What Is Ankylosing Spondylitis, and Why Does Diagnosis Take So Long?
Ankylosing spondylitis (AS) is a type of inflammatory arthritis that mainly affects the spine and sacroiliac joints. It causes persistent back pain and stiffness, usually starting in early adulthood. Diagnosis often takes years because early symptoms overlap with common mechanical back pain, and standard tests may not show changes until the condition has progressed.
Key takeaways
- AS is a long-term inflammatory condition, not a simple muscle or disc problem.
- It typically begins between the ages of 20 and 40, and is often mistaken for ordinary back pain.
- Average diagnostic delay in the UK is several years, sometimes over a decade.
- Standing whole-body imaging can reveal posture and alignment changes that lying-down scans may miss.
- Diagnosis is a rheumatology decision. Imaging supports that process but does not replace it.
What are the symptoms of ankylosing spondylitis?
The hallmark symptom is inflammatory back pain. Unlike mechanical back pain from a strain or disc issue, AS pain tends to start gradually, often in the lower back and buttocks. It is worse after rest, especially first thing in the morning, and it eases with movement and exercise rather than with sitting still.
Some people also experience pain or swelling in other joints, such as the hips, knees, or ankles. Eye inflammation (uveitis) is another associated condition that can cause redness, pain, and sensitivity to light. If you develop sudden eye symptoms, see a doctor urgently.
Why does ankylosing spondylitis diagnosis take so long?
On average, people with AS wait years from their first symptoms to a confirmed diagnosis. Several factors combine to create this delay.
First, early AS looks a lot like ordinary back pain. Most back pain in young adults is put down to muscle strain or poor posture, especially if there is no obvious injury. GPs see back pain constantly, and the inflammatory pattern can be easy to miss in a short appointment.
Second, standard X-rays of the sacroiliac joints may appear normal in early disease. Visible changes to bone, such as erosion or fusion, can take years to develop. By the time they show clearly on a plain X-ray, the condition may have been present for a long time.
Third, there is no single blood test that confirms AS. The HLA-B27 gene marker is found in many people with the condition, but it is also present in a significant portion of the general population who never develop AS. Inflammatory markers like CRP or ESR may be raised, but they are not specific.
The broader medical term, axial spondyloarthritis, now covers the full spectrum. This includes people who have inflammation visible on MRI but not yet on X-ray (sometimes called non-radiographic axial spondyloarthritis) and those with clear X-ray changes (the classic AS picture). This updated terminology helps catch the condition earlier, but many people still slip through the gaps.
What causes ankylosing spondylitis?
AS is an autoimmune condition. The immune system mistakenly attacks healthy tissue in the joints and ligaments of the spine, causing inflammation. Over time, new bone can form in these inflamed areas, gradually fusing sections of the spine together.
The exact cause is still not fully understood. What is clear is that AS is not caused by poor posture, heavy lifting, or anything you have done wrong. It is a medical condition, not a lifestyle problem.
How does ankylosing spondylitis change your posture over time?
Over years, AS can gradually alter the natural curves of your spine. Inflammation at the edges of the vertebrae triggers new bone growth. This new bone can bridge the gaps between vertebrae, slowly fusing them together. In advanced cases, this is sometimes called a "bamboo spine" because of how it looks on X-ray.
As sections of the spine fuse, normal flexibility is lost. The thoracic spine (upper back) may develop an increased forward curve, pulling your head and shoulders forward. Your lower back may lose its natural inward curve, a change related to flatback syndrome. These shifts affect your overall sagittal balance, which is the way your body lines up from head to feet when seen from the side.
Your body is a connected chain. When one section of the spine stiffens or changes shape, other areas have to compensate. Your hips, knees, and ankles may adjust their position to keep you balanced. This is why people with AS sometimes develop pain in joints well away from the spine itself.
Understanding these postural changes is important for planning any future treatment. A full spine x-ray taken while you are standing shows these alignment shifts as your body actually experiences them, under gravity and load.
How does standing imaging help with ankylosing spondylitis?
Standing whole-body imaging captures your skeleton from head to feet in a single, weight-bearing exposure. This matters for AS because the postural changes the condition causes, the forward lean, the compensatory hip and knee flexion, the loss of natural spinal curves, only show their true extent when you are upright.
When you lie down for a conventional scan, gravity is removed. Your muscles relax. The spine may flatten or straighten in ways that mask how far your alignment has shifted. A standing image shows your body as it actually works throughout the day.
