History of Axial Spondyloarthritis Classifications

Reviewed by: HU Medical Review Board | Last reviewed: October 2022

The condition that doctors now call axial spondyloarthritis (axSpA) was first mentioned in about 1500 BC. Ancient Egyptian pharaohs may have had a form of the disease. But it was not until recent decades that major advances in how doctors understand axSpA were made.1

This is especially true for ankylosing spondylitis (AS), also known as radiographic axSpA (r-axSpA). With the widespread use of X-rays, spinal fusion became the hallmark of diagnosing AS. Spinal fusion is when 2 or more bones in the spine join (fuse) together.1

Early classification

Doctors thought AS was progressive rheumatoid arthritis (RA) until 1893. That year, a neurologist named Vladimir Bekhterev claimed AS was a separate disease. This is why AS was once known as Bekhterev’s disease.1

Changes to early classification

In the 1970s, doctors began to recognize that several types of arthritis were highly related. They placed them in a general category that would later be called spondyloarthritis. From the 1970s to the early 2000s, doctors divided spondyloarthritis into these groups:2

  • Ankylosing spondylitis (AS)
  • Psoriatic arthritis (PsA)
  • Reactive arthritis
  • Arthritis linked to inflammatory bowel disease (IBD)
  • Undifferentiated spondyloarthritis, which does not match any of the other subtypes

In 1984, doctors updated a standard set of rules for diagnosing AS. These rules were called the New York criteria. They required severe inflammation and damage to the sacroiliac joints (sacroiliitis) to be visible on an X-ray.1,2

But then magnetic resonance imaging (MRI) came into greater use. Doctors realized that people could have back pain and other symptoms long before joint damage appeared on X-rays.1,2

Spondyloarthritis today

Today, the Spondylitis Association of America defines spondyloarthritis as a “family of closely related diseases.” These conditions share several features. Inflammatory back pain is the most common.3

Under today's guidelines, there are 2 main types of spondyloarthritis:3

Axial spondyloarthritis

AxSpA mainly affects the spine, but it can also affect other joints in the body. AxSpA is further broken down into 2 types:3

  • Radiographic axSpA (r-axSpA or AS), where inflammation shows on X-rays
  • Non-radiographic axSpA (nr-axSpA), where changes do not appear on X-rays

Peripheral spondyloarthritis

People whose symptoms are mostly outside the spine are diagnosed with pSpA. Several conditions are now considered to fall under the pSpA umbrella. These include:3,4

  • Psoriatic arthritis (PsA)
  • Reactive arthritis
  • Arthritis with IBD
  • Undifferentiated spondyloarthritis

These condition definitions are more specific than they were in the past. That means doctors can diagnose patients earlier and more accurately.1

Classifying versus diagnosing

It is important to know that classifying axSpA is different from diagnosing it. Your doctor will diagnose axSpA according to your:5

  • Symptoms
  • Medical history
  • Various lab or X-ray tests

Once your doctor diagnoses axSpA, classifying the type comes next. Having inflammatory back pain alone does not mean you have AS. But this symptom is an important part of an AS diagnosis.5

People with axSpA often report that it takes a long time to be diagnosed. While changes to classification have improved this, there is still more work to be done. Talk to your doctor if you have questions about axSpA.5

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