Axial Spondyloarthritis: Understanding the Challenges Doctors Face in Making the Diagnosis

Table of Contents

• Key Points
• Background: What Is Axial Spondyloarthritis?
• General Principles of Diagnosis: Why It Is So Difficult
• Building Block 1: Age When Back Pain Starts
• Building Block 2: Patient History and Physical Examination
• Building Block 3: Laboratory Testing (CRP and HLA-B27)
• Building Block 4: Imaging Studies (X-Rays and MRI)
• Differential Diagnosis: Other Conditions That Mimic axSpA
• The Usual Approach to Diagnosing axSpA and How Doctors Build Their Skills
• Pitfall 1: Using Classification Criteria as Diagnostic Criteria
• Pitfall 2: Diagnosing by Simply Counting SpA Features
• Pitfall 3: Over-Reliance on Imaging Findings
• Final Thoughts and What To Do if the Diagnosis Is Unclear
• Practice Points for Doctors (and What Patients Should Know)
• Frequently Asked Questions
• Source Information

Key Points

• No single test, symptom, or imaging finding can confirm or rule out axial spondyloarthritis by itself.
• In a worldwide study of 2,579 patients, 92% developed axial symptoms before age 45.
• Using research classification criteria as diagnostic tests is a common pitfall and misclassifies many patients.
• Counting SpA features is insufficient; even with four or more features, about 15% of patients did not have axial spondyloarthritis.
• MRI bone marrow edema also occurs in healthy people, runners, and postpartum women, so imaging must be interpreted with clinical context.

Background: What Is Axial Spondyloarthritis?

Axial spondyloarthritis (axSpA) is a chronic inflammatory rheumatic disease (a type of autoimmune-related condition that causes joint inflammation). It mainly affects the spine and the sacroiliac (SI) joints — the joints connecting the lower spine to the pelvis. Inflammation in these areas causes back pain and stiffness.

Beyond the spine, other symptoms are common. Peripheral manifestations affect the limbs and include arthritis (joint inflammation in the arms or legs), enthesitis (inflammation where tendons or ligaments attach to bone), and dactylitis (whole-finger or whole-toe swelling, sometimes called "sausage digit"). Extra-musculoskeletal manifestations (EMMs) affect other body systems and include inflammatory bowel disease (IBD, chronic inflammation of the digestive tract), psoriasis (PSO, a skin condition with scaly patches), and anterior uveitis (AU, inflammation inside the eye). Together, these features contribute to the overall burden of axSpA.

AxSpA is divided into two subtypes:

• Non-radiographic axSpA (nr-axSpA): Patients have symptoms but no definite signs of sacroiliitis (SI joint inflammation) visible on conventional X-rays.
• Radiographic axSpA (r-axSpA): Previously called ankylosing spondylitis (AS). These patients do have definite sacroiliitis visible on conventional X-rays.

For the most part, the clinical presentation and management of the two forms are very similar. One exception matters: some r-axSpA patients have extensive spinal damage. For them, preventing progressive spinal damage — and occasionally surgically correcting spinal deformity — becomes an important part of care.

The nr-axSpA versus r-axSpA distinction is still clinically important for two reasons. First, regulatory agencies like the US Food and Drug Administration (FDA) and the European Medicines Agency (EMA) require clinical trials to be performed in both disease forms before approving new pharmaceutical treatments. Second, the rate of spinal damage progression differs: damage mainly develops in patients with r-axSpA, not nr-axSpA.

General Principles of Diagnosis: Why It Is So Difficult

axSpA has a highly varied (heterogeneous) presentation. No single feature from a patient's history, physical examination, laboratory testing, or imaging studies has enough sensitivity and specificity to diagnose — or exclude — axSpA on its own.

Sensitivity means how well a test catches people who truly have the disease. Specificity means how well it rules out people who do not. For axSpA, every feature falls short on at least one of these measures when used alone.

Because back pain is usually the main complaint that triggers a diagnostic workup, diagnosis involves two mental tasks happening at once. The doctor must recognize a pattern of features that, taken together, provides enough evidence to diagnose the disease. At the same time, the doctor must exclude other potential causes of back pain — called the differential diagnosis.

