Prevalence of Nonradiographic Axial Spondyloarthritis (nr-axSpA): Is It Common? | MySpondylitisTeam

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Prevalence of Nonradiographic Axial Spondyloarthritis (nr-axSpA): Is It Common?

Medically reviewed by Neil J. Gonter, M.D.
Written by Emily Wagner, M.S.
Updated on January 2, 2024
Part of the nr-axSpA Doctor Visit Checklist series

Does it ever seem like you’re the only person living with nonradiographic axial spondyloarthritis (nr-axSpA)? It’s easy to think this, especially since researchers and scientists aren’t quite sure how many people in the United States are affected by this form of chronic back pain. Many factors play a role in why there isn’t an accurate count, including recent changes in how nr-axSpA is diagnosed and the fact that the condition is frequently misdiagnosed.

In this article, we’ll discuss how common doctors and researchers believe nr-axSpA is and why it’s been hard to diagnose. We’ll also look at reasons the condition may be more likely to be underdiagnosed among women and members of some minority groups and why talking to your doctor about nr-axSpA is so important.

What Is nr-axSpA?

Nonradiographic axial spondyloarthritis is a type of arthritis (or inflammation) of the joints found in the lower back. Mainly, it affects the sacroiliac joints, which connect the bottom of your spine to your pelvis. The most common symptom of nr-axSpA is lower back pain.

Although the pain from nr-axSpA is very real, diagnosing the disease can be difficult. In other types of inflammatory arthritis — like ankylosing spondylitis and psoriatic arthritis — joint damage can be seen on imaging tests like X-rays. However, signs of joint damage from nr-axSpA don’t show up on X-rays, which is why “nonradiographic” is part of the condition’s name. Symptoms can also be similar to some of those seen in other rheumatic diseases, such as rheumatoid arthritis. This can make getting an accurate diagnosis difficult, leading to many doctors’ visits and repeated testing.

How Many People in the U.S. Are Living With nr-axSpA?

Studies have noted that the exact prevalence of nr-axSpA is unknown, but health experts estimate that axSpA affects about 1 percent of the U.S. population, with many of these people still undiagnosed. According to the Spondylitis Association of America, about 1.6 million Americans are living with nr-axSpA.

However, many studies don’t report how many people in the general population have nr-axSpA compared with other types of spondyloarthritis. In one study, researchers looked at over 2,000 articles for data on people who had different types and found that none mentioned how many were living with nr-axSpA. This is partly to do with newer classification criteria for different types of spondyloarthritis.

Why Is nr-axSpA Underdiagnosed?

Without accurate data from many studies, doctors and researchers can’t be exactly sure how prevalent nr-axSpA is. Many believe that more people have nr-axSpA than research shows. However, the condition itself can be hard to diagnose.

This means it’s likely that many people living with this inflammatory disease haven’t officially received a diagnosis of nr-axSpA. As a result, the number of reported cases may be much lower than actual cases.

Following are some reasons getting an nr-axSpA diagnosis can be so difficult.

It’s a Newly Recognized Disease

Although nr-axSpA has long existed, doctors and researchers didn’t have a good way to diagnose it until 2009. The Assessment of SpondyloArthritis International Society created a set of diagnostic criteria that use a person’s symptoms and imaging test results to confirm an nr-axSpA diagnosis.

These criteria have been around for only about 14 years, and primary care physicians and rheumatologists are still learning about the symptoms of nr-axSpA. Many people with nr-axSpA also have inflammatory bowel disease (IBD) or uveitis (eye inflammation) that could help point to a diagnosis more quickly. Some people with axSpA also report experiencing jaw pain and changes to their skin and nails, such as those seen in psoriasis. Your doctor or rheumatologist might not know that your other symptoms could be connected.

It’s also common for people to wait several years and meet with many health care providers before they finally get an accurate diagnosis. A 2020 study of 125 people with nr-axSpA found that 50 percent of participants had seen at least four health care providers before being referred to a rheumatologist. Around half also saw at least two rheumatologists before getting answers.

Joint Damage From nr-axSpA Can’t Be Seen With X-Rays

Since signs of nr-axSpA can’t be seen with X-rays, many doctors and rheumatologists have a hard time diagnosing the condition. They might attribute a person’s inflammatory back pain to stress or an injury rather than a type of arthritis.

Your rheumatologist will likely use magnetic resonance imaging (MRI) scans to take more detailed pictures of the joints in your lower back. They may also run blood tests to look for a genetic marker for autoimmune diseases known as HLA-B27. People with axSpA tend to be positive for HLA-B27.

Women and People of Color May Have Trouble Getting a Diagnosis

Axial spondyloarthritis has historically been thought of as a male disease, but in recent decades, scientists found that it can affect females too. In fact, men and women have an equal risk of developing nr-axSpA, according to a 2020 study in Seminars in Arthritis and Rheumatism. Still, some rheumatologists think it’s uncommon in women, who may find it harder to receive an nr-axSpA diagnosis.

