If your letters say "axial spondyloarthritis" and your friends say "ankylosing spondylitis", nobody is wrong. The names describe the same spectrum from different angles, and the shift between them is recent enough that both are in everyday use.
The short version
Axial spondyloarthritis (axSpA) is the umbrella term for inflammatory arthritis that mainly affects the spine and sacroiliac joints. Ankylosing spondylitis (AS) is the form in which structural changes to the sacroiliac joints are visible on a plain X-ray — which is why it is also called radiographic axial spondyloarthritis (r-axSpA). When the same clinical picture is present but X-rays do not yet show those changes, the term is non-radiographic axial spondyloarthritis (nr-axSpA).
So: ankylosing spondylitis, also known as radiographic axial spondyloarthritis, is part of the axial spondyloarthritis spectrum. Every person with AS has axSpA; not everyone with axSpA has AS.
| Term | What it means | Imaging |
|---|---|---|
| Axial spondyloarthritis (axSpA) | The whole spectrum: inflammatory arthritis of the spine and sacroiliac joints | Either of the below |
| Radiographic axSpA (r-axSpA) = ankylosing spondylitis (AS) | axSpA with definite sacroiliac joint changes on X-ray | X-ray changes present |
| Non-radiographic axSpA (nr-axSpA) | axSpA with the clinical picture but without definite X-ray changes; inflammation may be visible on MRI | No definite X-ray changes; MRI may show inflammation |
Why the terminology changed
X-ray changes in the sacroiliac joints can take years to appear, and for a long time a diagnosis of AS depended on them. That left many people with clear symptoms and no name for their condition. Classification criteria published by ASAS in 2009 described the earlier stage in which inflammation is visible on MRI but not on X-ray and labelled it non-radiographic axial SpA, bringing both under the axSpA umbrella (Rheumatology, 2020).
The two forms carry a comparable burden of symptoms, and UK guidance treats the spectrum together: NICE’s guideline covers spondyloarthritis as a whole (NICE NG65), and its appraisal of TNF-alpha inhibitors covers both ankylosing spondylitis and non-radiographic axial spondyloarthritis (NICE TA383). Organisations have followed: the UK’s patient charity is now the National Axial Spondyloarthritis Society and writes "axial SpA (AS)".
Does the distinction matter to you?
For day-to-day life, usually less than the name suggests. Symptoms, the value of exercise and the role of tracking are the same across the spectrum. The distinction can matter for how your condition is classified, which treatments guidelines cover at which point, and for research. Some people with nr-axSpA develop X-ray changes over time and their label changes to AS; many do not. The label describes what imaging showed at a point in time, not how severe your symptoms are.
What this means for tracking
Nothing changes. The BASDAI is used across the spectrum; NASS notes that its measurement properties have been shown to hold in non-radiographic axSpA as well (NASS, The Bath Indices). HAVYT’s AS Mode is built around the symptoms — stiffness, pain, fatigue, flares — and is as relevant to someone with nr-axSpA as to someone with AS.