Building Block 1: Age When Back Pain Starts

axSpA usually begins in the second or third decade of life — meaning the teens, twenties, and thirties. Starting after age 45 is uncommon. That makes the age at onset of the first back pain symptoms a very useful, easy, and accessible piece of information for the first selection of patients with chronic back pain.

Most evidence originally came from European studies. A recent international study confirms the same pattern worldwide. The Assessment of SpondyloArthritis international Society (ASAS)-PerSpA study included 2,579 axSpA patients, and 92% had developed axial symptoms (spine-related symptoms) before age 45.

Strikingly, the results varied little across geographical regions:

• Asia: 574 patients, 94% had symptom onset before age 45
• Europe and North America: 998 patients, 92%
• Latin America: 246 patients, 89%
• Middle East and North Africa: 771 patients, 91%

The study also confirmed earlier findings about who tends to develop symptoms earlier. Age at onset of axial symptoms was consistently lower in HLA-B27-positive patients (people carrying the main genetic risk factor for axSpA) — a median of 25 years (IQR 19–32) versus 31 years (IQR 22–39) in HLA-B27-negative patients. Men also tended to develop symptoms earlier than women: a median of 25 years (IQR 19–33) versus 28 years (IQR 21–37).

However, after statistical adjustment (multivariable models), an independent effect of male gender beyond HLA-B27 was only found in Asian patients. The bottom line for patients: around the world, the vast majority of people with axSpA develop back pain before age 45. Back pain that starts well after 45 is unlikely to be axSpA.

Building Block 2: Patient History and Physical Examination

The medical history of any back pain patient suspected of having axSpA should always cover the duration and characteristics of the pain. In particular, doctors look for features suggesting an inflammatory cause. Inflammatory back pain differs from mechanical back pain: it tends to be worse at rest, improves with exercise, and often wakes people in the second half of the night.

Several sets of questions have been published over time, aiming to identify a history suggestive of inflammatory back pain (IBP). The most recent and widely used are the ASAS expert criteria for IBP. A patient is classified as having IBP if at least 4 out of these 5 features are present:

1. Age at onset under 40 years
2. Insidious (gradual) onset rather than sudden
3. Improvement with exercise
4. No improvement with rest
5. Pain at night (with improvement upon getting up)

In the original publication validating these criteria, the presence of 4 of the 5 features had a sensitivity of 80% and a specificity of 74%, using overall expert judgment on IBP as the gold standard. In plain terms: 80% of people judged by experts to have IBP were correctly identified by the criteria, and 74% of people without IBP were correctly excluded.

Because the questions are easy to apply, IBP is commonly used in referral recommendations directing patients with back pain to rheumatologists. As a result, IBP is very common among the patients who actually arrive in a rheumatologist's office. The downside: several publications have reported a reduced discriminative value of IBP in that setting. In other words, once you are already seeing a rheumatologist because your doctor suspected axSpA, "Do you have inflammatory back pain?" is a less powerful question than it was for selecting patients in the first place.

A thorough history also covers other SpA features. The doctor will ask about:

• Current or past arthritis (joint inflammation), enthesitis, or dactylitis
• Psoriasis, inflammatory bowel disease, and acute anterior uveitis
• Family history of SpA, including uveitis and axSpA in family members

Response to nonsteroidal anti-inflammatory drugs (NSAIDs, such as ibuprofen, naproxen, or diclofenac) is also informative. Although back pain of many causes may improve with NSAIDs, marked improvement in pain within one or two days of starting NSAIDs supports an axSpA diagnosis.

History taking must also pursue the alternative explanations for back pain. Doctors should ask about previous episodes of back pain or injury, back surgery, weight loss and fever, neurological symptoms (like numbness or weakness), and widespread pain.

Physical examination is an important part of the diagnostic workup. It usually includes:

• Examining the joints for arthritis
• Examining the heels for enthesitis of the Achilles tendon
• Checking the hands and feet for dactylitis
• Checking the nails and skin for psoriasis

Signs of active acute uveitis are not commonly detected by rheumatologists in patients with back pain, but when present they greatly increase the likelihood of axSpA.

