Ankylosing spondylitis is a lifelong (chronic) form of arthritis. It mainly affects the lower back but can spread higher up the spine. Other joints and other parts of the body are sometimes affected. How badly someone is affected varies widely.
There is no cure but treatment, including both physical therapy and medication, is available. One important point to remember - tell a doctor urgently if you have ankylosing spondylitis and develop a painful or red eye. An eye complication called uveitis can be serious but can be treated successfully if treatment is given promptly.
What is ankylosing spondylitis?
Ankylosing spondylitis (AS) is a persistent (chronic) arthritic (rheumatic) disease. It is not known what causes it. It mainly affects the spine and the joints that connect the bottom of your spine with your pelvis (sacroiliac joints). Sometimes other joints and other parts of the body are affected. The word ankylosing means joining together or fusing. The word spondylitis means inflammation of the spine. The type of inflammation in AS causes the affected joints to join together and become one bone.
Ankylosing spondylitis is a type of axial spondyloarthritis. See the separate leaflet called Axial Spondyloarthritis for more information.
The lower back is typically the main site of inflammation
In AS, the ligaments of the lower spine become inflamed at the points where they attach to the spinal bones (vertebrae). This gradually encourages the bone-making cells to grow bone within the ligaments. In time, these bony growths may become larger and form bony bridges between vertebrae that are next to each other. Eventually this can fuse some of the vertebrae together so they form one larger bone.
The sacroiliac joints and their nearby ligaments are also commonly affected. This inflammation too can ultimately end in fusion between the sacrum and pelvis.
Other areas of the body may be affected
The disease is not always confined to the spine and sacroiliac joints. In some cases, inflammation occurs in other joints and in other parts of the body outside of the spine (detailed below).
Understanding the lower back
The spine is made up of lots of bones stacked on top of each other. Each bone (vertebra) is the shape of a squat cylinder and between each vertebra is a disc. The discs are made of rubber-like substance which allows the spine to be fairly flexible. Strong ligaments attach the spinal bones (vertebrae) to each other and make the spine strong. At the bottom of the spine five vertebrae are fused together. They form a triangular-shaped bone called the sacrum. There are two large joints on either side of the bottom of the spine that join it on to the pelvis. They are called the sacroiliac joints because they join the sacrum (sacro-) to the main bone of the pelvis which is called the ilium (-iliac).
Who gets ankylosing spondylitis?
AS most commonly begins between 20 and 30 years of age, but can occasionally first develop in children and older adults. It is twice as common in men as it is in women. There may be a family history with two or more members of a family being affected. About 1 in 1,000 people in the UK develop AS.
What causes ankylosing spondylitis?
The cause is not known. However, there is a strong hereditary (genetic) tendency. For example, there is a strong association with a gene called HLA-B27. About 9 out of every 10 people with AS have this gene compared with fewer than 1 out of every 10 in the general population. However, having this gene does not mean that you will automatically develop AS. Most people with this gene do not develop AS. Also, some people develop AS who do not have this gene. It is thought that something may trigger AS to develop in people who have an inherited tendency to develop AS, and the gene HLA-B27 provides a strong tendency. As yet, the trigger is not known and other genes and factors may also be involved in causing AS.
Symptoms of ankylosing spondylitis
The most common symptoms of AS are back pain and stiffness.
Back pain is the main symptom. The pain usually starts in the lower back. You may think of it as just mild backache at first. It typically becomes gradually worse over several months. You may have pain over your buttocks and down the back of your thighs. The buttock pain may be felt sometimes on one side and sometimes on the other side. Coughing or straining may make pain worse. Rest does not make it better. In fact, the pain may wake you from sleep. Instead, exercise and movement usually ease the pain. (This is the opposite to most bouts of common nonspecific lower back pain which may alert a doctor to the diagnosis of AS.) The pain tends to be worse first thing in the morning. Lying in bed after waking is often uncomfortable. The pain tends to ease as the day goes on.
The middle (chest part) of the spine may become affected. If this occurs, the joints between the ribs and the spine may also become painful.
Stiffness in the lower spine
The stiffness can be quite severe first thing each morning. It usually improves with activity and exercise, and tends to ease as the morning goes on.
Other joint symptoms apart from the spine
Other joints are affected at some stage in about 4 out of every 10 people with AS. The most common are the hips, knees, ankles and shoulders. Affected joints can become painful, stiff and swollen.
Inflammation of tendons and ligaments
Tendons and ligaments in various parts of the body (in addition to those attached to the vertebrae of the lower spine) may become inflamed and painful where they attach to bones. Common examples are the Achilles tendon (Achilles tendinopathy) where the calf muscles attach to the heel, and where chest muscles attach to the ribs (costochondritis).
Inflammation of part of the eye (uveitis)
Uveitis is an inflammation of the eye. It affects about 1 in every 3 people with AS from time to time. Tell a doctor urgently if you have AS and develop a painful or red eye. If you develop uveitis, treatment with eye drops should be started as soon as possible after eye symptoms begin. Treatment of uveitis is usually successful. However, if not treated quickly there can be permanent loss of vision in the eye (partial or complete).
