Axial spondyloarthritis (axSpA) is a chronic inflammatory disease that primarily affects the spine and the sacroiliac joints, where the lower spine connects to the pelvis. Unlike the wear-and-tear damage of osteoarthritis, this condition is driven by an overactive immune system that triggers inflammation in and around the joints of the back. It typically begins before age 40 and is one of the most common causes of chronic back pain in younger adults.
Two Forms of the Same Disease
Axial spondyloarthritis exists on a spectrum. At one end is the non-radiographic form (nr-axSpA), where inflammation is present but hasn’t yet caused visible structural damage on standard X-rays. At the other end is the radiographic form (r-axSpA), historically known as ankylosing spondylitis, where X-rays show clear damage to the sacroiliac joints. The distinction between the two comes down to what’s visible on imaging, not how severe the symptoms feel. People with the non-radiographic form can experience the same level of pain and stiffness as those with ankylosing spondylitis.
About 16% of people initially diagnosed with non-radiographic axSpA progress to the radiographic form within five years, based on a large multicountry study. Some estimates put that range as high as 40% over a decade, depending on risk factors. This doesn’t mean everyone progresses. Many people remain in the non-radiographic stage indefinitely, and early treatment may slow or prevent structural damage.
How It Feels Different From Ordinary Back Pain
The hallmark symptom is inflammatory back pain, which behaves very differently from the mechanical back pain most people experience. Rheumatologists use five key features to distinguish the two:
- It improves with movement. Getting up and exercising tends to reduce the pain, while sitting or lying still makes it worse.
- It wakes you at night. Pain during the second half of the night is characteristic, often forcing people out of bed.
- It comes on gradually. There’s no single injury or event that starts it. The pain builds slowly over weeks or months.
- It starts before age 40. Most people notice symptoms in their 20s or 30s.
- Rest doesn’t help. Unlike a pulled muscle or herniated disc, resting makes inflammatory back pain worse, not better.
When at least four of these five features are present, the pattern strongly points toward inflammatory back pain. Morning stiffness lasting 30 minutes or more is another common complaint. Some people also develop pain in the buttocks that alternates from side to side, reflecting inflammation shifting between the two sacroiliac joints.
How It’s Diagnosed
Diagnosing axSpA is notoriously slow. Studies have found average delays of seven to ten years between symptom onset and diagnosis, partly because back pain is so common and inflammatory back pain is often mistaken for a sports injury or disc problem.
Doctors typically start with blood tests looking for markers of inflammation and the HLA-B27 gene, which is present in a large proportion of people with the condition. But the gene alone isn’t diagnostic. Many people carry HLA-B27 and never develop the disease.
Imaging plays a central role. Standard X-rays of the sacroiliac joints can confirm ankylosing spondylitis if they show characteristic erosion or fusion. For the non-radiographic form, MRI is the key tool. The defining finding is bone marrow edema (essentially, swelling inside the bone) in the sacroiliac joints, which signals active inflammation even when X-rays look normal. The presence of this bone swelling on MRI, in the right clinical context, is considered the essential observation for identifying active sacroiliitis when X-ray changes are absent or uncertain.
Beyond the Back: Related Conditions
Axial spondyloarthritis is more than a spine disease. The same immune dysfunction that attacks the joints can cause inflammation in other parts of the body, and these so-called extra-articular manifestations are common enough that doctors actively screen for them.
Uveitis, an inflammation of the eye that causes redness, pain, and light sensitivity, is among the most frequent. It requires prompt treatment to prevent vision problems. Psoriasis, the skin condition marked by red, scaly patches, also occurs at higher rates. And inflammatory bowel disease (IBD), which includes Crohn’s disease and ulcerative colitis, affects roughly 9% of people with axSpA. In one large study, many of these IBD cases had gone undiagnosed, meaning gut symptoms in someone with axSpA deserve attention even if they seem unrelated.
Enthesitis, or inflammation where tendons and ligaments attach to bone, is another common feature. This can show up as heel pain (at the Achilles tendon) or tenderness along the rib cage.
Treatment: What Works
Anti-inflammatory medications are the first line of treatment and remain the backbone of symptom management. For many people, a consistent regimen of these medications significantly reduces pain and stiffness. But when standard anti-inflammatories aren’t enough, several classes of more targeted therapies are available.
Biologic medications that block specific immune signals have transformed outcomes for people with moderate to severe disease. Two main classes are used: one targets a protein called TNF-alpha, which drives inflammation throughout the body, and the other targets interleukin-17, a different immune messenger involved in the inflammatory cascade. Both have been shown in large clinical trials to suppress inflammation and relieve symptoms in both forms of axSpA.
A newer class of oral medications works by blocking enzymes called JAK proteins, which sit inside cells and relay inflammatory signals. Two of these medications have received approval from both the FDA and European regulators for active ankylosing spondylitis, and one has also been approved specifically for the non-radiographic form. These are typically prescribed when someone hasn’t responded well to other treatments.
The Role of Exercise
Exercise isn’t just a supplement to medication for axSpA. It’s considered a core part of treatment. European treatment guidelines recommend four types of exercise: aerobic activity, strength training, flexibility work, and balance or coordination exercises.
Traditionally, hydrotherapy (pool-based exercise) and stretching have been the go-to recommendations, but recent research suggests strength training is an underused option that deserves more attention. Large, multicenter studies have shown that high-intensity exercise can improve disease activity scores and also reduce cardiovascular risk, which matters because chronic inflammation raises heart disease risk over time.
The practical reality is that exercising with a stiff, painful back feels counterintuitive. But because inflammatory back pain specifically improves with movement, most people find that consistent exercise reduces their baseline pain and preserves spinal mobility. Working with a physical therapist who understands axSpA can help you find the right intensity and type of movement, though specific guidelines on exactly how much exercise is needed to produce benefit are still being refined.
Who Gets It
Axial spondyloarthritis has historically been viewed as a disease that predominantly affects young men, but that picture is changing. Prevalence data from the U.S. shows rates rising from about 40 to 90 per 100,000 people between 2006 and 2016. In the UK, prevalence climbed from 130 to 180 per 100,000 between 1998 and 2017. These increases likely reflect better awareness and diagnosis rather than a true surge in new cases.
Notably, the increase has been most pronounced among women and older adults, groups that were historically underdiagnosed. Women with axSpA tend to present with more widespread pain and fatigue and less dramatic X-ray findings, which may have led to decades of missed diagnoses. The disease is not rare, and it’s not limited to any single demographic profile.