Doctors can measure spinal mobility restriction in several ways. Commonly used measures include cervical rotation (how far you can turn your head), chest expansion (to measure the range of motion of the costovertebral joints), the Schober test (range of motion of the lower spine in the sagittal plane, i.e., bending forward), and lateral spinal flexion (bending sideways). Age-stratified reference intervals for various spinal mobility measurements in Europeans have been published and are freely available through the ASAS website (https://www.asas-group.org/instruments/mobility-curves/).

Unfortunately, spinal mobility tests have limited diagnostic value. Spinal mobility varies greatly among normal individuals and decreases with advancing age. Also, in a cohort of chronic back pain patients suspected of having early axSpA — the SPACE cohort, discussed further below — impaired spinal mobility occurred just as often in patients with early axSpA as in patients with other forms of chronic back pain.

Building Block 3: Laboratory Testing (CRP and HLA-B27)

C-reactive protein (CRP), a marker of inflammation produced by the liver, should be measured in patients suspected of having axSpA. Elevated CRP levels are seen in only about 25–40% of patients with axSpA. This means the majority of axSpA patients have a normal CRP — so a normal level definitely does not rule out the disease.

CRP levels also serve another function beyond diagnosis. They are part of the ASDAS (Axial Spondyloarthritis Disease Activity Score), a composite measure of disease activity preferred for axSpA. Over time, elevated CRP is associated with spinal radiographic progression — meaning visible damage on X-rays. When CRP testing is unavailable, the erythrocyte sedimentation rate (ESR, another inflammation blood test) is an alternative. An elevated CRP or ESR could also be caused by something entirely unrelated to axSpA.

HLA-B27 (human leukocyte antigen B27) is a genetic marker and by far the most important single genetic risk factor for axSpA. axSpA is a complex polygenic disease, meaning many genes contribute, but HLA-B27 dominates. Worldwide, HLA-B27 prevalence varies enormously between populations: less than 1% in some Sub-Saharan African studies, up to over 30% in Northern Arctic communities such as the Chukchi and Inuit. The prevalence of HLA-B27 in a given population mirrors the prevalence of axSpA there, underscoring its importance in disease development.

The diagnostic value of HLA-B27 testing comes from the fact that HLA-B27 is consistently far more common in axSpA patients than in the general population. In the ASAS-PerSpA study mentioned earlier:

• 89% of axSpA patients from Asia were HLA-B27 positive
• 65% from the Middle East and North Africa
• 81% from Latin America
• 78% from Europe and North America

For reference, only about 6–8% of the general population in Europe and North America carries HLA-B27. So a positive test meaningfully shifts the probability, although it is not a diagnosis by itself — and many HLA-B27-positive people never develop axSpA.

Building Block 4: Imaging Studies (X-Rays and MRI)

Imaging plays an important role in diagnosing axSpA. Inflammation may occur throughout the entire spine, but it is easiest to detect in the sacroiliac (SI) joints — the joints where the spine meets the pelvis. At many centers, a plain radiograph (X-ray) of the pelvis remains the first imaging study, because it can show sacroiliitis and is less expensive and resource-intensive than MRI (magnetic resonance imaging).

On radiographs, the right and left SI joints are graded separately according to how much damage is visible. The grading scale is:

• Grade 0: Normal
• Grade 1: Suspicious changes
• Grade 2: Minimal abnormality — small localized areas with erosions or sclerosis (hardening of bone), without alteration in joint width
• Grade 3: Unequivocal abnormality — moderate or advanced sacroiliitis with one or more of the following: erosions, sclerosis, joint space widening, narrowing, or partial ankylosis (fusion)
• Grade 4: Total ankylosis (complete fusion of the joint)

According to this grading system, a radiograph counts as positive for sacroiliitis if the score is grade 2 or higher on both sides (bilaterally), or grade 3 or higher on one side (unilaterally). Examples of radiographs at different grades are available in the ASAS slide library under "X-ray" (www.asas-group.org/education/asas-slide-library/).

