Ankylosing spondylitis

Ankylosing spondylitis is a form of arthritis that usually develops in teenagers and young adults. It causes pain and stiffness in the back and other joints.

By Wallace Health I Medically reviewed by Adrian Roberts.
Page last reviewed: October 2018 I Next review due: October 2023

What is ankylosing spondylitis?

Ankylosing spondylitis is a chronic (long-term) condition that causes inflammation of your spine and other joints. Symptoms include joint pain, stiffness and swelling. It's a form of arthritis, but unlike osteoarthritis or spondylosis, which are caused by wear and tear as we age, ankylosing spondylitis usually first develops in teenagers and young adults. It affects about one in 1,000 people in the UK and can run in families. 

Ankylosing means fusing together, while spondylitis refers to inflammation of the spine. In ankylosing spondylitis, your back, neck, hips or knees may slowly become less flexible. In severe cases, inflammation of the ligaments attached to the lower bones of your back can cause bone-making cells to produce bone inside these ligaments. This causes the bones in your lower back to fuse together and can eventually cause these bones to fuse with your pelvis. Ankylosing spondylitis can sometimes affect other joints and areas of the body, including your hips, knees, ankles, shoulders, heels and ribs. 

Understanding the lower back

Ankylosing spondylitis mainly affects the spine. Your spine is made of a series of bones stacked on top of each other (vertebrae). In between each vertebra are rubber-like cushions called intervertebral discs, which allow your spine to be flexible. Ligaments connect your spinal bones to each other to make your spine strong. 

The bottom of your spine has five vertebrae that are naturally fused together to form a triangular-shaped bone called the sacrum. The sacrum forms part of two large joints which connect it to the pelvis, specifically to a bone in the pelvis called the ilium. These two large joints are called sacroiliac joints.

How to tell if you have ankylosing spondylitis

The most common symptoms are pain and stiffness in your lower back and buttocks, which usually develop between ages 20–30. You might also notice pain or swelling in your joints, including your knees and hips — this occurs in 4 out of 10 people with ankylosing spondylitis.

Other symptoms can include:

  • Anaemia
  • Arthritis — inflammation of joints, such as your hips or knees, causing swelling and warmth around the affected joints, pain on moving these joints and tenderness when examined 
  • Back pain, chest pain, pain in your heels, shins and/or around your buttocks
  • Enthesitis — painful inflammation at points where a tendon or ligament attaches to a bone, commonly affecting the top of your shin bone, behind and/or under your heel, and where your ribs attach to your breast bone, which may cause chest pain or difficulty breathing deeply 
  • Fatigue (extreme tiredness) — this commonly occurs when ankylosing spondylitis is left untreated
  • Feeling generally unwell and/or depressed

You may also unintentionally lose weight. You may find that your symptoms improve with exercise but are worse:

  • After resting or sitting
  • At night, which can cause you to wake up regularly due to the pain
  • On waking up

Symptoms usually develop gradually over months or years and can come and go. For some people, symptoms worsen over time, while for others symptoms improve. 

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Diagnosis and tests for ankylosing spondylitis

See your GP if you have pain, stiffness or swelling in your joints that:

  • Has lasted for three months or more
  • Improves with exercise, but not with rest 
  • Is affecting your sleep

Your GP may refer you to a rheumatologist (specialist in muscles and joints).

Getting an accurate diagnosis for ankylosing spondylitis can take time as it can develop slowly and there’s no single test for it. Your doctor will assess your symptoms and may arrange further investigations to check for inflammation of your spine and joints, such as:

They may also carry out a blood test to detect a specific gene that most people with ankylosing spondylitis carry. However, this test is not completely reliable as some people with ankylosing spondylitis do not carry this gene, while others who do carry this gene may not develop ankylosing spondylitis.

Confirming ankylosing spondylitis

It can take years to confirm a diagnosis of ankylosing spondylitis. This is because X-ray and MRI scans cannot always detect inflammation and fusing of your spine in the early stages of the condition.  

