Ankylosing spondylitis (axial spondyloarthritis)

What axial SpA is

In axial SpA, the immune system causes inflammation in the joints of the spine and in the sacroiliac joints, where the spine meets the pelvis. Over time, in some people, this inflammation can lead to new bone forming, which makes parts of the spine stiff and less flexible.

The exact cause isn't known. It is strongly linked to a gene variant called HLA-B27. More than 8 in 10 people with AS carry it, but so do about 8 in every 100 people in the general population, most of whom never get the condition.

About 1 in 200 adults in the UK have axial SpA. Symptoms usually start in the late teens or twenties, and the average age they start is 26. It is often missed for years, because back pain is so common and there is no single test.

Types

Axial SpA is the umbrella name. Doctors split it into types depending on what shows on scans.

Symptoms and how it changes

Symptoms come on slowly, over months or years, and often come and go in flares. The typical pattern is called inflammatory back pain:

• back pain and stiffness that gets better with exercise but not with rest
• pain that is worse at night and early morning, and may wake you up
• stiffness in the morning that lasts more than 30 minutes
• pain in one or both buttocks, sometimes switching sides
• pain and swelling where tendons attach to bone, such as the heel, Achilles or chest
• pain and swelling in other joints, such as hips and knees
• extreme tiredness (fatigue)

1. Months to years

   Early symptoms

   Low back or buttock pain and morning stiffness, often in a young adult. Easy to mistake for ordinary back pain.

2. Days to weeks

   Flares

   Periods when pain, stiffness and tiredness get much worse. They may be set off by stress, illness or overdoing it, or come with no clear cause.

3. Ongoing

   Settled spells

   With treatment and exercise, many people have long periods when symptoms are well controlled.

4. Over many years

   Long term

   For some people symptoms ease. For others the spine slowly gets stiffer. Modern treatments and regular exercise help reduce this.

Everyone is different. Axial SpA does not usually affect life expectancy significantly.

When to get urgent help

Diagnosis and referral

There is no single test. Your GP will ask about your symptoms and may arrange blood tests for inflammation. Normal blood tests don't rule out axial SpA. A test for the HLA-B27 gene can help, but it isn't reliable on its own.

NICE says GPs should refer you to a rheumatologist if your back pain started before age 45, has lasted more than 3 months, and you have several other features. These include pain that wakes you in the second half of the night, buttock pain, pain that improves with movement, pain that eases within 48 hours of an anti-inflammatory, a close relative with axial SpA, psoriasis, inflammatory bowel disease or uveitis.

The rheumatologist may arrange X-rays or an MRI scan of your pelvis and spine. NICE says that if the X-ray doesn't show changes, you should be offered an MRI to look for early inflammation.

Treatments and medicines

Treatment aims to reduce pain, stiffness and tiredness, keep your spine moving, and protect it long term. Exercise is as important as medicine.

Biologic and targeted medicines

If NSAIDs haven't controlled your symptoms, your rheumatologist may offer a biologic or targeted medicine. These are usually considered after you have tried at least 2 NSAIDs, each for 2 to 4 weeks, and your disease is still active.

Most are injections you learn to give yourself at home. They are prescribed and supplied through your hospital team, not your GP or a pharmacy. They are continued only if they work well enough, usually judged by a fall in your symptom score and spinal pain. If one doesn't work, another can often be tried.

Surgery

Surgery is not often needed. The most common operation is a hip replacement when a hip has been badly damaged. Most people go home 1 to 3 days after a hip replacement, and many return to work after about 6 weeks, depending on their job. You should wait at least 6 weeks to drive. Rarely, surgery may be used to correct a severe forward curve of the spine.

Self-help and living well

Tips for getting the best treatment

Axial SpA and work

Axial SpA is likely to count as a disability under the Equality Act 2010 (the Disability Discrimination Act in Northern Ireland) if it has a substantial, more than minor, effect on your daily life and has lasted, or is likely to last, at least 12 months. Conditions that come and go in flares can count. The law looks at how you would be without treatment.

If it does, your employer must make reasonable adjustments. Examples include:

• A later start, as morning stiffness eases
• A sit-stand desk to change position often
• An ergonomic chair with good support
• A monitor arm or riser to keep your head up
• Regular breaks to stretch and move
• Working from home during flares
• Time off for infusions and appointments
• A workplace assessment

Access to Work is a government grant that can pay for equipment, travel to work and support. See GOV.UK on reasonable adjustments, or contact Acas or Citizens Advice for advice on your rights.

Benefits

If you can't work for a while, you may get Statutory Sick Pay from your employer for up to 28 weeks. If axial SpA affects daily tasks or getting around, you may be able to get Personal Independence Payment (Adult Disability Payment in Scotland), even if you are working. New Style ESA or Universal Credit may help if you can't work. Turn2us and Citizens Advice can help you check.

Support and sources

Last reviewed: October 2026.