Ankylosing Spondylitis: Why You Might Be Getting the Wrong MRI (And What to Ask For Instead)
If you’ve been dealing with unexplained lower back pain for months — or even years — and nothing seems to explain it, you’re not alone. Ankylosing spondylitis (AS) is one of the most commonly missed or delayed diagnoses in rheumatology. And a big reason why? Patients often get the wrong imaging test.
At Chicago Arthritis, our team specializes in identifying inflammatory arthritis conditions like ankylosing spondylitis early — before they cause lasting joint damage. Here’s what every patient should know.
What Is Ankylosing Spondylitis?
Ankylosing spondylitis is a type of inflammatory arthritis that primarily affects the spine and the sacroiliac (SI) joints — the joints connecting your lower spine to your pelvis. Left untreated, it can lead to:
- Chronic pain and stiffness
- Reduced mobility and function
- Long-term structural damage to the spine
- Complications involving the heart, lungs, eyes, gut, and skin
The tricky part? AS often starts quietly, with symptoms that get brushed off as “normal” back pain or wear and tear.
The #1 Sign Doctors (and Patients) Miss: Inflammatory Back Pain
Not all back pain is created equal. There’s a specific pattern that should raise a red flag for ankylosing spondylitis:
Classic Inflammatory Back Pain Symptoms
- Pain that’s worse at rest, especially first thing in the morning
- Pain that improves with activity or movement
- Morning stiffness lasting more than one hour — not just a few minutes
- Symptoms that began before age 30 (though not always)
This is the opposite of typical mechanical or “wear and tear” back pain, which usually gets worse with activity and better with rest.
Why Family History Matters
Autoimmune conditions tend to run in families. If you have a relative with:
- Rheumatoid arthritis
- Ankylosing spondylitis
- Crohn’s disease or ulcerative colitis
- Psoriasis or psoriatic arthritis
…your risk of developing an inflammatory condition like AS is higher. This history alone can be an important clue that helps guide diagnosis, even before lab work or imaging is done.
The Imaging Mistake That Delays Diagnosis
Here’s where things often go wrong.
When someone has lower back pain, doctors commonly order an MRI of the lumbar spine. That test is useful for identifying disc problems or structural spine issues — but it has a major blind spot.
Why a Lumbar Spine MRI Isn’t Enough
An MRI of the lumbar spine only captures the top portion of the SI joints. It typically misses the next three to five inches of the joint — which is exactly where the earliest signs of ankylosing spondylitis, like inflammation and early bone changes, tend to show up.
The Correct Test: MRI of the Pelvis
To properly evaluate the SI joints for inflammation (called sacroiliitis) or early damage, an MRI of the pelvis is needed. This is the imaging study that can catch ankylosing spondylitis years before it would ever show up on an X-ray.
Why not just get an X-ray? X-rays can take years to show changes from AS, since they only detect more advanced, chronic damage. By the time X-ray changes appear, significant progression may have already occurred.
Lab Testing: What the HLA-B27 Test Really Means
Along with imaging, your doctor may order:
- Inflammation markers (such as ESR or CRP) — though these aren’t always elevated, especially early on
- HLA-B27 genetic testing — a blood test linked to a higher likelihood of spondyloarthropathy and ankylosing spondylitis
A positive HLA-B27 result increases suspicion for AS, but a negative result doesn’t rule it out. Diagnosis is based on the full picture: symptoms, family history, labs, and imaging together.
Why Early Diagnosis Makes Such a Big Difference
It was once believed that ankylosing spondylitis took decades to cause noticeable damage. We now know that inflammation — and even early bone erosion — can begin much sooner than previously thought.
Catching AS early allows for treatment that can:
- Reduce pain and stiffness
- Preserve mobility and function
- Slow or prevent long-term structural damage
- Lower the risk of related complications affecting the heart, lungs, eyes, and gut
When Should You See a Rheumatologist?
If you’re experiencing classic inflammatory back pain symptoms — especially alongside a family history of autoimmune disease — don’t wait for years of unexplained pain to pass before seeking answers.
A rheumatology specialist can help determine whether your symptoms, labs, and imaging point toward ankylosing spondylitis or another form of inflammatory arthritis, and build a personalized treatment plan that may include medication management, physical therapy, or regenerative medicine approaches like PRP therapy for joint support.
Take the Next Step Toward Answers
You don’t have to keep guessing about the source of your back pain. Whether you’re dealing with joint pain, suspected autoimmune disease, or chronic inflammation that hasn’t been explained, getting the right diagnostic workup matters.
Visit ChicagoArthritis.com to learn more or schedule a consultation with our rheumatology and regenerative medicine team. Early diagnosis can change the entire course of your treatment — and your quality of life.
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