A diagnosis can usually be confirmed when an X-ray or MRI scan shows inflammation of your sacroiliac joints (sacroiliitis) and you have one or more of the below symptoms:

  • Lower back pain for three months or more, which improves with exercise and stays the same or worsens with rest
  • Restricted movement of your lower back 
  • Restricted chest expansion when you breathe deeply compared with what is normal for your age and sex 

If you have all of the above symptoms but sacroiliitis cannot be detected, or you do not have any of these symptoms but sacroiliitis is detected, your doctor will give you a diagnosis of probable ankylosing spondylitis.

Causes of ankylosing spondylitis

The cause of ankylosing spondylitis isn't known, but these factors may increase your risk:

  • Age — ankylosing spondylitis usually begins in the late teens or early 20s
  • Family history — if your parent, brother or sister have or had ankylosing spondylitis, you're around three times more likely to develop it than if no family member has it
  • Gender — ankylosing spondylitis is three times more common in men than women
  • Genetic — more than 9 in 10 people with ankylosing spondylitis carry a gene called HLA-B27, which doesn't directly cause the condition but makes you more likely to develop it, eg in response to an environmental factor that can trigger the condition

In the general population, about eight in every 100 people have the HLA-B27 gene but the majority will not develop ankylosing spondylitis.

Can ankylosing spondylitis be inherited?

Ankylosing spondylitis can run in families and the HLA-B27 gene is a risk factor for the condition. If you carry this gene and have ankylosing spondylitis, there is a one in two chance that the gene will be passed onto your children. For children carrying this gene, 5–20% will develop the condition.

Common treatments for ankylosing spondylitis

Ankylosing spondylitis cannot be cured and the damage caused cannot be reversed. However, there are treatments that can make a difference by easing your pain and stiffness, keeping your spine as flexible as possible, and slowing down the progression of the condition. 

Regular exercise and physiotherapy are important to improve your posture and the mobility of your spine — this will help prevent your spine from becoming more stiff and painful. Physiotherapy can involve group or individual exercise programs, massage and hydrotherapy. Playing sport and swimming can ease your symptoms too. 

Medicines can also help treat flare-ups, including: 

  • Corticosteroid injections — these injections are given up to three times per year and include side effects such as infections and problems around the injection site, including skin colour changes, tissue wasting and tendons bursting
  • DMARDs (disease-modifying anti-rheumatic drugs), such as sulfasalazine — these drugs are mainly used to treat pain and inflammation outside of the spine
  • Painkillers
  • NSAIDs (non-steroidal anti-inflammatory drugs), such as ibuprofen, naproxen, diclofenac and etoricoxib
  • Anti-TNF (tumour necrosis factor) injections — your doctor may recommend these injections if you have severe ankylosing spondylitis and are not responding well to NSAIDs or cannot take them 
  • Secukinumab — your doctor may recommend this antibody treatment if you are not responding to NSAIDs or anti-TNF injections

Anti-TNF injections and secukinumab are biological medicines as they are not manufactured artificially but are made by living organisms. 

The long-term effects of anti-TNF injections are currently unknown, which is why you will need to be carefully monitored if you have these injections. Side effects include becoming more likely to develop a serious infection, such as pneumonia, sepsis or tuberculosis. In very rare cases your risk of developing certain cancers, such as leukaemia and lymphoma, may increase. 

Your doctor will usually prescribe anti-TNF injections for 12 weeks, after which they will review your condition. Only if this treatment has shown significant improvement in your condition will your doctor recommend you continue with it. 

Other treatments for ankylosing spondylitis depend on the severity of the condition and the affected joints, and might include:

  • Corrective surgery of the spine — this surgery is carried out in rare cases where the spine has become severely bent 
  • Joint replacement surgery, such as hip replacement or knee replacement — this surgery is only carried out if the affected joint is severely damaged
  • Physiotherapy — this involves physical manipulations and massage to improve the flexibility of your spine

Whichever treatment your doctor recommends, you will need regular check-ups to see how your condition is progressing and if the treatment is working.