Some people with AS feel generally unwell with symptoms of tiredness or depression. Unintended weight loss or anaemia sometimes occurs.
Some other conditions develop more commonly than would be expected in people who have AS. For example, people with AS have a greater than average chance of developing:
- Ulcerative colitis.
- Crohn's disease.
- 'Thinning' of the bones (osteoporosis).
- Lung fibrosis.
- Cardiovascular disease (see later).
- Heart valve problems.
Note: most people with AS do not get these conditions - it is just that they are more common in people with AS than would be expected in the general population.
How is ankylosing spondylitis diagnosed?
This condition is diagnosed from your symptoms and X-ray or magnetic resonance imaging (MRI) pictures. Blood tests can be helpful, but mainly to rule out other conditions.
As the disease progresses, typical changes develop on X-ray pictures of the sacroiliac joints and spine. The X-ray pictures show the bones (vertebrae) gradually fusing together. However, these changes may take several years to become bad enough to be seen on X-ray pictures.
Until recently, the X-ray changes were the only way to confidently confirm AS. More recently, an MRI scan of the sacroiliac joints has been used to confirm the diagnosis at an earlier stage. An MRI scan can give a much more detailed view of a joint than a traditional X-ray picture and can detect inflammation in the sacroiliac joints.
How does ankylosing spondylitis progress?
Symptoms can vary in severity and usually wax and wane. Flare-ups of inflammation which cause periods of worse pain and stiffness tend to occur from time to time. If joints outside your spine are affected, they tend to flare up at the same time as back symptoms. The number of flare-ups that occur, how severe they are, and how long they last, can vary greatly from person to person.
In time, the movement and flexibility of your spine may reduce. This happens as the inflammation and bony growths cause gradual joining together (fusion, or ankylosis) of some of your bones. The number of vertebrae involved and how much fusion happens vary from person to person. A bent-over (stooping) posture may develop if it is very severe.
Ankylosing spondylitis treatment
The aims of treatment are:
- To ease pain and stiffness.
- To keep your spine as mobile and flexible as possible.
- To slow down the progress of the disease.
Physiotherapy and exercise
It is vital to have as good a posture as possible and a regular exercise routine. This helps you to keep a full range of spinal movement and may help to prevent your condition worsening. Regular specific exercises are thought to limit the extent of any spinal deformity that may develop. The exercises may also ease back pain. You will normally be referred to a physiotherapist who will advise on the exact exercises to do. Doing exercises in a group may be particularly beneficial. Exercises should become a routine part of life. Ideally, they should be done daily.
These medicines are also called non-steroidal anti-inflammatory drugs (NSAIDs). An important reason to take these medicines is to ease pain so that you can do regular exercises without much discomfort.
It is thought that anti-inflammatory medicines may not only ease symptoms of AS but may also slow down the progression of AS. Therefore, advice is to take them regularly, not just as and when the pain flares up. There are several different anti-inflammatory medicines - for example, ibuprofen, diclofenac and naproxen - but there are many others. If one does not suit, another may be fine.
However NSAIDs can have side-effects and not everyone can take them. For example:
- Stomach pain and bleeding from the stomach are the most serious. The risk of this is higher if you are aged over 65 years, or have had a duodenal or stomach ulcer. In some situations, your doctor may prescribe another medicine to protect the stomach from these possible problems. Note: stop taking the tablets and see a doctor urgently if you develop any of the following whilst taking anti-inflammatory medicines:
- Stomach (abdominal) pains.
- Passing blood or black stools (faeces).
- Bringing up (vomiting) blood.
- You may not be able to take anti-inflammatory medicines if you have asthma, high blood pressure, chronic kidney disease, or heart failure.
The leaflet which comes with the tablets gives a full list of possible side-effects.
It is not known whether different NSAIDs are better than others in improving AS.
Painkillers such as paracetamol may be sufficient if symptoms are mild between flare-ups and you can't take an anti-inflammatory painkiller. You can also take paracetamol in addition to an anti-inflammatory medicine for top-up pain relief.
Newer powerful medicines that suppress the immune system have become available in recent years. They lessen the damaging effect of AS on the joints. They tend to be divided into two groups: biological therapies and immunomodulators. Immunomodulators are useful in rheumatoid arthritis but research suggests they are not very effective in AS. However biological medicines (also called biologics), have made a signficant impact on the treatment of AS.
Biological medicines are substances made by living organisms such as cloned white blood cells. In other words they have been genetically engineered. They are designed to target specific molecules of the immune system involved in inflammation. In AS, a chemical called cytokine tumour necrosis factor alpha (TNF-alpha) is involved in causing inflammation. Certain medicines in a group called TNF-alpha inhibitors block the action of this chemical. As a result they reduce inflammation and prevent damage to the joints. TNF-alpha inhibitors are also sometimes called anti-TNF-alpha drugs.
TNF-alpha inhibitors are now recommended to people with severe AS who have not responded well enough to NSAIDs or who can't take them. There are several TNF-alpha inhibitors available:
- Certolizumab pegol
They cannot be taken as tablets or liquids to swallow as they would be destroyed in the stomach, so they are given as an injection under the skin (except for infliximab which has to be given in a drip). You can learn how to do this yourself or a nurse will do it for you. How often they are given depends on the medicine you have been prescribed - it can vary from twice a week to once every eight weeks.