However, X-rays have serious limitations for early disease. Patients may have symptoms from sacroiliitis for several years before any abnormality becomes visible on radiography. Emerging data also suggest that the transition from non-radiographic to radiographic axSpA is a slow process, and many nr-axSpA patients may never develop visible X-ray abnormalities at all. Furthermore, interpreting SI joint X-rays is not always easy: interobserver and intra-observer variation is substantial, meaning sacroiliitis can be missed or wrongly assumed to be present.

In patients who already have obvious sacroiliitis on X-ray, additional imaging such as MRI may not be necessary for diagnosis. But MRI is capable of detecting inflammation in the SI joints before any change appears on X-ray. Unlike plain radiographs, MRI can reveal inflammatory changes (such as bone marrow edema — essentially fluid and inflammation inside the bone), fatty changes, and more subtle structural abnormalities. MRI also shows better interreader reliability than conventional radiography, meaning different doctors reading the same scan are more likely to agree.

For patients whose initial MRI of the SI joints is negative (no sacroiliitis visible), a follow-up MRI can generally be considered when axSpA is still suspected. But the chance that a negative MRI becomes positive at follow-up after 3–12 months is very low — particularly for women (2.8%) and for HLA-B27-negative patients (1.5%). The conversion rate is somewhat higher for men (12%) and for HLA-B27-positive patients (11%).

Routine MRI or radiography of the spine is not standard in the diagnosis of axSpA. However, it can be very useful when a doctor suspects a condition other than SpA, or to actively rule out other causes of back pain.

Differential Diagnosis: Other Conditions That Mimic axSpA

Many conditions that cause chronic spinal and low back pain can look like axSpA. In the Spondyloarthritis Caught Early (SPACE) cohort — a study of chronic back pain patients referred to a rheumatologist, with back pain onset before age 45 and symptom duration under two years — the common diagnoses in patients who did not have axSpA were:

• Non-specific back pain
• Mechanical back pain
• Inflammatory back pain without SpA
• Degenerative disc disease
• (Fibro)myalgia

It is important to remember that those chronic back pain patients were young adults with a mean age under 30 years. In other groups of chronic back pain patients — especially older patients — other causes become more likely. Those include osteoporotic fractures (fractures from weakened bone), osteoarthritis of the spine, malignancy (cancer), and diffuse idiopathic skeletal hyperostosis (DISH, a condition with abnormal bone growth along the spine).

The Usual Approach to Diagnosing axSpA and How Doctors Build Their Skills

Having a mental picture of a typical disease presentation helps with identification and workup. The authors, who practice in Western Europe, describe a typical axSpA patient this way: a young adult with chronic inflammatory back pain (or at least several features associated with IBP) located in the lower back, starting before age 40 to 50, usually HLA-B27 positive, with one or two other SpA features, and clear signs of sacroiliitis on imaging.

But the authors stress that axSpA is heterogeneous — many patients do not follow this typical picture. One rule guides their practice: they are very reluctant to diagnose axSpA if no signs of active inflammation or post-inflammatory structural lesions can be found in the SI joints or the spine.

To build diagnostic skills, the authors strongly recommend training in three areas: assessing clinical signs of SpA, recognizing patterns, and interpreting images. Educational initiatives are underway worldwide. One free resource is the ASAS interactive online case library (www.asas-group.org/education/asas-case-library), which contains over 30 clinical cases spanning the full spectrum of axSpA and the most common differential diagnoses. Each case discusses imaging in the context of clinical findings and laboratory results.

The authors then present the three pitfalls they encounter most commonly in clinical practice.

Pitfall 1: Using Classification Criteria as Diagnostic Criteria

Classification criteria for axSpA exist, but they serve a research purpose, not a patient-care purpose. These criteria are standardized definitions designed to create well-defined, relatively homogeneous groups of patients for clinical and laboratory research. The current version is the 2009 ASAS classification criteria for axSpA.

