Ankylosing spondylitis (axial SpA) explained

What ankylosing spondylitis is

Ankylosing spondylitis is a long-term inflammatory condition in which the body's immune system causes inflammation mainly in the spine and the joints that connect the spine to the pelvis, called the sacroiliac joints. Over time this inflammation can lead to pain, stiffness and, in some people, new bone forming across the joints, which can gradually reduce the flexibility of the spine. It is part of a family of conditions known as axial spondyloarthritis, where the word axial refers to the spine. Some people have clear changes visible on X-rays, while others have inflammation that shows only on more detailed scans; both are part of the same spectrum. It tends to run in families and is linked to a gene called HLA-B27, though many people who carry this gene never develop the condition.

Recognising inflammatory back pain

The key to spotting ankylosing spondylitis is recognising a particular pattern of back pain that differs from ordinary mechanical back strain. Inflammatory back pain usually starts gradually before the age of about 45, often in the late teens or twenties. Unlike everyday back pain, it tends to be worse with rest and better with movement and exercise, and it often causes prolonged stiffness in the morning lasting more than half an hour. People may wake in the second half of the night with pain, and buttock pain that alternates from side to side is common. The pain and stiffness usually improve as the day and activity go on. When back pain in a young adult shows this inflammatory pattern and lasts more than three months, it should prompt assessment for spondyloarthritis rather than being dismissed as a simple strain.

Beyond the back

Although the spine is the main target, ankylosing spondylitis can affect other parts of the body. Some people develop pain and swelling in joints such as the hips, knees or shoulders, and inflammation where tendons attach to bone, for example causing heel pain. A particularly important feature is inflammation inside the eye, called uveitis or iritis, which causes a painful, red eye with blurred vision and sensitivity to light and needs prompt eye assessment to protect sight. The condition is also linked with the skin condition psoriasis and with inflammatory bowel conditions such as Crohn's disease and ulcerative colitis. Fatigue is common and can be one of the most troublesome symptoms. Because it can affect several systems, care sometimes involves more than one specialist working together.

How it is diagnosed

Diagnosis is often delayed, so awareness matters. A rheumatologist puts together the picture from the history of inflammatory back pain, a physical examination of spinal movement and other joints, and tests. Blood tests may show signs of inflammation and can check for the HLA-B27 gene, though this gene alone neither confirms nor rules out the condition. Imaging is central: X-rays can show established changes in the sacroiliac joints, but MRI scans are more sensitive and can reveal active inflammation early, before X-ray changes appear. This is important because it allows earlier diagnosis of people whose X-rays still look normal. Because ordinary back pain is so common, anyone with a long history of inflammatory-pattern back pain starting young should be referred to rheumatology for proper assessment rather than continuing to be treated as simple back pain.

Treatment and staying active

There is no cure, but treatment is effective and the outlook has improved greatly. The foundation of management is regular exercise and physiotherapy to keep the spine mobile, maintain good posture and reduce stiffness — staying active is genuinely one of the most powerful treatments. Anti-inflammatory medicines help control pain and stiffness for many people. When these are not enough, modern medicines called biologics, which target the specific parts of the immune system driving the inflammation, can dramatically improve symptoms and quality of life. Not smoking is especially important, as smoking worsens the condition. People should also know the signs of eye inflammation and seek urgent eye care if they develop a painful red eye. With early diagnosis, regular exercise and modern treatment, most people can control symptoms well and stay active and independent.