Ankylosing Spondylitis

What happens in ankylosing spondylitis

AS is part of a family of conditions called spondyloarthritis. Inflammation begins where ligaments and tendons attach to bone (the entheses), particularly in the sacroiliac joints and spine. Over time, the body responds by forming new bone, which can bridge vertebrae and stiffen the spine. In advanced cases, the spine can fuse into a rigid "bamboo spine" and lose its normal curves, causing a stooped posture.

When inflammation is visible on MRI but X-rays are still normal, it is called non-radiographic axial spondyloarthritis. Both are treated similarly.

Symptoms

Inflammatory back pain

The key early symptom is chronic low back and buttock pain with these features:

• starts gradually before age 45
• lasts more than 3 months
• morning stiffness lasting more than 30 minutes
• improves with exercise, not with rest
• wakes you in the second half of the night
• pain in the buttocks that may alternate sides

This pattern contrasts with common mechanical back pain, which usually gets worse with activity and better with rest.

Other symptoms

• Reduced spinal movement and posture changes over years
• Enthesitis: heel pain (Achilles tendon or plantar fascia), chest wall pain
• Peripheral arthritis: swollen hips, knees or ankles
• Fatigue
• Dactylitis: swollen "sausage" fingers or toes

Conditions linked with AS

• Uveitis: a painful, red, light-sensitive eye affects up to about a third of people with AS at some point.
• Inflammatory bowel disease: Crohn's disease or ulcerative colitis.
• Psoriasis.
• Osteoporosis and spinal fractures.
• Heart and lung involvement: rarely, aortic valve problems, heart rhythm problems, and reduced chest expansion.

Causes and risk factors

The cause is not fully understood. Genetics plays a major role:

• HLA-B27: most people with AS carry this gene, but most people with HLA-B27 never develop AS.
• Family history: having a parent or sibling with AS raises risk.
• Gut inflammation and immune pathways involving IL-17 and TNF are central.

Diagnosis

Diagnosis is often delayed by several years because back pain is so common. A rheumatologist uses:

1. History and examination: the pattern of back pain, spinal flexibility (Schober test), chest expansion, and checking for enthesitis and arthritis.
2. Blood tests: HLA-B27, and inflammatory markers CRP and ESR (which can be normal).
3. Imaging: X-rays of the sacroiliac joints show damage in established disease. MRI detects early inflammation before X-ray changes.

Treatment

Exercise and physical therapy

Daily exercise is a core treatment. Stretching, posture exercises, deep breathing, swimming and strengthening maintain flexibility and reduce pain and stiffness. A physical therapist can design a program.

Medicines

• NSAIDs (such as naproxen, ibuprofen, celecoxib) are first-line and very effective for many people. Use under medical supervision because of stomach, kidney and heart risks.
• Biologics: TNF inhibitors (adalimumab, etanercept, infliximab, certolizumab, golimumab) and IL-17 inhibitors (secukinumab, ixekizumab, bimekizumab) for active disease despite NSAIDs.
• JAK inhibitors (tofacitinib, upadacitinib) are another option.
• Sulfasalazine or methotrexate may help peripheral joint arthritis but do not help spinal disease.
• Steroid injections for individual inflamed joints or entheses. Long-term oral steroids are not recommended.

Surgery

Hip replacement for severe hip damage, and rarely spinal surgery for severe deformity or fractures.

Living with ankylosing spondylitis

• Do not smoke. Smoking is linked to more severe disease and faster progression.
• Keep active every day and maintain good posture, including a firm mattress and a thin pillow.
• Treat new spinal pain after a fall seriously, since a fused spine fractures more easily.
• Have regular eye checks if you notice redness or pain, and report symptoms promptly.
• Monitor bone density.

Most people with AS continue to work and live full lives, especially with modern treatments.

Frequently asked questions

What are the early signs of ankylosing spondylitis?

Early signs include low back and buttock pain that starts gradually before age 45, lasts more than 3 months, is worse in the morning and at night, and improves with exercise. Heel pain, a red painful eye or swollen joints may also occur.

Is ankylosing spondylitis an autoimmune disease?

It is an immune-mediated inflammatory disease, closely linked to the HLA-B27 gene and the IL-17 and TNF pathways. Unlike classic autoimmune diseases, it does not involve specific autoantibodies such as rheumatoid factor.

Does ankylosing spondylitis always cause the spine to fuse?

No. Many people never develop significant fusion, especially with early diagnosis, regular exercise, not smoking and effective treatment. Progression varies widely between individuals.

Can women get ankylosing spondylitis?

Yes. It is diagnosed more often in men, but women are commonly affected, particularly with non-radiographic disease, and are often diagnosed later. Symptoms may be more widespread in women.

Is HLA-B27 positive the same as having ankylosing spondylitis?

No. HLA-B27 is common in the general population, and most people who carry it never develop AS. A positive result supports the diagnosis only when symptoms and imaging also fit.