Hurtl
Ankylosing Spondylitis vs Axial Spondyloarthritis: What's the Difference?
By Tom, founder of Hurtl.
If you have just received a diagnosis, or are waiting for one, you may see ankylosing spondylitis (AS) and axial spondyloarthritis (axSpA) used in the same conversation and wonder whether they mean the same thing.
The short answer: ankylosing spondylitis is part of axial spondyloarthritis, but not everyone with axial spondyloarthritis has ankylosing spondylitis.
What is axial spondyloarthritis?
Axial spondyloarthritis (axSpA) is an inflammatory form of arthritis that mainly affects the spine and the sacroiliac (SI) joints, where the spine meets the pelvis.
Common symptoms include:
- Chronic back pain, often inflammatory in nature (pain that improves with movement rather than rest)
- Morning stiffness that can last 30 minutes or longer
- Fatigue
- Pain or stiffness in the buttocks, hips or chest
axSpA is an umbrella term. It includes people whose inflammation is visible on X-ray and people whose symptoms are present but X-rays look normal: a subtype called non-radiographic axial spondyloarthritis (nr-axSpA).
What is ankylosing spondylitis?
Ankylosing spondylitis (AS) is a subtype of axial spondyloarthritis. Historically it was the name used when sacroiliac joint damage was visible on plain X-rays.
In AS, inflammation in the spine and SI joints can lead to structural changes over time. Not everyone progresses in the same way, but the label usually reflects that radiographic (X-ray) damage is present.
You may still hear doctors or older articles use “ankylosing spondylitis” on its own. In modern classification, AS sits under the axSpA umbrella.
What is non-radiographic axial spondyloarthritis?
Non-radiographic axial spondyloarthritis (nr-axSpA) describes people who have clinical features of axSpA (inflammatory back pain, stiffness, fatigue and often a family or personal history of related conditions) but without the characteristic damage on standard X-rays.
That does not mean nothing is happening. MRI can often show inflammation in the SI joints or spine before X-ray changes appear. Many people with nr-axSpA have significant symptoms and benefit from the same specialist care as those with AS.
nr-axSpA can stay non-radiographic, or in some cases progress to radiographic axSpA (AS) over years. The label describes what imaging shows now, not a prediction of the future.
Comparison at a glance
| Axial SpA (axSpA) | Ankylosing spondylitis (AS) | |
|---|---|---|
| Back pain | Yes | Yes |
| Stiffness | Yes | Yes |
| Fatigue | Yes | Yes |
| X-ray changes in SI joints | Not always | Usually yes |
| Can progress over time | Yes | Yes |
| MRI may show inflammation | Often | Often |
AS is one form of axSpA. nr-axSpA is another. Same family of disease, different points on the imaging spectrum.
Why the terminology changed
For many years, ankylosing spondylitis was the label most people received. Research and imaging improved, and clinicians recognised a large group with the same inflammatory symptoms but normal X-rays, often after years of being told nothing was wrong.
The axSpA umbrella allows earlier, more accurate grouping: inflammatory back pain and related features matter, not only what a plain film shows. You may still see AS in letters, patient forums and older resources; axSpA is the broader, current framing in rheumatology.
Tracking symptoms with AS or axSpA
Whether your diagnosis is AS, nr-axSpA or still being clarified, symptom tracking can help in similar ways:
- Morning stiffness: duration and severity
- Pain: location, intensity and what helps
- Fatigue and sleep
- Flare triggers: stress, activity, illness
- Medication response: after starting or changing treatment
Patterns that are hard to remember week to week become visible over months. That supports better conversations with your rheumatology team and clearer questions about treatment.
If you want a dedicated tool for this, see our axial spondyloarthritis symptom tracker or our ankylosing spondylitis symptom tracker if you identify or search using the AS label — both support flare logging, charts and reports you can share at appointments. To understand the score your rheumatologist may use, read what is BASDAI and how it is calculated.