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 the condition. 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 why the condition may be more likely to be underdiagnosed among women and members of some minority groups.

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 your sacroiliac joints that 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 (AS) 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. 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 — though health experts estimate axSpA affects about 1 percent of the population, with many of these 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 to other types of spondyloarthritis (SpA). For example, one study searched over 2,000 articles for data on people living with different types of SpA. The researchers found that no studies mentioned how many people were living with nr-axSpA.

Why Is nr-axSpA Underdiagnosed?

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

This means that many people are likely living with this disease who haven’t officially been diagnosed. As a result, the number of cases reported may be much lower than it actually is.

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 criteria that uses 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 to diagnose it. Many people with nr-axSpA also have inflammatory bowel disease (IBD) or uveitis (eye inflammation) that could help point to a diagnosis more quickly. 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 of them also had to see 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 think a person’s inflammatory back pain is caused by stress or an injury rather than a type of arthritis.

Therefore, your rheumatologist will likely have to use magnetic resonance imaging (MRI) scans to take more detailed pictures of the joints in your lower back. They may also run some 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 Struggle To Receive a Diagnosis

Axial spondyloarthritis has historically been thought of as a male disease — but in recent decades, scientists have found that it can affect females as well. 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 still think it’s uncommon in women, which may make it harder for them 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 to males. The female study subjects also had to visit more health care providers and specialists before getting their diagnosis.

Additionally, members of some racial/ethnic minority groups may also 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 it has to do with genetic differences. According to a 2021 research review in Current Opinions on Rheumatology, Black and Hispanic Americans with axSpA are less likely to be HLA-B27 positive. Without this test, doctors and rheumatologists may have a harder time making an accurate diagnosis.

Talk to Your Doctor About Your Symptoms

If you’re experiencing any symptoms of nr-axSpA, talk to your doctor or rheumatologist about getting tested for spondyloarthritis. With so few people living with this disease, it’s important to advocate for yourself and your health. 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 92,000 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 others on MySpondylitisTeam? Share your experience in the comments below, or start a conversation with others on your Activities page.