Why Ankylosing Spondylitis Is Often Misdiagnosed

Ankylosing spondylitis (AS) has traditionally been thought to primarily affect males, although newer studies suggest otherwise. AS also affects females differently, which leads to misdiagnosis or delayed diagnosis. Although not as frequent, it can also be misdiagnosed in males.

This article covers how AS is diagnosed, why misdiagnosis occurs, and why women are more likely to be misdiagnosed. It also covers how to best advocate for your health care to avoid a delayed AS diagnosis.

How Ankylosing Spondylitis Is Diagnosed

Ankylosing spondylitis can be difficult to diagnose because the condition develops gradually and there is no definitive testing method. If you experience AS symptoms, you should first reach out to a healthcare provider.

Symptoms and Medical History 

In performing a diagnosis, a healthcare provider will first want to know what symptoms you are experiencing. 

Common symptoms of AS include:

• Back pain and stiffness: Back pain and stiffness are primary symptoms that improve with exercise and are worse in the morning and after periods of inactivity. People who experience AS back pain might also experience hip and buttock pain.
  
• Joint pain: AS also causes peripheral arthritis, which is inflammation of the large joints, including the hips and knees. According to the results of a study reported in 2021, the prevalence of peripheral arthritis in AS ranges from 22% to 30%. An affected joint might be painful, tender, swollen, and warm to the touch. 
  
• Enthesitis: AS causes inflammation of the entheses, the site where tendons and ligaments connect to bone. The most common sites for enthesitis are the Achilles tendon (behind the heel), under the heel, and the area where the ribs meet the breastbone.
  
• Fatigue: According to a 2019 report, 50% to 70% of people with AS experience fatigue. AS fatigue isn’t just simply being tired or sleepy. It is debilitating and unrelenting, often affecting your energy levels and motivation. 
  

In addition to your symptoms, your healthcare provider will want to know if other family members have AS or other autoimmune diseases. The HLA-B27 gene, which is strongly linked to AS, is inherited.

One 2014 report finds the heritability of AS to be greater than 95%. Heritability is a measure of how much a trait found in a population is due to genetic variation.

Physical Exam

Your healthcare provider will perform a physical exam to determine what areas of your body are affected by AS. You will be asked to bend your back, neck, and hips in different positions to look for pain and stiffness in these areas.

They will press on some areas of your body to look for tender spots. Your breathing is also checked since breathing troubles are a sign of advanced AS, resulting from lung scarring, chest wall stiffness, and the upper body leaning forward due to spinal changes.

Because AS can lead to neurological symptoms, your healthcare provider will also perform a neurological exam. Neurological symptoms linked to spinal fractures or spinal compression often go unnoticed. Neurological troubles occur in 50% of people with AS who experience spinal fractures, according to a 2015 report.

The neurological exam will assess sensory and motor functions, reflexes, and muscle strength. You should let your healthcare provider know if you experience neurological symptoms like numbness, tingling, muscle weakness, nerve pain, and bowel and bladder dysfunction. 

Additional Tests 

If your healthcare provider suspects AS based on your symptoms and family history, they will request further testing, including blood work, genetic testing, and imaging studies, as follows:

• Blood work: Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) blood tests check levels of inflammation. They generally are elevated for people with AS. Your healthcare provider might also check for rheumatoid factor (RF) to rule out conditions like rheumatoid arthritis (RA).
• Genetic testing: The HLA-B27 gene is common among people with AS, although it can be present in people who do not have AS as well. A positive HLA-B27 blood test is not enough to diagnose AS, but it does prompt your healthcare provider to request further testing, such as imaging studies.
• Imaging studies: X-rays and magnetic resonance imaging (MRI) are the most commonly used imaging tools to diagnose AS. An X-ray allows your healthcare provider to see bones and joints and look for spinal damage and fusing. An MRI can reveal active inflammation and offers a better look at the body’s soft tissues, especially in and around the bones and joints.
  

Why AS Is Difficult to Diagnose

According to a 2012 study, the average AS diagnostic delay was around eight years. That study also found the shortest diagnostic delay was between 2.9 and 5.3 years. Diagnostic delays might be even longer for those previously misdiagnosed with another condition that causes similar symptoms.

