Ankylosing spondylitis (AS) is a chronic inflammatory disease that primarily affects the spine and sacroiliac joints, where the spine connects to the pelvis. It belongs to a family of related conditions called spondyloarthritis. Over time, persistent inflammation can cause new bone to form in the spine, eventually leading to sections of vertebrae fusing together. This fusion reduces spinal flexibility and, in advanced cases, may result in a stooped or hunched posture.
AS typically develops in late adolescence or early adulthood, with most people experiencing symptoms before age 45. When inflammation affects the joints where the ribs connect to the spine, it can restrict chest expansion and make deep breathing difficult. Early diagnosis and treatment are essential for managing symptoms, maintaining mobility, and slowing disease progression.
Ankylosing spondylitis falls within a broader category called axial spondyloarthritis (axSpA), which refers to inflammatory conditions that primarily affect the spine and sacroiliac joints. AxSpA is classified into two types based on whether structural damage is visible on imaging:
Both forms can cause significant pain and stiffness, and nr-axSpA may progress to radiographic AS over time. Early diagnosis of either type allows for timely treatment that can help manage symptoms and slow disease progression.
Symptoms often come and go in cycles of flares and remission. Because early symptoms can be subtle and overlap with other conditions, AS is frequently misdiagnosed or delayed for years. If you experience persistent back pain lasting more than three months, especially if it began before age 45 and improves with activity, consult a rheumatologist for evaluation.
Ankylosing spondylitis symptoms typically develop gradually over weeks or months rather than appearing suddenly. Many people first notice symptoms in their late teens or twenties, though the condition can be difficult to recognize early because back pain is so common.
Diagnosing ankylosing spondylitis can be challenging because symptoms develop gradually and often resemble other causes of back pain. Your rheumatologist will use a combination of clinical evaluation, imaging, and lab work to reach an accurate diagnosis.
During your visit, your provider will assess your spinal mobility by asking you to bend and move in different directions. They may try to reproduce your pain by pressing on the pelvis or positioning your legs to stress the sacroiliac joints. You may also be asked to take deep breaths to evaluate whether chest expansion is limited, which can indicate rib involvement.
X-rays can reveal changes to the sacroiliac joints and spine that are characteristic of AS, including joint erosion or fusion. However, these changes may take years to appear. MRI is often used to detect inflammation earlier in the disease process, before structural damage becomes visible on X-ray, making it especially valuable for diagnosing non-radiographic axial spondyloarthritis.
There is no single blood test that confirms AS, but certain tests can support the diagnosis. The HLA-B27 genetic marker is present in a majority of people with AS, though having it does not guarantee you will develop the condition. Blood tests measuring inflammation levels, such as C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR), can also help your provider assess disease activity.
There is no cure for ankylosing spondylitis, but effective treatments can relieve pain and stiffness, maintain mobility, and prevent or delay spinal complications. The earlier AS is diagnosed, the sooner treatment can begin to help avoid irreversible damage. Your rheumatologist will work with you to develop a personalized treatment plan based on your symptoms and disease activity.