To be classified as having axSpA for a research study, a patient must fulfill the entry criterion: chronic back pain lasting more than three months, starting before age 45. Then, one of two pathways must be satisfied:

• Imaging pathway: Sacroiliitis on imaging (active inflammation on MRI highly suggestive of SpA, OR definite radiographic sacroiliitis per the modified New York criteria) PLUS at least one other SpA feature.
• HLA-B27 pathway: HLA-B27 positive PLUS at least two other SpA features.

The other SpA features listed in the 2009 ASAS criteria include all the items discussed in this article: inflammatory back pain, arthritis, enthesitis (heel), dactylitis, psoriasis, inflammatory bowel disease, acute anterior uveitis, good response to NSAIDs, and family history of SpA.

At first glance, these criteria look easy to use for diagnosis too. They are not. Using classification criteria as diagnostic criteria creates two problems. First, it ignores the crucial issue of differential diagnosis — a feature list does not consider whether something else better explains the symptoms. Second, it produces an unacceptable number of misdiagnoses in both directions: axSpA patients incorrectly not diagnosed (because the criteria have too low sensitivity for diagnosis), and patients without axSpA incorrectly labeled as having it (because the criteria have too low specificity for diagnosis).

These limitations stem, in part, from the categorical nature of classification criteria — a patient either fulfills them or does not. Real clinical diagnosis, by contrast, allows flexibility and encompasses a broad spectrum of diagnostic confidence.

The numbers confirm the problem. In a meta-analysis of 4,990 patients from seven studies, the sensitivity of the ASAS axSpA classification criteria was 82% (95% confidence interval 77–96%), and the specificity was 87% (95% confidence interval 78–92%). A test that misses roughly 18 out of every 100 true cases, and falsely labels about 13 out of every 100 non-cases, is not an acceptable diagnostic tool on its own.

Pitfall 2: Diagnosing by Simply Counting SpA Features

In a patient with chronic back pain, each additional SpA feature increases the chance that the pain is caused by axSpA. Every feature carries some diagnostic weight, and multiple features make axSpA progressively more likely. To help doctors, a formal diagnostic algorithm exists. The ASAS-modified Berlin algorithm suggests that a patient with chronic back pain who has 4 or more SpA features can be diagnosed with axSpA without further imaging or HLA-B27 testing.

The authors stress that this algorithm is only a decision aid for rheumatologists. It cannot and should not replace a proper differential diagnostic assessment in patients with chronic back pain.

The reason: SpA features are extremely diverse. They range from genetic risk (HLA-B27), to inflammation in the peripheral skeleton (arthritis), to inflammation in the axial skeleton (sacroiliitis on MRI), to inflammation outside the joints (psoriasis). The features must be combined into a meaningful pattern that points toward inflammation in the axial skeleton.

Consider this example from the article: a patient with peripheral spondyloarthritis has psoriasis, arthritis, and dactylitis — already three SpA features. If that patient develops chronic back pain, the pain does not automatically mean axSpA. The three existing features raise suspicion, but the back pain could easily have an entirely different mechanical cause.

The SPACE cohort quantified this issue. In 500 patients suspected of having axSpA, a diagnosis was eventually made in 250 patients (50%). The rate of confirmed axSpA rose steadily with the number of SpA features:

• 1 or fewer SpA features: axSpA in 24% of patients
• 2 SpA features: 43%
• 3 SpA features: 62%
• 4 or more SpA features: 85%

This shows two things. More features indeed make axSpA more likely. But it also shows that even numerous SpA features do not automatically produce an axSpA diagnosis: 15% of patients with four or more features (about 1 in 7) turned out not to have axSpA. Counting alone is therefore insufficient. Clinical reasoning about alternative explanations remains essential.

Pitfall 3: Over-Reliance on Imaging Findings

Imaging — whether X-ray or MRI — detects inflammation or post-inflammatory changes in the spine and SI joints, and it plays a very important role in diagnosing axSpA. Over-reliance on imaging, however, leads to misdiagnosis.

X-rays of the SI joints cannot detect axSpA when structural damage has not yet occurred, and they suffer from substantial intra- and inter-reader variability (the same reader, or different readers, may grade the same image differently). MRI is therefore increasingly used to visualize inflammation in the SI joints. MRI can detect various lesions associated with axSpA, but bone marrow edema (BME) — visible as bright spots indicating active inflammation inside the bone — has been, and still is, considered the most diagnostically useful finding.

