What is Ankylosing Spondylitis?
Ankylosing Spondylitis (AS) is a disease involving inflammation, mainly of the joints of the spine and of the sacroiliac joints (where the bones of the spine meet the bones of the pelvis). This inflammation causes the affected joints to become swollen and tender, and reduces their range of motion.
Over time, this inflammation can lead to the fusing together of the bones of the spine and of the sacroiliac joints, causing stiffness and abnormal posture. However, current treatment options mean that this feared complication is fortunately becoming less frequent.
What is the cause?
The cause is not yet known. It is likely to be caused by several factors, including genetic and environmental influences, most of which have not yet been clearly identified.
However, the general view is that AS is an autoimmune disease. This means that it arises when the body’s own immune system mistakenly thinks that some of the body’s normal cells are intruders and tries to get rid of them by releasing certain substances that cause inflammation.
Research has found that this disease is more common in some families. The relatives of a person with AS – especially first and second-degree relatives – have an increased risk of developing the disease. It is particularly common in people who carry the gene known as HLA-B27. This suggests that there is a hereditary predisposition to developing the disease.
How common is it and who does it affect?
Ankylosing Spondylitis affects approximately half a percent to one percent of the adult population worldwide, spread approximately equally across mane and women. Symptoms usually begin to appear between the ages of fifteen and thirty-five.
What is the relationship between Ankylosing Spondylitis and Axial SpA?
Over the past ten years, the name axial spondyloarthritis (axial SpA) has become increasingly common. This is because an international group of experts in this field, known as the Assessment of SpondyloArthritis International Society (ASAS), now recommends that AS can be considered part of a broader and more widespread group of diseases called spondyloarthritis (SpA) and, more specifically, a type of axial SpA.
How is Ankylosing Spondylitis diagnosed?
Ankylosing Spondylitis is generally diagnosed by a Rheumatologist, as this is the specialist best able to recognise the early signs. While most people will experience episodes of lower back pain at some time in their life, these will generally be due to mechanical problems in or around the spine, such as muscle strain or disc prolapse. Only about five percent of adults under the age of forty who have lower back pain will have the specific chronic inflammatory back pain that is typical of ankylosing spondylitis.
What are the symptoms?
Early spinal symptoms
Ankylosing Spondylitis typically starts as lower back pain that begins gradually and is often described as dull. It is felt deep in the lower back or buttocks, and may radiate down the backs of the thighs. Frequently there is also back stiffness lasting half an hour or more after waking up, which usually get better with physical activity but returns after inactivity (such as sleep or prolonged sitting).
As the disease progresses, this initially intermittent back pain usually progresses to become more constant. Night-time back pain also becomes more common and troublesome, especially during the second half of the night, often making it necessary to get out of bed and move around.
Some people may also experience chest pain, due to the inflammation of the joints between the ribs and the backbone, which may lead to incorrect suspicion of heart or lung disease.
Later spinal symptoms
Over time, the chronic inflammation involved in AS results in the gradual formation of extra bone tissue. This leads to the development of bony ridges between spinal bones, eventually resulting in the fusing together of two or more spinal bones and/or of the sacroiliac joints.
When such fusing develops, it is usually obvious from the progressive stiffening and abnormal curvature of the spine, which can be easily seen on x-rays.
As the disease progresses, increasing stiffness of the spine is often accompanied by a reduction in back pain, which now becomes more mechanical in nature and is due to the resulting postural changes and limited range of motion rather than to the initial inflammation.
The fusing of bones usually takes several years to fully develop, but because it occurs at an unpredictable rate in different people, it is very difficult to give an accurate estimate of this risk in the early stages of the disease. This is an important aspect of the discussion about when to start targeted treatment, especially in people with longer-lasting AS, where a combination of spinal inflammation and fusing may be present at the same time.
- Peripheral Joints: Up to 25% of people with AS develop inflammation of peripheral joints (joints of the arms and legs).
- Anterior Uveitis: Around 30% – 40% of people with AS develop inflammation of the front part of the eye, known as anterior uveitis. It involves inflammation of the iris (the coloured part of the eye and sometimes the ciliary body (the part of the eye just behind the iris).
- Enthesitis: Inflammation of any site where a tendon attaches to the bone.
- Intestinal Symptoms: These include abdominal pain, ongoing loose stools and sometimes blood with the stool. The overlap between AS and inflammatory bowel disease occurs in 5% – 10% of people with AS.
- Skin: Around 10% of people with AS will develop Psoriasis, an autoimmune condition characterised by patches of red, dry, flaky, itchy skin.
- Osteoporosis and/or Fractures: Spinal osteoporosis is common in people with AS, where it is thought to be a result of spinal inflammation. The combination of spinal osteoporosis and spinal rigidity from the fusing of the spinal bones in people with AS results in a high risk of spinal fractures., which can occur with no or minimal trauma.
- Systemic Symptoms: Usually affects the whole body rather than a specific part of the body. Symptoms can include fatigue, anxiety and/or depression.
- Heart and/or Lung Disease: 15% (approx.) of people with AS are at risk of developing scarring of the upper parts of the lungs; 10% (approx.) of people with AS are at risk of developing scarring of the heart valve. These complications usually develop very late in the disease, are usually mild, do not cause significant symptoms or long-term problems unless other heart or lung conditions develop.
By Prof Hans Nossent MD, PhD, FRACP
Chair of Rheumatology & Musculoskeletal Medicine, UWA