Ankylosing spondylitis.
Ankylosing spondylitis (AS) is a chronic inflammatory disease that primarily affects the spine and sacroiliac joints, but it's systemic — affecting eyes, gut, skin, and cardiovascular system too. It's strongly associated with the HLA-B27 gene and driven by the IL-23/IL-17 cytokine pathway. Modern biologics (TNF and IL-17 inhibitors) prevent the spinal fusion that used to be common. Exercise is foundational — it's not optional, and it's not dangerous. Daily movement preserves mobility.
The mechanism, why AS stays inflamed.
AS belongs to a family of inflammatory diseases called spondyloarthropathies. Four mechanisms keep the inflammation running:
HLA-B27 association
Over 90% of AS patients carry the HLA-B27 gene. This doesn't mean HLA-B27 causes AS — most people with HLA-B27 never develop it — but it's the strongest genetic association in autoimmune disease.
IL-23 / IL-17 axis
The driving cytokine pathway is IL-23/IL-17, not TNF alone. This is why IL-17 blockers (secukinumab, ixekizumab) work so well in AS, and why some treatments effective in RA fail here.
Enthesitis at sacroiliac joints
Inflammation at the entheses (tendon insertions into bone) — especially at the sacroiliac joints — is the hallmark. This pattern of inflammation causes new bone formation, leading to spinal fusion if untreated.
Gut-spine axis
Up to 60% of AS patients have subclinical gut inflammation. The same IL-23/IL-17 pathway driving the spine also drives inflammatory bowel disease. This is why AS and IBD cluster.
The 4-step plan, applied to AS.
Get the right diagnosis
Inflammatory back pain pattern (worse with rest, better with movement, morning stiffness >1 hour, age of onset <45), MRI of sacroiliac joints to detect active inflammation before X-ray changes appear, HLA-B27 testing, ESR/CRP. The ASAS criteria are the modern standard. Early treatment prevents fusion.
Learn more about labs →Clean up your food
Mediterranean-style eating reduces inflammation. Some patients with concurrent IBD benefit from low-FODMAP or specific carbohydrate diet trials. Watch for gut symptoms — they're more common in AS than most patients realize.
AS & diet →Detox your daily life
Smoking is one of the strongest modifiable risk factors — it accelerates spinal fusion, raises CV risk (already elevated in AS), and reduces biologic response. Quitting is non-negotiable.
AS & environment →Build a stronger body
Exercise isn't optional in AS — it's foundational treatment. Daily mobility work, Pilates, yoga, swimming, posture-focused movement. Resistance training improves outcomes. Patients who stop moving are the ones who fuse.
AS & exercise →
Go deeper.
Common misconceptions.
"AS is just bad back pain."
AS is a systemic inflammatory disease. It affects eyes (uveitis in 30–40%), gut (subclinical IBD common), skin (psoriasis overlap), cardiovascular system, and lungs. Treating it as "just" back pain misses the systemic risks.
"Exercise is dangerous with AS."
Exercise has the strongest evidence base of any non-medication intervention in AS. Daily mobility work is what preserves function. Patients who stop moving are the ones who fuse. The pattern to avoid is bed rest — not movement.
"My spine will inevitably fuse."
With modern treat-to-target therapy (biologics) plus daily exercise, most patients prevent the spinal fusion that defined AS in older textbooks. The bamboo-spine images you see in classical AS describe pre-biologic-era patients, not the current standard of care.
When to see a rheumatologist.
See a rheumatologist if you have:
- Back pain that started before age 45 and has lasted more than 3 months
- Morning stiffness in the back or hips lasting more than 1 hour
- Back pain that improves with movement and worsens with rest (especially in the second half of the night)
- A history of uveitis or iritis plus back pain
- Psoriasis or inflammatory bowel disease plus back pain
- Family history of AS plus suggestive symptoms
- Heel pain (Achilles or plantar fascia) that doesn't resolve
The average delay from symptom onset to diagnosis in AS is 7–10 years — far too long. If your back pain has the inflammatory pattern above, push for a rheumatology referral and MRI of the sacroiliac joints.
- Sieper J, Poddubnyy D. Axial spondyloarthritis. Lancet, 2017. PubMed 28290320
- Rudwaleit M, et al. The development of ASAS classification criteria for axial spondyloarthritis. Ann Rheum Dis, 2009. PubMed 19297344
- Ward MM, et al. 2019 ACR/SAA/SPARTAN recommendations for AS treatment. Arthritis Care Res. PubMed
- Exercise therapy in AS: systematic review. Cochrane Database Syst Rev. PubMed