fortunately, ankylosing spondylitis is treatable.

What causes ankylosing spondylitis?

Experts aren’t exactly sure what causes ankylosing spondylitis, but they do know that different things play a role. 

Genetics

Generally speaking, ankylosing spondylitis starts with a “genetic predisposition.” This means that something in your genes (DNA inherited from birth parents) makes you more likely to develop ankylosing spondylitis one day than somebody else. The gene that leads to the highest risk is called HLA B27. 

If you have the HLA B27 gene, the risk of developing ankylosing spondylitis is about 20 times higher than someone who doesn’t have the gene. However, most people with the HLA B27 gene will actually never develop ankylosing spondylitis. This gene is found in up to 8% of people, but only 5% to 10% of them will develop ankylosing spondylitis.  

You also don’t have to have the HLA B27 gene to develop ankylosing spondylitis — 1 in 5 people with the condition don’t have this gene. So, testing for HLA B27 isn’t useful for confirming or ruling out the diagnosis. It’s just one piece of the puzzle.

The environment

Something from the environment can trigger the immune system, causing inflammation. Then, the immune system mistakes your own body for something foreign, leading to the autoimmune condition that is ankylosing spondylitis. 

Possible triggers for ankylosing spondylitis include:

• Infections

• Smoking

• Repetitive stress on the joints, or trauma to the joints

• Changes in the gut microbiome (healthy bacteria that live in the gut)

What are the risk factors for ankylosing spondylitis?

Some risk factors for ankylosing spondylitis include:

• The HLA B27 gene (see above), as well as other genes that aren’t routinely tested

• Having a first-degree family member (birth parent, sibling, or child) with ankylosing spondylitis 

• Having inflammatory bowel disease (like Crohn’s disease or ulcerative colitis) or psoriatic arthritis

• Altered gut microbiome

• Assigned male at birth

• Smoking

There aren’t currently any medications that can prevent the development of ankylosing spondylitis, but quitting smoking could decrease the risk. 

How quickly does ankylosing spondylitis progress?

It depends. Ankylosing spondylitis is different for every person who has it, and some people experience more severe symptoms than others. 

Research shows that when the diagnosis of ankylosing spondylitis is delayed, symptoms can be worse, and treatments might not work as quickly or effectively as they do in people who receive an early diagnosis. So the sooner you’re diagnosed and started on treatment, the better.

How do you treat ankylosing spondylitis?

The good news is that there are several treatments for ankylosing spondylitis. Nonsteroidal anti-inflammatory drugs (NSAIDs) like naproxen are typically the first step. However, most people will also require a biologic medication (like Humira or Cosentyx) to feel their best. These are immunosuppressive medications that decrease inflammation by turning off a piece of the immune system that’s too active.

Physical therapy, exercise, and stretches are also important parts of ankylosing spondylitis care. They work best when used in combination with medications. 

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Written by:

Samantha C. Shapiro, MD

Samantha Shapiro, MD, is a board-certified rheumatologist and internist with expertise in autoimmune and inflammatory conditions. She founded the division of rheumatology at Dell Medical School at The University of Texas at Austin.

Edited by:

Katie E. Golden, MD

Katie E. Golden, MD, is a board-certified emergency medicine physician and a medical editor at GoodRx.

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