AS is a type of autoimmune arthritis that occurs when the immune system malfunctions and attacks healthy tissues—mainly the vertebrae (the small interlocking bones of the spine).

It can be challenging to diagnose because it develops slowly, and symptoms are similar to those of other types of autoimmune arthritis, like psoriatic arthritis and RA. Further, no single test can confirm a diagnosis of AS.

Lag Between First Symptoms and Diagnosis

Back pain is the most common AS symptom. Diagnosis is difficult partly because back pain is a common symptom affecting around 39% of U.S. adults.

AS symptoms typically start in late adolescence and early adulthood, with an incidence rate higher for males. Even so, some healthcare providers do not suspect AS when young people present with back or joint pain.

Research shows severe spinal curvature and fusing can occur without early intervention. Early diagnosis and treatment allow young people to continue being active and productive and prevent problems threatening mobility and independence. 

But the early symptoms of AS—back and joint pain—cannot easily be confirmed as AS. In addition, most people reach out to their primary care providers when they first notice symptoms, and those providers may not recognize the early symptoms of AS or suspect that back pain might be AS.

Other Conditions Can Mimic Symptoms

In its early stages, AS can cause similar symptoms to other types of spondyloarthritis, including psoriatic arthritis and reactive arthritis. But it is distinguishable by the severity of radiological changes it causes in the spine and sacroiliac (SI) joints. The SI joints connect the lower spine and pelvis.

In early AS, radiological evidence cannot be seen clearly on conventional X-rays. And healthcare providers do not typically request MRI scans for low back pain without suspecting a progressive condition like AS. As a result, AS might be misdiagnosed as mechanical back pain. 

While mechanical back pain and AS back pain might seem similar, they are very different. According to the Spondylitis Association of America, mechanical back results from changes in the back due to disruption, such as lifting something heavy or sleeping on an uncomfortable mattress.

On the other hand, inflammatory back pain from AS is persistent, lasts more than three months, and worsens with inactivity. It improves with nonsteroidal anti-inflammatory drugs (NSAIDs) and movement.

No Definitive Test

A diagnosis of AS might be confirmed after a physical exam to confirm inflammatory back pain, enthesitis, and arthritis, X-rays and other imaging, and blood work to check for inflammation and HLA-B27 positivity. 

According to a 2020 Rheumatology report, a healthcare provider can make a diagnosis of AS on specific findings, which include:

• Back symptoms that have lasted three or more months and started before age 40
• Back pain that resolves with exercise and is worse in the morning and after periods of inactivity 
• Limited movement of the low back
• A positive response to NSAIDs 
• Arthritis in the large joints
• Enthesitis 
• Dactylitis (swelling of the fingers or toes)
• Sacroiliitis (inflammation of one or both sacroiliac joints), which can present as buttock and hip pain 
• Additional conditions like uveitis (eye inflammation), psoriasis (an inflammatory skin disease), and inflammatory bowel disease (diseases causing chronic inflammation of the digestive tract)
• Positive family history of AS 
• HLA-B27 positivity 
• High CRP and ESR levels
• Bone inflammation 
• Bone marrow edema

A diagnosis of AS can be made if someone experiences back pain for three or more months and meets other diagnostic criteria.

However, if a healthcare provider does not suspect AS based on factors like age, sex, or nonspecific symptoms (those that can mimic many other diseases), testing to get an AS diagnosis will not be done. A referral to a rheumatologist (a specialist in arthritis conditions like AS) might not be given.

Why Are Women More Frequently Misdiagnosed?

A common misconception about AS is that it rarely occurs in people assigned female at birth, but this isn’t true. According to a 2018 Current Rheumatology Reports article, male-to-female prevalence is around 1.03-to-1. This report also reveals that the disease burden is often higher in females with AS.

A study reported in 2017 in The Journal of Rheumatology found the average delay in diagnosis for females was more than it was for males—8.8 years for females and 6.5 years for males. Besides bias, other factors contributing to delayed diagnosis and misdiagnosis are symptom presentation, disease progression, and radiographic changes.

Symptoms Can Present Differently 

Ankylosing spondylitis symptom presentation is different for people assigned female at birth compared to people assigned male at birth. For example, females with AS report back pain less frequently. But they will report upper back, neck, or widespread pain instead, especially early on, and men report these symptoms less often.