The MRI definition of sacroiliitis has evolved. In the first definition in 2009, only BME reflecting active sacroiliitis counted as a relevant lesion. Knowledge of structural lesions on MRI has grown since then. The revised 2016 ASAS definition still centers on detecting BME typical of SpA, but it now acknowledges the additional diagnostic value of concomitant structural lesions — such as erosions (bone surface damage), bony ankylosis (fusion), and fat metaplasia (fatty changes in bone marrow). These structural lesions matter most when BME findings are doubtful; they can increase diagnostic confidence.

The usefulness of MRI is limited by two factors. First, interpreting these images is difficult, especially without special training. Second, MRI must be interpreted in the context of the degree of clinical suspicion — an MRI finding means something different in a patient with high clinical probability than in a patient with low probability.

Other causes of BME in the SI joints, especially mechanical stress, must always be considered. Multiple studies have reported SI joint BME in people without axSpA:

• In 47 Dutch healthy volunteers, 23% had an MRI "positive for sacroiliitis," compared with 92% of 47 axSpA patients and only 6% of 47 patients with chronic back pain.
• 13% of 24 runners had a "positive MRI."
• 57% of 7 women with postpartum (after childbirth) low back pain had a "positive MRI."

None of the BME findings in the people without axSpA included deep lesions (defined as a homogeneous signal extending at least 1 cm from the joint surface). And the more SI joint quadrants or MRI slices showing BME, the higher the likelihood that the lesion was due to axSpA.

A Danish study found that in recreational runners and elite ice-hockey players, 30–41% had BME that fulfilled the ASAS definition, with the posterior lower ilium as the most frequently affected quadrant. Erosions were virtually absent in these healthy athletes.

The takeaway: just like sacroiliitis on X-rays, MRI findings of BME alone are not necessarily diagnostic of axSpA. MRI must always be interpreted in the context of clinical and laboratory findings.

Final Thoughts and What To Do if the Diagnosis Is Unclear

Pharmaceutical treatment options for axSpA are rapidly increasing. Key goals of management are to control symptoms, restore function and quality of life, and slow disease progression. Obviously, appropriate treatment must be preceded by a correct diagnosis — treating the wrong disease helps no one.

The authors acknowledge that diagnosing axSpA remains challenging, even though diagnostic tools — including MRI and more readily available HLA-B27 testing — have clearly improved. The bigger unsolved problem is that many people with suspected axSpA never reach a rheumatologist in the first place; referral pathways remain imperfect.

Even under almost optimal diagnostic circumstances, diagnostic uncertainty remains for a number of patients. This reflects the fundamentally heterogeneous nature of the disease. For patients in whom the diagnosis cannot be made with confidence, the authors advise doctors to:

• Avoid making a definitive conclusion one way or the other
• Regularly discuss cases with fellow rheumatologists and radiologists, especially those with expertise in musculoskeletal radiology

For now, the available data suggest that repeating MRI within one year has a low yield and is generally not diagnostically useful. In other words, a repeat scan after just a few months is unlikely to change the picture — patience and clinical follow-up matter more.

Practice Points for Doctors (and What Patients Should Know)

The article closes with practice points, which patients may find useful for understanding what a good diagnostic process should look like:

• No single pathognomonic feature (a feature that alone proves the disease) exists for axSpA. Diagnosis is a skill that involves recognizing a pattern of features that, taken together, provides sufficient evidence.
• A typical presentation in Western Europe is a young adult with chronic inflammatory back pain beginning before age 40–50, usually HLA-B27 positive, with one or two other SpA features and clear sacroiliitis on imaging.
• Back pain that starts after age 45 is unlikely to be axSpA, where the vast majority (92% worldwide) of patients have symptom onset before 45.
• Classification criteria are for research, not diagnosis; they misclassify too many individuals on both sides.
• Counting SpA features helps but is insufficient — even with 4 or more features, about 15% of patients do not have axSpA, and a patient with peripheral SpA features plus back pain still needs an assessment of whether the back pain is truly axial.
• MRI findings must be weighed against clinical suspicion, because BME appears in healthy people (23% of healthy volunteers in one Dutch study), runners (13–41%), and postpartum women (57% in a small study), often without deep lesions or erosions.

