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What is ankylosing spondylitis (AS)?

Ankylosing spondylitis (AS) is an inflammatory condition that affects the joints in your spine. Spondylitis simply means inflammation of the spine.

As part of the body's reaction to inflammation, calcium is laid down where the ligaments attach to the bones that make up the spine (vertebrae). This reduces the flexibility of your back and causes new bone to grow at the sides of the vertebrae. Eventually the individual bones of the spine may link up (fuse). This is called ankylosis and can be seen on x-rays.

Sections of the spine

Ankylosing spondylitis typically starts in the joints between your spine and pelvis, but it may spread up your spine to your neck. It can sometimes affect other parts of the body, including your joints, tendons or eyes.

Ankylosing spondylitis varies from person to person – your symptoms might be so mild that you can almost forget you have the condition, but if they’re more serious it could have a big impact on your quality of life.

Ankylosing spondylitis is one of a group of conditions known as 'spondyloarthritis' (pronounced as spond-ee-lo-arthritis). These conditions share many of the same symptoms.

What are the related conditions?

There are a number of conditions related to ankylosing spondylitis which have many similar symptoms:

  • Non-radiographic ankylosing spondylitis and undifferentiated spondyloarthritis (uSpA) have similar symptoms to ankylosing spondylitis but x-rays won't show the signs of damage to your joints. Sometimes people with these conditions are later diagnosed with ankylosing spondylitis.
  • Psoriatic spondyloarthritis is a form of psoriatic arthritis which occurs in association with the skin condition psoriasis. 
  • Spondyloarthritis associated with inflammatory bowel disease (or enteropathic arthritis) is related to bowel conditions such as Crohn's disease or ulcerative colitis. 
  • Reactive arthritis (which used to be known as Reiter's syndrome) is diagnosed when your arthritis is a reaction to an infection. 
  • Enthesitis-related arthritis is the name used when children and teenagers develop arthritis of the entheses, the sites where tendons and ligaments attach to bone.

Some doctors use the terms spondarthritis, spondyloarthropathy, spondyloarthritides or seronegative spondyloarthritis. These terms all describe types of arthritis belonging to the same group of conditions as ankylosing spondylitis.


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