ScanAlign standing EOS imaging uses about 90% less radiation than a standard X-ray, around ten times less. This is particularly relevant if you need repeated imaging over time to monitor changes. The full-length standing view gives your rheumatologist or surgeon a clear picture of overall alignment, not just one region in isolation.
Wondering whether a standing alignment scan could help your consultant understand your AS better? We offer a free video consultation to talk it through.
Book a free video consultationIt is worth being clear: imaging alone does not diagnose AS. Diagnosis is a clinical decision made by a rheumatologist, based on your symptoms, blood tests, examination, and imaging together. What standing imaging adds is a detailed, measurable view of how your posture and alignment have been affected, helping guide the next steps in your care. You can read more on our back pain clinic page.
When is MRI the better choice?
EOS shows bones, joints, and alignment clearly. For detecting early sacroiliac inflammation, disc problems, nerve compression, or soft-tissue changes, MRI is usually the better tool. In suspected early AS, MRI of the sacroiliac joints is often the most sensitive way to spot inflammation before bone changes appear on X-ray. Your rheumatologist will guide which imaging you need.
When should you seek urgent medical attention?
If you experience sudden numbness or weakness in your legs, loss of bladder or bowel control, or severe worsening of symptoms, do not wait for an imaging appointment. Contact your GP, call 111, or go to A&E. These symptoms need urgent assessment.
Frequently asked questions about ankylosing spondylitis
Ankylosing spondylitis is a type of arthritis that causes inflammation in the spine and sacroiliac joints. Over time, it can lead to stiffness and, in some cases, sections of the spine fusing together. It is a long-term condition, not a short-term injury.
Inflammatory back pain typically starts gradually before age 40, improves with exercise but not rest, causes significant morning stiffness lasting 30 minutes or more, and may wake you during the second half of the night. If this pattern sounds familiar, it is worth raising with your GP.
Axial spondyloarthritis is the umbrella term. It covers both AS (where changes are visible on X-ray) and non-radiographic axial spondyloarthritis (where inflammation is present but X-ray changes have not yet developed). Both are the same underlying disease process.
HLA-B27 is a gene marker found in many people with AS. Testing positive means you carry the gene, but it does not mean you have or will develop AS. Many HLA-B27 positive people never get the condition. It is one piece of the diagnostic puzzle, not the whole answer.
No. Diagnosis is a clinical decision made by a rheumatologist. An EOS scan can show the structural and alignment changes that AS causes, such as spinal fusion and posture shifts, which helps inform treatment planning. But it does not replace the blood tests, clinical examination, and specialist assessment needed for diagnosis.
When you lie down, gravity is removed and your muscles relax. This can hide how far your posture has shifted. A standing scan captures your skeleton under load, the way you actually stand and move, so alignment changes are seen as they truly are.
EOS uses about 90% less radiation than a standard X-ray, around ten times less. This lower dose is especially relevant for conditions like AS where imaging may be repeated over time to monitor changes.
No. You can self-refer. We offer a free video consultation first to make sure a standing alignment scan is appropriate for your situation. If a different type of imaging would be more useful, we will tell you.
We are a private, self-pay clinic. You can find current pricing information on our FAQs page or discuss costs during your free video consultation.
Start with your GP. Describe the pattern of your pain clearly: when it is worst, what helps, how long it has lasted. Ask about inflammatory markers and an HLA-B27 test. If your GP suspects AS, they should refer you to a rheumatologist. A standing alignment scan can be useful alongside that process, but it does not replace a rheumatology assessment.
See how your spine is really aligned
A standing whole-body scan shows posture and alignment changes that lying-down imaging can miss. Start with a free video consultation to find out if it is right for you.
Book a free video consultationSources
- National Axial Spondyloarthritis Society (NASS). "About Axial SpA (AS)." nass.co.uk
- Sieper J, Poddubnyy D. "Axial spondyloarthritis." The Lancet. 2017;390(10089):73-84.
- National Institute for Health and Care Excellence (NICE). "Spondyloarthritis in over 16s: diagnosis and management." NICE guideline NG65, 2017.
Written by Abbas Dhami (Specialist Diagnostic Radiographer)
This page is general information and not a diagnosis.
ScanAlign is the trading name of CoreMed Solutions Ltd and operates under The Harley Street Hospital's CQC licence.