Complications of ankylosing spondylitis

For some people with ankylosing spondylitis, their condition improves over time, while for others it worsens. The severity of the symptoms also varies considerably from one person to the next. Some people can remain independent or have minor disabilities, while others become severely disabled due to joint damage and their spine fusing, which causes reduced mobility. 

Life expectancy is not affected by the condition but ankylosing spondylitis can increase your risk of developing other life-threatening diseases, such as: 

  • Amyloidosis, the build-up of a protein called amyloid in organs such as your heart, kidneys and liver, which causes symptoms including fatigue, fluid retention (oedema), shortness of breath, tingling or numbness in your hands and feet, and weight loss — this is a very rare complication of ankylosing spondylitis
  • Cardiovascular disease, which affects the heart and/or blood vessels and can lead to angina, heart attack or stroke — your risk of developing this disease can be reduced through lifestyle changes, such as eating a healthy diet, losing weight, regular exercise and stopping smoking  
  • Chest infections
  • Kidney disease 
  • Osteoporosis — this causes your bones to become weaker, which makes fractures and breaks more likely after minor injuries or falls 
  • Spinal fractures

Ankylosing spondylitis can also increase your risk of developing other conditions that can affect your quality of life, including: 

  • Cauda equina syndrome, compression of the nerves at the bottom of your spine, which causes symptoms including bowel or urinary incontinence, pain or numbness in your lower back and buttocks, and weakness in your legs — this is a very rare complication of ankylosing spondylitis
  • Iritis, swelling and redness of the front part of the eyes, usually limited to one eye, which causes symptoms including eye pain, blurry or cloudy vision, and sensitivity to light — this can be treated with corticosteroid eye drops
  • Joint damage — in severe cases joint replacement surgery may be needed

Frequently asked questions

What is the main cause of ankylosing spondylitis?

The cause of ankylosing spondylitis isn't known, but there are factors that can increase your risk of developing it. It usually first develops in your late teens or early 20s and is three times more likely to affect men than women. It runs in families and there is a genetic risk factor — more than 9 in 10 people with ankylosing spondylitis carry a gene called HLA-B27. However, you can carry this gene and not develop the condition.

Is ankylosing spondylitis an autoimmune disease?

Yes, ankylosing spondylitis is an autoimmune disease — this refers to diseases where your body attacks its own healthy tissues. Ankylosing spondylitis is also an inflammatory disease as it causes inflammation of the spine and sometimes other joints in your body.

What does ankylosing spondylitis pain feel like?

Ankylosing spondylitis causes dull pain in and around your lower back and buttocks, as well as stiffness. Pain and stiffness can also occur in other joints in your body. Exercise improves the pain while rest either makes no difference or makes the pain worse.

What organs does ankylosing spondylitis affect?

Ankylosing spondylitis mainly affects the spine but can sometimes affect other joints in the body, such as your hips, knees, ankles, shoulders, heels and ribs. It can also increase your risk of developing other conditions that can affect your organs, such as your eyes, lungs, heart, kidneys and liver.

What foods to avoid with ankylosing spondylitis?

There is no dietary cure for ankylosing spondylitis but certain foods can worsen your inflammation and are best to avoid. These include foods:

High in sugar, such as sweets, fruit juices and sauces
High in salt and sodium, such as smoked, cured, preserved or tinned meat, and frozen ready-meals
High in saturated fat, such as cheese, full-fat dairy products, pizza, processed foods and red meat
High in omega-6 fatty acids, such as mayonnaise, pastries, processed foods, salad dressings and vegetable oils

What aggravates ankylosing spondylitis?

A lack of physical activity can aggravate your symptoms but doing too much can also strain your joints. It is important to strike a balance with your physical activity and know when to take a break. Poor posture can also worsen your symptoms by weakening your back muscles. Other factors that can aggravate ankylosing spondylitis include:

Being overweight
Lack of sleep
Not taking your medication as prescribed, eg skipping doses