There are risks associated with taking these medicines and they require special monitoring, as some people develop serious side-effects. For example, taking these medicines may make you more prone to developing a serious infection (including tuberculosis, sepsis and pneumonia). Rarely, they may also increase the chance of you developing some types of cancer, including lymphoma and leukaemia. However, all these conditions seem to be much more rare than was initially thought.
It is not known if any of the TNF-alpha inhibitors are more effective or safer than the others.
In the UK the National Institute for Health and Care Excellence (NICE) recommends that treatment with a TNF-alpha inhibitor should only be started and supervised by a specialist who is experienced in diagnosing and treating AS. After 12 weeks, treatment should continue only if your AS has shown an adequate improvement. Improvement is often measured by a test called the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI). This asks you various questions:
- How tired are you?
- How much pain do you have in your back?
- How stiff are you in the morning?
- How long does your stiffness last?
- Do you have any areas of tenderness?
- How bad is any joint pain or swelling (other than your back or neck)?
If the improvement is not maintained or if the medicine stops working then treatment should be stopped. Other medicines, such as secukinumab or ixekizumab, may be tried if TNF-alpha inhibitors can't be used or are ineffective.
Occasionally, other medicines are used:
- A steroid injected directly into a badly inflamed joint is sometimes used to ease symptoms. Steroids taken as tablets or liquids are not used in AS.
- Medicines called bisphosphonates are used to treat osteoporosis that is associated with AS.
Other treatments sometimes used include the following:
- Transcutaneous electrical nerve stimulation (TENS) machines are sometimes used to ease pain. (These give tiny electrical currents into the affected area.)
- Heat - for example, a hot shower - may help to ease pain, particularly each morning.
- Some people find regular massage is soothing.
- Surgery may be needed:
- A hip replacement, as the hip sometimes becomes badly damaged by AS.
- Surgery for severe spinal deformity.
Ankylosing spondylitis and cardiovascular disease
If you have AS, you have an increased risk of developing cardiovascular disease when you get older. Cardiovascular disease is disease of the heart and blood vessels, caused by a fatty substance called atheroma. This may eventually lead to conditions such as angina, heart attack or stroke. It is not clear why the risk is increased in people with AS. It may be that the persistent (chronic) inflammation of the condition is partially responsible. There is some evidence that TNF-alpha inhibitors might reduce the risk of developing cardiovascular disease but further research is needed to confirm this.
You should consider doing everything you can to reduce the risk of cardiovascular disease by other means.
For example, if possible:
- Do not smoke.
- Eat a healthy diet such as the Mediterranean DIet.
- Exercise regularly.
- Lose weight if you are overweight.
- If you have high blood pressure, diabetes, or a high cholesterol level, make sure they are well controlled on treatment.
What is the outlook?
There is no cure for AS and the outlook (prognosis) tends to be variable. The pattern of symptoms within the first 10 years of disease often suggests the likely long-term degree of disability. In one study, about 7 out of 10 patients with mild spinal restriction after 10 years did not progress to severe spinal involvement. However, among patients who developed long-term severe spinal involvement, 8 out of 10 had severe spinal restriction within 10 years.
A small proportion of patients with chronic progressive disease develop significant disability due to spinal fusion. About 1 out of every 10 people with AS have a severe form of the disease and may become quite disabled over time. However, the recent introduction of treatment with TNF-alpha antagonists (described above) seems to have improved the outlook for people with more severe AS.
In most cases, episodes of arthritis outside the spine and/or eye inflammation do not occur, or only occur now and again. In a small number of cases, these problems outside the spine return (recur) frequently, or become severe. Eye inflammation (uveitis) may lead to severe sight impairment if not treated promptly.
People with established AS have an increased risk of fracturing the spine if they are involved in an accident such as a car crash or if they fall. This is because the spine becomes easier to fracture as it becomes more stiff and rigid. It is also due to osteoporosis which is more common in people with AS.
Further reading and references
Spondyloarthritis in over 16s: diagnosis and management; NICE Guidance (Feb 2017)
BSR and BHPR guideline for the treatment of axial spondyloarthritis (including ankylosing spondylitis) with biologics; British Society for Rheumatology (2016)
Kroon FP, van der Burg LR, Ramiro S, et al; Nonsteroidal Antiinflammatory Drugs for Axial Spondyloarthritis: A Cochrane Review. J Rheumatol. 2016 Mar43(3):607-17. doi: 10.3899/jrheum.150721. Epub 2016 Feb 1.
TNF-alpha inhibitors for ankylosing spondylitis and non-radiographic axial spondyloarthritis; NICE Technology Appraisal Guidance, February 2016
Secukinumab for active ankylosing spondylitis after treatment with non-steroidal anti-inflammatory drugs or TNF-alpha inhibitors; NICE Technology appraisal guidance, September 2016
Ixekizumab for treating axial spondyloarthritis; NICE Technology appraisal guidance, July 2021
Ankylosing spondylitis; NICE CKS, May 2019 (UK access only)