Ankylosing spondylitis is the more severe subtype of axial spondyloarthritis (axSpA). It means the damage to your joints is visible on an X-ray. But some experts think this distinction isn’t clinically significant and consider axSpA as more of a spectrum.

Ankylosing spondylitis (AS) belongs to an umbrella of conditions known as axial spondyloarthritis (axSpA). In fact, spondylitis and spondyloarthritis are two names for the same type of joint disease.

Spondyloarthritis refers to a type of arthritis that affects your spine. It’s also a systemic disease, meaning that it may eventually affect other parts of your body.

Learn more about axSpA, including where AS fits in, and other important information to discuss further with a doctor.

AxSpA is a type of arthritis that primarily affects your spine. While axSpA may develop at any age, it primarily affects adults ages 20 to 40.

With axSpA, you may experience pain and swelling (inflammation) in your spine and the sacroiliac (SI) joints that connect your spine to your pelvis. Over time, it may affect other joints in your body along with your organs, eyes, and gastrointestinal (GI) tract.

A doctor may identify axSpA based on:

  • physical symptoms they observe or that you report
  • blood tests that measure systemic inflammation
  • imaging tests that look for bone damage

Since this type of arthritis runs in families, a doctor may also order genetic testing. Your risk of developing axSpA may be greater if you have a positive HLA-B27 gene result. But this isn’t definitive, as most people with this gene don’t develop axSpA.

Doctors classify axSpA into two different subtypes. The first is called radiographic axSpA, or AS. The second is known as nonradiographic axSpA.

While the two terms may be confusing, AS is the same as radiographic axSpA. That means the damage to your spine and SI joints has progressed to a point where you can see it on radiographic images (X-rays). In other words, AS is the more severe form of axSpA.

If the damage isn’t visible on X-rays, doctors refer to the condition as nonradiographic axSpA. If this is the case, it can mean you’re in the early stages of the disease. It can take up to 7 to 10 years for changes to be visible on an X-ray.

Still, it may be possible to have symptoms of AS that don’t show up on X-rays.

While AS (radiographic axSpA) may be visible on X-rays, nonradiographic axSpA isn’t. But spinal or SI joint damage from nonradiographic axSpA may be visible via magnetic resonance imaging (MRI). It can take a year or so for changes in your joints to show up on an MRI.

AS tends to be more prevalent in males. Nonradiographic axSpA tends to affect males and females equally. AxSpA is also less common in African Americans than in other racial groups.

AS also tends to develop at a younger age, typically before age 45. You may also be at a higher risk of developing AS if you have psoriasis or inflammatory bowel disease.

Despite such differences, the key symptoms of both types of axSpA are the same. Signs of this type of arthritis may include:

  • pain in your lower back, hips, and buttocks
  • pain that starts gradually but persists for more than 3 months
  • reduced pain with movement
  • pain that worsens at night
  • waking up with joint stiffness in the morning
  • fatigue
  • loss of appetite and unintentional weight loss
  • eye inflammation and possible vision changes
  • skin rashes

Related conditions

AS and axSpA both belong to the spondyloarthritis family of conditions. Unlike other types of arthritis, these conditions also cause enthesopathy — pain in the ligaments and tendons that attach to your bones.

Aside from axSpA, other types of spondyloarthritis include:

  • Enteropathic arthritis (EnA): This type of arthritis develops alongside inflammatory bowel diseases, such as Crohn’s disease and ulcerative colitis.
  • Peripheral spondyloarthritis: This subtype primarily affects joints in your arms and legs.
  • Psoriatic arthritis (PsA): In addition to joint inflammation and pain, this subtype develops in some people who also have psoriasis.
  • Reactive arthritis (ReA): This rare subtype, formerly called Reiter’s syndrome, is triggered by an infection.
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Since the only key difference between radiographic and nonradiographic axSpA is how it shows up on imaging tests, treatment for this condition is largely the same.

There’s currently no cure for axSpA, but treatment is important in reducing the risk of long-term complications. Such complications include reduced mobility, permanent joint damage, and organ damage.

A doctor may recommend a combination of medications to help treat the symptoms of axSpA while reducing the risk of progression. Options may include:

  • Pain relievers: These may include over-the-counter medications, such as acetaminophen (Tylenol) or ibuprofen (Advil).
  • Nonsteroidal anti-inflammatory drugs (NSAIDs): A doctor may recommend Advil or prescribe a stronger NSAID to reduce inflammation in addition to alleviating pain.
  • Corticosteroid injections: These may reduce pain and inflammation in knee and shoulder joints that axSpA affects. But doctors don’t recommend them for use in the spinal joints.
  • Disease-modifying antirheumatic drugs (DMARDs): Doctors often administer these as biologic injections. They may help axSpA that affects multiple joints throughout your body.
  • Janus kinase (JAK) inhibitors: JAK inhibitors are a type of DMARD that help to relieve symptoms by altering your body’s immune response.

In addition to medications, a doctor may also recommend regular exercise along with physical or occupational therapies to improve mobility.

Some people may seek chiropractic care to help relieve symptoms. But the Spondylitis Association of America suggests you avoid this if you have advanced axSpA and a fused spine or osteoporosis, as manipulating your spine could cause injury.

Talk with a doctor before undergoing any supplementary care.

How many people with nonradiographic axSpA go on to develop AS?

While the exact frequency is unknown, experts think that about 1.4% of people in the United States have axSpA, while 0.5% have AS. They also think that nonradiographic axSpA may be underdiagnosed, particularly in females.

How long does it take for nonradiographic axSpA to progress to AS?

The timeline for progression to AS may vary. However, as one 2018 review notes, about 12% of people with axSpA may develop AS within 2 years.

The only way to determine whether axSpA has progressed is through blood tests and imaging. Blood tests may show systemic inflammation. X-rays may reveal bone damage associated with AS.

Do either axSpa or AS cause osteoarthritis?

There are more than 100 types of arthritis, including spondyloarthritis and osteoarthritis (OA). While there’s some crossover between spondyloarthritis subtypes, this type of arthritis doesn’t cause OA.

While OA also causes pain and stiffness, it’s not due to systemic inflammation like other types of arthritis. Instead, OA is known as “wear and tear” arthritis due to its link to joint damage and degeneration from overuse. OA most commonly affects hand, knee, and hip joints.

But there’s a link between axSpA and osteoporosis. A doctor may consider screening for osteoporosis with a bone density scan, depending on your other risk factors.

AS is a type of axSpA that doctors can detect on an X-ray. While the clinical definition for AS differs from that of nonradiographic axSpA, the two subtypes share the same causes, symptoms, and treatment measures.

If you receive an axSpA or AS diagnosis, it’s important to discuss treatment options and possible complications with the doctor. It’s equally important to see a doctor if you have possible symptoms of axSpA, including persistent back pain and stiffness.