Last updated:14th March 2018

What is AS?

AS is an inflammatory arthritis where the main symptom is back pain

It comes under the umbrella term of Axial Spondyloarthritis which includes:

Ankylosing Spondylitis (AS) :

Where changes to the sacroilliac joints and /or the spine can be seen on x-ray.

Non-radiographic axial spondyloarthritis:

Where x-ray changes are not present but you have symptoms.

Up to 70% of people with non-radiographic axial spondyloarthritis have visible inflammation in the sacroiliac joints and/or the spine when an MRI of the back is done. Inflammation is the body's reaction to injury or irritation, and can cause redness, swelling and pain.

30% of people in this group may not have any change visible on the MRI despite symptoms of back pain. In fact some of these patients may never show any inflammation on an MRI even if this is repeated later on in life. The reasons for this are still not well understood but may be due to how sensitive our methods to image the joints are.

 Download our leaflet for more information on axial spondyloarthritis.

Axial spondyloarthritis is still a relatively new term in rheumatology.

Many people have simply been told that they have ankylosing spondylitis, rather than axial spondyloarthritis or non-radiographic axial spondyloarthritis. Whichever diagnosis you have been given, all the information on the NASS website will be relevant to you and your condition.

Typical symptoms of AS include:

  • Slow or gradual onset of back pain and stiffness over weeks or months, rather than hours or days
  • Early-morning stiffness and pain, wearing off or reducing during the day with exercise
  • Persistence for more than 3 months (as opposed to coming on in short attacks)
  • Feeling better after exercise and worse after rest
  • Weight loss, especially in the early stages
  • Fatigue or tiredness
  • Feeling feverish and experiencing night sweats

What happens?

It's a painful, progressive form of inflammatory arthritis. It mainly affects the spine but can also affect other joints, tendons and ligaments.

Other areas such as the eyes and bowel can also sometimes be involved with AS.

  1. Inflammation occurs at the site where ligaments or tendons attach to the bone. This is known as enthesis.
  2. The inflammation is followed by some wearing away of the bone at the site of the attachment. This is known as enthesopathy.
  3. As the inflammation reduces, healing takes place and new bone develops. Movement becomes restricted when bone replaces the elastic tissue of ligaments or tendons.
  4. Repetition of this inflammatory process leads to further bone formation and the individual bones which make up your backbone (vertebrae) can fuse together.







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