Ankylosing Spondylitis and Axial Spondyloarthritis

What is Ankylosing Spondylitis and Axial Spondyloarthritis?


What is Ankylosing Spondylitis and Axial Spondyloarthritis?

These names can definitely be quite daunting and confusing, especially when the conditions are recently getting renamed as researchers find out more about them. To date, Axial Spondyloarthritis (AxSpA) and Ankylosing Spondylitis (AS) both fall under a group of conditions known as Spondyloarthritis. Let’s break this down.

The “Axial” and the “Spondylo-” refers to the spine and trunk, “Ankylosing” means stiffening or fusing, and the “-itis” means inflammation of the joints. There are many conditions under Spondyloarthritis, such as Psoriatic Arthritis or Reactive Arthritis, but we’ll focus more on AxSpA and AS in this blog.

To clear things up, Ankylosing Spondylitis (AS) is actually the same as Axial Spondyloarthritis (AxSpA), but only one of the 2 subgroups of AxSpA. AS is known as radiographic AxSpA, whereas the other subgroup is known as non-radiographic. There is growing acceptance that both subgroups of AxSpA are one disease, and that term alone is a sufficient diagnosis. This is because non-radiographic AxSpA can progress into radiographic AxSpA (or AS).

So what does radiographic vs non-radiographic mean?

Well, radiographic means there are visible changes in the scans you have done, like an MRI or x-ray. Radiographic AxSpA, i.e. Ankylosing Spondylitis, can show your spinal joints start to fuse. This can have a “bamboo-like” appearance or maybe even a “dagger-like” appearance as essentially more bone is being laid down at areas they’re not supposed to. This tends to be more at later stages, so early intervention is key for effective management. The joints mainly associated with AxSpA are the sacroiliac joints, which are the joints between your sacrum (that triangle bone where your tailbone attaches to) and your large pelvic bones. This is where Ankylosing Spondylitis normally starts, and if there is evidence of active inflammation of these sacroiliac joints and/or structural changes to the spine like bony outgrowths (at later stages if untreated), then that would be diagnosed as radiographic AxSpa, AKA Ankylosing Spondylitis. On the other hand, if there are no visible changes to your scans, then it would be non-radiographic AxSpA, provided you have fulfilled the other criteria of Spondyloarthritis (outlined under signs and symptoms).

What are the signs and symptoms of Axial Spondyloarthritis?

There’s a lot to look out for, but there are new classification criteria to help diagnose AxSpA (both AS and non-radiographic) developed by the Assessment of SpondyloArthritis (ASAS) International Society. It is highly likely you have AS if you satisfy the following criteria:

  • Under 45 years old
  • Chronic (long term of at least 3 months) back pain
  • Scans show inflammation of the sacroiliac joints

And at least one of the following (known as Spondyloarthritis features):

  • Inflammatory type back pain, i.e. morning stiffness longer than 1 hour, gradual onset, improvement with exercise, or pain that doesn’t get relieved with rest.
  • Arthritis in the peripheral joints, i.e. those not part of the spine, such as knees, fingers, toes, and hips.
  • Enthesitis – inflammation at the tendon and ligament attachments to bone, e.g. most commonly in the heel (so heel pain)
  • Dactylitis – inflammation of the fingers also known as “sausage digits”
  • Good response to NSAIDS, e.g. ibuprofen and diclofenac
  • Family history of Spondyloarthritis, e.g. AS, Psoriatic Arthritis, etc.
  • Inflammatory Bowel Disease (Crohn’s disease/ulcerative colitis)
  • Blood tests show the gene HLA-B27 and elevated CRP (an inflammatory marker)
  • Psoriasis (a skin condition characterised by red and crusty patches of skin covered with silvery scales)
  • Uveitis (inflammation of the eye, which includes redness, pain, and blurred vision).

However, if you didn’t have a scan done, you might have non-radiographic axial spondyloarthritis if you satisfy these criteria:

  • Under 45 years old
  • Chronic (long term of at least 3 months) back pain
  • Blood test shows you are HLA-B27 positive
  • At least 2 other Spondyloarthritis features (see above)

So what causes Axial Spondyloarthritis?

