What Is Ankylosing Spondylitis? Causes, Symptoms, and Treatment

Definition

Ankylosing spondylitis, or AS, is a type of arthritis that affects the spine and the sacroiliac (SI) joints, where the spine meets the pelvis. It can also affect other joints and cause inflammation in the areas where tendons attach to bones. In severe cases, it can cause decreased range of motion in the spine, changes in posture, and chronic pain.

AS is an autoimmune condition, meaning it’s caused by the body’s own immune system reacting to healthy parts of the body. Experts used to think that AS was up to 9 times more common in men, but this is no longer the case. Men are more likely than women to show spine damage on X-rays, making them more likely to receive a diagnosis. With newer diagnostic criteria to account for this, experts believe men and women are affected equally.

It’s estimated that AS affects approximately 1% of adults in the U.S. But this may vary depending on location and the population studied. 

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Ankylosing spondylitis symptoms

The symptoms of AS depend on the affected areas of the body, which varies from person to person. Also, as with many autoimmune diseases, fatigue (extreme tiredness) is a problem for most people with AS. Symptoms usually begin before age 45.

Low back pain

Low back pain and stiffness are the most common symptoms of AS. Most people (at least 80%) experience back pain as their first symptom. Low back pain due to AS:

• Starts gradually

• Improves with exercise

• Doesn’t improve with rest

• Is worse at night

• May travel down into the buttocks 

Joint pain

Although the spine is most commonly affected, inflammation from AS can affect other joints. It can also cause inflammation where tendons attach to bones. This means AS can cause pain and stiffness in the following areas:

• Hips

• Knees

• Ankles

• Shoulders 

• Ribs/chest

Coexisting conditions 

People with AS often have other autoimmune disorders that affect other parts of the body: 

• Eyes: One in four people with AS have uveitis, which can cause eye redness, blurry vision, and sensitivity to bright light. 

• Abdomen: Inflammatory bowel disease, such as Crohn’s disease and ulcerative colitis, occurs in 6% to 14% of people with AS. This can cause abdominal pain and changes in bowel movements.

• Skin: Almost 10% of people with AS also have psoriasis.

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What causes ankylosing spondylitis?

It’s unclear exactly what causes AS to start. Researchers believe that a complex combination of genetics and environmental factors causes AS. They’re investigating how risk factors (more on this below) might affect people who are susceptible.

There is a strong genetic component to AS, specifically involving a gene called HLA-B27. But only a small percentage of people with HLA-B27 get AS. And at least 10% of people with AS don’t have HLA-B27. So, even though there’s a connection, it’s not the only cause.

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What are the risk factors of ankylosing spondylitis?

Risk factors aren’t causes but rather things that make you more likely to develop AS. Risk factors for AS include:

• Below age 45

• Genetics (HLA-B27) 

• Smoking

• Gut microbiome changes

The HLA-B27 gene is more common in people with white Northern European backgrounds than in other ethnic groups. Researchers believe this gene somehow changes the gut microbiome (the trillions of bacteria in your gut). But more research is needed to understand this relationship.

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How is ankylosing spondylitis diagnosed?

A specific test for AS doesn’t exist. Because of this — and the fact that back and joint pain are common among adults — it can take years for people with AS to get a diagnosis.

Getting a diagnosis often requires a combination of your:

• Symptoms

• Medical history

• Family medical history

• Physical examination

• Imaging tests (X-rays and/or MRI)

• Bloodwork 

X-rays often show signs of inflammation at the SI joints, or sacroiliitis. But not all people with AS have typical X-ray findings. Some people have what’s called a “non-radiographic” version of the disease. This means that there are no signs or changes seen on an X-ray, which is often how the condition gets diagnosed. Sometimes an MRI, which is more sensitive than an X-ray, can show signs of non-radiographic AS. But not always.

Blood tests that look for inflammation can also be helpful when autoimmune diseases are a possibility. These include erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP). They alone can’t diagnose or rule out AS, but they can provide extra information. 

Testing for HLA-B27 may also help. It’s not a diagnostic test. Rather, it’s a piece of the puzzle that can help to get a diagnosis. Remember: A positive HLA-B27 test doesn’t mean you have AS, and a negative test doesn’t mean you don’t. 

Your primary care provider can order some or all of these tests. But you may also need to see a rheumatologist to help with diagnosis. This is someone who specializes in diagnosing and treating autoimmune conditions.

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Progression of ankylosing spondylitis

Symptoms of AS usually begin in early adulthood. It’s common to first experience low back pain and stiffness. When symptoms first start, there may not be significant changes on imaging tests, especially X-rays. MRIs are more sensitive at finding subtle changes, such as inflammation near the sacroiliac joints.

Without treatment, inflammation usually continues. The body responds by creating new bone in certain areas. This can lead to areas of bone growth where it shouldn’t be. It can happen in the rib cage and at places where tendons attach to bones.

This can also cause “bamboo spine,” when the spine looks like a stick of bamboo due to bone growth over the discs between the vertebrae. This causes pain and limited motion in the spine. There’s also an increased risk of vertebral fractures and nerve compression.

Other possible complications include:

• Osteoporosis

• Increased risk of cardiovascular disease

Amyloidosis (a condition of abnormal protein buildup in the organs)

Treatments for ankylosing spondylitis

People who receive a diagnosis of AS will likely be treated by a rheumatologist. The goals of AS treatment are to:

• Reduce symptoms

• Maintain motion in the spine and joints

• Prevent permanent changes in posture

• Help people live well and keep their independence

Medications are typically recommended first to help with pain and inflammation (more on this below). 

Exercise also helps. For people with AS, it can reduce symptoms and inflammation. Research suggests that a physical therapy or home exercise program can help lessen pain and improve function.

If you are new to either exercise or AS, it’s a good idea to speak with your healthcare team before starting a new exercise program. Be sure to avoid spinal manipulation in order to avoid injury.

In some cases, AS worsens despite treatment with medication. If AS is severe and affects mobility or quality of life, surgery may be necessary. For example, hip replacement can improve motion and reduce pain related to hip arthritis. Spine surgery is usually reserved for people with severe posture changes. The decision to move forward with surgery should be made carefully and on an individual basis.

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Medications for ankylosing spondylitis

Medications that target inflammation or the immune system are often used to treat AS. Your rheumatologist can walk you through the possible side effects of each and help you decide which treatment is right for you.

Nonsteroidal anti-inflammatory drugs

Nonsteroidal anti-inflammatory drugs (NSAIDs) are often very effective for treating AS. They’re recommended as first-choice treatment. Examples include:

• Indomethacin (Tivorbex, Indocin)

• Naproxen (Naprosyn, Anaprox DS)

• Celecoxib (Celebrex)

• Diclofenac (Arthrotec)

Research suggests that all NSAIDs are equally effective. Some people will need daily treatment, whereas others may take medication only when needed.

Biologic medications

Biologic disease-modifying medications target specific molecules or cells in the inflammatory process. If treatment with NSAIDs doesn’t work well, treatment with a type of biologic called a tumor necrosis factor (TNF) inhibitor is recommended. Examples include: 

• Adalimumab (Humira)

• Certolizumab pegol (Cimzia) 

• Etanercept (Enbrel) 

• Golimumab (Simponi)

• Infliximab (Remicade) 

If a TNF inhibitor does not work well enough, other biologic options include secukinumab (Cosentyx) or ixekizumab (Taltz). 

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