Women also may be underdiagnosed because, according to the 2020 study, they tend to experience back pain less often than men — instead, they’re more likely to report joint pain and morning stiffness, pelvic or heel pain, IBD, and psoriasis (an inflammatory skin condition).

Potential gender bias and a lack of understanding of how ax-SpA affects females may contribute to underdiagnosis or misdiagnosis. A 2021 study in Clinical Rheumatology found that, on average, it took females one to two years longer to receive an axSpA diagnosis compared with males. The female participants also had to visit more health care providers and specialists before getting their diagnosis.

Additionally, members of some racial/ethnic minority groups may be underdiagnosed — though researchers aren’t sure how much of that has to do with factors such as racial bias and health care inequity and how much is related to genetic differences. According to a 2021 research review in Current Opinion in Rheumatology, Black and Hispanic Americans with axSpA are less likely to be positive for HLA-B27. Without this test, doctors and rheumatologists may have a harder time making an accurate diagnosis.

Active or Stable?

Active disease occurs when nr-axSpA causes inflammation, prompting you to feel symptoms such as low back pain, stiffness, and fatigue. Stable disease means that for the past six months, either you’ve had no symptoms or your symptoms were managed well with your current treatment. Your doctor will evaluate whether your inflammatory arthritis is active or stable, which will influence the treatment options that your doctor may recommend.

Read more about active and stable nr-axSpA.

Talk to Your Doctor About Your Symptoms

Talk to your doctor or rheumatologist about getting tested for spondyloarthritis if you think you have symptoms of inflammatory back pain. It’s important to advocate for yourself and your health, even if it means you need to see multiple doctors. Bringing up your concerns can help you get a diagnosis and start proper treatment sooner to improve your symptoms and overall quality of life.

Talk With Others Who Understand

On MySpondylitisTeam, the social network for people with spondylitis and their loved ones, more than 95,000 members come together to ask questions, give advice, and share their stories with those who understand life with spondylitis.

Have you met any other people with nonradiographic axial spondyloarthritis? Does it help to connect with others on MySpondylitisTeam? Share your experience in the comments below, or start a conversation with others on your Activities page.

  1. Nonradiographic Axial Spondyloarthritis: Clinical and Therapeutic Relevance — Arthritis Research & Therapy
  2. How Non-Radiographic Axial Spondyloarthritis Is Diagnosed: What To Expect at the Doctor — CreakyJoints
  3. Ankylosing Spondyloarthritis — Mayo Clinic
  4. Prevalence of Axial Spondyloarthritis in United States Rheumatology Practices: Assessment of SpondyloArthritis International Society Criteria Versus Rheumatology Expert Clinical Diagnosis — Arthritis Care & Research
  5. Incidence and Prevalence of Axial Spondyloarthritis: Methodologic Challenges and Gaps in the Literature — Clinical and Experimental Rheumatology
  6. The Diagnostic Prevalence of AS and axSpA Are Rising in the U.S. What Does It Mean? — Spondylitis Association of America
  7. Overview of Non-Radiographic Axial Spondyloarthritis (nr-axSpA) — Spondylitis Association of America
  8. Nonradiographic Axial Spondyloarthritis: Expanding the Spectrum of an Old Disease — Medicine
  9. Rheum to Diagnosis’: Uncovering Impediments to Accurate Diagnosis of Non-Radiographic Axial Spondyloarthritis (nr-axSpA) — American College of Rheumatology Meeting Abstracts
  10. Non-Radiographic Axial Spondyloarthritis (nr-axSpA): Advances in Classification, Imaging and Therapy — Rheumatology and Therapy
  11. HLA-B27 Antigen — University of Rochester Medical Center
  12. Understanding Differences Between Men and Women With Axial Spondyloarthritis — Seminars in Arthritis and Rheumatism
  13. Gender Differences in Patient Journey to Diagnosis and Disease Outcomes: Results From the European Map of Axial Spondyloarthritis (EMAS) — Clinical Rheumatology
  14. Racial Differences in Clinical Features and Comorbidities in Ankylosing Spondylitis in the United States — The Journal of Rheumatology
  15. Educational Needs and Challenges in Axial Spondyloarthritis — Current Opinion in Rheumatology
  16. 2019 Update of the American College of Rheumatology/Spondylitis Association of America/Spondyloarthritis Research and Treatment Network Recommendations for the Treatment of Ankylosing Spondylitis and Non-Radiographic Axial Spondyloarthritis — Arthritis Care & Research

Updated on January 2, 2024
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Neil J. Gonter, M.D. is an assistant professor of medicine at Columbia University. Learn more about him here.
Emily Wagner, M.S. holds a Master of Science in biomedical sciences with a focus in pharmacology. She is passionate about immunology, cancer biology, and molecular biology. Learn more about her here.

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