For patients, the most practical message from this paper is simple: a diagnosis of axSpA is a medical judgment that integrates your story, your examination, your blood tests, and your imaging — not any single one of those in isolation. If you are being evaluated for chronic back pain, a thoughtful rheumatologist will consider both what supports axSpA and what else could explain your symptoms. That balanced approach is the standard of care.

Frequently Asked Questions

What is axial spondyloarthritis and how is it different from ankylosing spondylitis?

Axial spondyloarthritis is a chronic inflammatory disease mainly affecting the spine and sacroiliac joints. There are two subtypes: non-radiographic, with no visible changes on X-ray, and radiographic, formerly called ankylosing spondylitis, which shows definite sacroiliitis on X-ray. Symptoms and management are largely similar between forms.

What is inflammatory back pain and how is it recognized?

Inflammatory back pain tends to be worse at rest, improves with exercise, and often wakes people in the second half of the night. It is recognized using five features: onset before age 40, gradual onset, improvement with exercise, no improvement with rest, and night pain. Having any four features identifies inflammatory back pain with 80% sensitivity and 74% specificity.

What do HLA-B27 blood test results mean for diagnosing axial spondyloarthritis?

HLA-B27 is the main genetic risk factor for axial spondyloarthritis. In a worldwide study, 65–89% of patients tested positive, depending on region, compared with about 6–8% of the general population in Europe and North America. A positive result meaningfully raises the chance of disease but is not a diagnosis by itself, since many HLA-B27-positive people never develop it.

Can an MRI alone confirm axial spondyloarthritis?

No. MRI findings must be interpreted with clinical and laboratory information. Bone marrow edema, the key finding, also appears in healthy people, runners, and postpartum women. In one study, 23% of healthy volunteers had an MRI considered positive for sacroiliitis. Other causes of bone marrow edema, especially mechanical stress, must always be considered, and erosions are usually absent in healthy athletes.

What should I expect during a diagnostic evaluation for axial spondyloarthritis?

Your doctor will consider your age, symptoms, physical examination, blood tests for CRP and HLA-B27, and imaging. A history of inflammatory back pain, arthritis, psoriasis, inflammatory bowel disease, uveitis, family history, and response to NSAIDs helps build a pattern. The doctor will also look for other causes of back pain. A diagnosis is a medical judgment integrating all these factors, not any single test.

Why might classification criteria not be used to diagnose my condition?

Classification criteria are designed for research, not for individual patient care. Using them as diagnostic tests misclassifies too many patients. In a meta-analysis of 4,990 patients, sensitivity was 82% and specificity 87%, meaning about 18 in 100 true cases are missed and 13 in 100 non-cases are falsely labeled. Real diagnosis requires clinical reasoning and excluding other causes.

When should someone with suspected axial spondyloarthritis seek a second opinion about the diagnosis?

Diagnosis requires recognizing a pattern across history, exam, blood tests, and imaging; no single feature is enough. A second opinion is important if the diagnosis rests only on research classification criteria, a simple count of features, or imaging findings alone, since these approaches misclassify patients. MRI findings can appear in healthy people and athletes, and many patients do not fit a typical picture. If back pain started after age 45, or no inflammatory changes are seen, diagnostic uncertainty remains. Diagnostic Detectives Network provides independent expert second opinions.

Source Information

Original article title: Challenges in the diagnosis of axial spondyloarthritis

Journal: Best Practice & Research Clinical Rheumatology, Volume 37 (2023), Article 101871

DOI: https://doi.org/10.1016/j.berh.2023.101871

Access: © 2023 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

This patient-friendly article is based on peer-reviewed research. It is provided for educational purposes and does not replace individual medical advice. Anyone experiencing chronic back pain should discuss their symptoms with a qualified physician.