There is a huge genetic component in developing AxSpA (remember, that includes Ankylosing Spondylitis!) which is with the gene HLAB27. This gene is present in about 8% of the UK population and it belongs to a family of molecules that play a huge role in making sure your immune system is working properly. No one still actually knows how having HLA-B27 increases the risk of developing AS, but there are several theories. One of the more popular theories is the “arthritogenic peptide” theory, which describes how proteins from your own tissues get mistakenly interpreted as being foreign and so your body starts to attack itself. We refer to these types of conditions as an “autoimmune” disorder. The research is still ongoing and the uncertainty around this area has reflected on the limited treatments available to reverse or slow down the progression of symptoms.

One of the puzzling things about Ankylosing Spondylitis is that in many cases (between 19 to 62% depending on a study) patients can also have osteoporosis, a condition where your bone density is low. Consequently, this also increases the risk of fractures too! The reason why this is so puzzling is because Ankylosing Spondylitis also has the ability to lay down new bone, yet experience decreased bone density. It can be hypothesised that the new bone being laid is not as “organised” which can explain its fragility. Your bones are normally very well structured and that is reflected by how strong they are.
Another theory as to why people with Ankylosing Spondylitis can have their natural bone turnover disrupted is because this new bone formation is now potentially thought to be unrelated to inflammation. Normally, where there’s inflammation, as there would be in Axial Spondyloarthritis (remember the -itis stands for inflammation), bone formation is increased, but there have been some cases where despite treatment with TNF-alpha inhibitors (this reduces inflammation) still had persistent bone formation. This suggests that this new bone formation may also be a result from another mechanism in your body that may be a new target for treatment.

A third potential explanation as to why people with AS get osteoporosis is simply because they move less when they’re in pain! As we know, loading the bones in our body is important in supporting bone health. If people don’t move, the natural health of your bone begins to deteriorate. As they say, use it or lose it!

How is Ankylosing Spondylitis diagnosed?

There is no sure-fire way to diagnose Ankylosing Spondylitis like how you would diagnose a broken bone with an x-ray, or how you would diagnose high blood pressure with a sphygmomanometer. However, we can use a combination of case history taking, blood tests, and imaging to make an informed decision quite confidently. If anything, it is actually often missed, particularly at the early stages.

So what do we look for? Well, the signs and symptoms outlined above essentially. There have been tools developed to fasttrack patients with potential Axial Spondyloarthritis to see a rheumatologist (a doctor that deals with inflammatory/autoimmune problems), such as the SPADE tool, which is mainly used by first contact health care practitioners like osteopaths, GPs, or physiotherapists. Looking for clues during the case history, physical examination, and blood tests are the key to reaching a diagnosis.

One of the known patterns of Ankylosing Spondylitis is that it tends to develop in men more often than women, around 2.5 times more likely. However, do you remember there’s another subgroup called non-radiographic axial spondyloarthritis? Well for those who don’t have late-stage imaging changes such as the “bamboo spine” or “dagger spine”, the prevalence of non-axial spondyloarthritis is actually about the same between men and women. This can suggest there’s a lot of females with non-radiographic axial spondyloarthritis who may not be aware of it.

How is Ankylosing Spondylitis treated?

The first line of action is either conservative treatment or with “gentler” anti-inflammatory medication. Conservative treatment is treatment that relies on nothing else other than your own body to see if it can adapt better with either physical therapy, better education, exercise, and other related allied health professional fields. This is essential as it promotes your own body’s natural capacity to improve symptoms, and therefore minimising the need for medication with side effects.

One of the hallmark signs of having inflammatory back pain such as Ankylosing Spondylitis or non-radiographic axial spondyloarthritis is that it responds effectively to Non-Steroidal anti-inflammatory drugs (NSAIDs). Anti-inflammatory drugs do exactly what it says on the tin, they suppress inflammation. Common NSAIDs include ibuprofen, naproxen, and diclofenac. Over the counter NSAIDs from pharmacies or prescribed NSAIDs from your GP can help take the edge off the discomfort, however, stronger treatment may be needed if the progress from a combination of conservative treatment and NSAIDs has plateaued.

Stronger treatment involves biologic disease-modifying antirheumatic drugs (DMARDs) which aim to inhibit inflammation even more. DMARD medication can include injections called TNF-alpha inhibitors or anti-TNF. Tumour Necrosis Factor, or TNF, plays a fundamental role in your immune system and is involved with the inflammatory process of Ankylosing Spondylitis. With these injections, you really have to weigh up the pros and cons, as even though it can be very effective in suppressing the symptoms, inhibiting inflammation to this extent lowers the strength of your immune system dramatically. Inflammation isn’t always bad and is very important in your body to fight against infections.