Axial spondyloarthritis (axSpA) is a chronic inflammatory disease that primarily attacks the spine and the joints where the spine meets the pelvis, called the sacroiliac joints. It typically begins before age 40, and the average person waits 7.4 years from first symptoms to diagnosis, according to a 2025 multinational survey spanning 27 countries. That delay matters because early treatment can slow or prevent permanent damage to the spine.
Two Forms of the Same Disease
Axial spondyloarthritis exists on a spectrum, divided into two categories based on what shows up on a standard X-ray. Radiographic axSpA, historically called ankylosing spondylitis, is defined by visible structural damage to the sacroiliac joints on X-ray: erosions, hardening of bone, or fusion. Non-radiographic axSpA (nr-axSpA) describes patients with the same symptoms and inflammatory process, but whose X-rays still look normal.
This distinction matters less than it sounds. The underlying disease is the same. In non-radiographic cases, MRI often reveals active inflammation in the form of bone marrow swelling in the sacroiliac joints, even though X-rays appear clean. Over years, a proportion of people with nr-axSpA will develop the visible joint damage that reclassifies them as radiographic. The inflammation comes first; the structural damage follows later, sometimes by a decade or more.
How Inflammatory Back Pain Feels Different
The hallmark symptom is inflammatory back pain, which behaves almost opposite to the kind of back pain most people experience from a muscle strain or disc problem. Mechanical back pain gets worse with activity and better with rest. Inflammatory back pain does the reverse: it improves with movement and exercise but worsens with prolonged rest. People often describe the worst stiffness first thing in the morning, sometimes lasting 30 minutes or longer, and pain that wakes them in the second half of the night. Getting up and moving around relieves it.
The pain typically starts gradually rather than after a specific injury, centers in the lower back and buttocks, and persists for three months or more. It usually begins before age 40. If your back pain fits this pattern, it’s worth bringing up with a doctor, because the overlap with “regular” back pain is one of the main reasons diagnosis takes so long.
What Causes It
Axial spondyloarthritis is driven by an overactive immune system that targets the places where ligaments and tendons attach to bone, particularly in the spine and pelvis. Two key immune signaling molecules fuel the process. One triggers widespread inflammation in and around the joints. The other contributes to both inflammation and an abnormal bone-growth response, where the body lays down new bone in places it shouldn’t, gradually bridging the gaps between vertebrae.
Genetics play a major role. Roughly 90% to 95% of Caucasian patients carry a gene variant called HLA-B27, compared to just 6% to 8% of the general population. Carrying HLA-B27 doesn’t mean you’ll develop axSpA (most carriers never do), but it significantly increases susceptibility. The gene is thought to influence how the immune system processes certain proteins, though the exact mechanism is still being worked out. Family history is one of the strongest risk factors.
How It’s Diagnosed
There is no single blood test that confirms axSpA. Diagnosis relies on a combination of symptoms, imaging, blood markers, and clinical judgment. Doctors typically look for inflammatory back pain lasting three months or more in someone under 45, then layer on supporting evidence: HLA-B27 status, blood markers of inflammation, and imaging results.
MRI of the sacroiliac joints is the most sensitive imaging tool for early disease. The key finding is bone marrow swelling (edema) adjacent to the joint surfaces. To count as significant, this swelling needs to be either at least one centimeter deep and visible on two consecutive MRI slices, or present in at least two separate locations on the same image. Standard X-rays can confirm later-stage disease but often miss the first several years of inflammation entirely.
Importantly, no single finding seals the diagnosis. MRI changes alone aren’t enough, and some patients are diagnosed based on clinical features and HLA-B27 positivity even without clear MRI inflammation. The full picture matters more than any individual test.
Beyond the Spine
Axial spondyloarthritis isn’t limited to the back. Many people develop symptoms in other parts of the body, sometimes before back pain even begins. The most common are inflammatory bowel disease (affecting roughly 18-19% of patients in some studies), anterior uveitis (a painful inflammation of the eye, around 12-13%), and psoriasis (about 2%). Peripheral joint pain in the hips, shoulders, or knees is also common.
Uveitis typically causes sudden eye redness, pain, light sensitivity, and blurred vision in one eye. It tends to come in flares and needs prompt treatment to prevent vision damage. If you have axSpA and develop a red, painful eye, it warrants urgent evaluation.
First-Line Treatment: Anti-Inflammatory Medications
Anti-inflammatory drugs (NSAIDs) are the starting point for treatment and remain the backbone of symptom management. For many people, a consistent NSAID regimen significantly reduces pain and stiffness. Treatment guidelines recommend trying at least two different NSAIDs at full doses, each for a minimum of one month, before concluding they aren’t working well enough. Some people respond much better to one NSAID than another, so switching is worthwhile.
Physical therapy and regular exercise are equally important and not optional add-ons. Stretching, strengthening, and aerobic exercise help maintain spinal mobility, reduce stiffness, and improve long-term outcomes. Many patients find that daily movement is the single most effective tool for managing day-to-day symptoms.
Biologic and Targeted Therapies
When NSAIDs aren’t enough, the next step is biologic therapy. These are medications that block the specific immune molecules driving inflammation. The main categories include drugs that block the inflammation-triggering molecule TNF (six different options are currently available), drugs targeting the IL-17 pathway involved in both inflammation and abnormal bone growth (three options), and a newer class called JAK inhibitors that work by interrupting immune signaling inside cells (two options).
These medications are given by injection or infusion and can produce significant improvement in pain, stiffness, and fatigue, often within the first few weeks. Not every medication is approved for both forms of the disease. Some JAK inhibitors and one TNF blocker are currently licensed only for the radiographic form. Your rheumatologist will match the choice to your specific situation, factoring in disease severity, other conditions you may have, and your preferences around injection frequency.
Long-Term Spinal Changes
The most serious long-term concern in axSpA is progressive stiffening and fusion of the spine. This happens when chronic inflammation triggers new bone growth between vertebrae (called syndesmophytes) and in the small facet joints at the back of the spine. Once bone bridges form between two vertebrae, those segments lose mobility permanently.
This process feeds on itself. Research shows that having bony bridges at one spinal level roughly triples the odds of the small joints at the same level fusing over the following two years. Conversely, fusion of those small joints nearly doubles the risk of new bony bridges developing nearby. The more segments involved, the higher the risk accelerates. Active inflammation in the vertebrae is one of the strongest predictors of future structural damage, which is a core argument for controlling inflammation early and aggressively.
Not everyone progresses to significant fusion. Risk factors include male sex, smoking, higher baseline inflammation levels, and already having structural damage at diagnosis. Sustained treatment with biologic therapies, combined with consistent exercise, offers the best current strategy for slowing this progression.