Females with AS will also present with higher disease activity (more symptoms), higher fatigue levels, and more frequent peripheral involvement. They are more likely to experience conditions that go hand-in-hand with AS, including fibromyalgia, inflammatory bowel disease, and psoriasis.

According to the 2018 Current Rheumatology Reports article, females who report widespread pain are twice as likely to receive a misdiagnosis of fibromyalgia. This chronic pain condition causes widespread musculoskeletal pain throughout the body and has some overlapping features with AS.

AS Progresses More Slowly

Radiographic changes due to inflammation can determine disease progression in AS. Progression is also measured based on symptom severity and disease complications.

Studies on AS show radiographic changes are more likely to occur in men. In diagnosing AS, healthcare providers will consider symptoms, patient medical history, blood work, and the physical exam, but X-rays are the most helpful to an AS diagnosis. 

If someone has symptoms of AS but no radiographic evidence, they are less likely to be diagnosed with AS. In some cases, a non-radiographic axial spondyloarthritis (nr-AxSpA) diagnosis is made. But at other times, females presenting with joint symptoms and back pain are diagnosed with other rheumatic conditions more common in females, like RA.

Even with slower radiological progression, people assigned female at birth will have worse outcomes due to delays in diagnosis and other factors, such as sex hormones and treatment response. This is best demonstrated in quality-of-life studies.

The research on quality of life with AS shows females will have a lower quality of life, and such results are consistent with other autoimmune arthritis conditions, including RA.

Radiographic Damage Is Often Subtler

Most studies have shown men with AS have worse radiological progression than women, but this doesn’t mean women do not experience joint damage from AS. Rather, women with ankylosing spondylitis experience less subtle or much different radiographic damage.

For example, hip damage is far worse in males, but females do experience joint damage in the hip and sacroiliac joints.

In addition, males have higher radiographic progression in the lumbar spine (low back), while females tend to experience radiographic progression in the cervical spine (neck). Females might also experience more peripheral arthritis symptoms and damage,

How to Advocate for Your Health Care

A crucial part of getting an accurate diagnosis for AS starts with taking an active role in your health care. You want a healthcare provider to diagnose you properly, and you are an essential part of getting there.

You should reach out to a healthcare provider if you have experienced back pain lasting more than three months. Before your appointment, write down all the symptoms you have experienced and what causes them and improves them. 

Jot down questions you want to ask as you think of them. Being prepared allows you to make the most of your appointment. 

While you want to establish a good relationship with your healthcare provider, it is OK to disagree with them. Rather than becoming defensive or upset, ask questions to help you understand what options make sense.

You might find it hard to speak up when you visit a healthcare provider. But it is vital to get answers to your questions, and they cannot provide answers without your input and action.

If there comes a time when you and your healthcare provider frequently disagree, you often feel rushed, or you cannot get answers to your questions, consider finding a new provider. Not every patient and healthcare provider work well together, which is OK. Making the change means doing what is best for your unique health situation. 

Summary  

Ankylosing spondylitis is a type of spondyloarthritis that affects the small interlocking bones of the spine. It was previously thought to affect males primarily, but the prevalence numbers for males vs. females are almost equal. However, because of such misconceptions, females are frequently misdiagnosed. 

There are additional reasons why misdiagnosis occurs in women, including disease presentation, slower disease progression, and differences in radiographic changes. Although not as frequent, AS can also be misdiagnosed in males.

To ensure you get a timely and accurate diagnosis of AS, you must advocate for yourself. You can do this by preparing for medical appointments, asking questions, and speaking up if you disagree with your medical provider.

A Word From Verywell 

Receiving a diagnosis of ankylosing spondylitis can be scary. But AS is treatable, and medications can prevent long-term disease complications, ease pain, and reduce joint and spine damage. To ensure the best health outcomes, check in with your healthcare provider regularly and take all medications exactly as prescribed.

To ease fears, choose to educate yourself about the condition. You will want to know the symptoms of AS, signs of disease progression, treatment options, lifestyle changes that can help manage symptoms, and when to reach out to your healthcare provider. Being knowledgeable about AS can also help improve your outlook and allow you to cope better with challenges.