Non-Radiographic Axial Spondyloarthritis (nr-axSpA): a term used to describe a condition that produces back pain related to the sacroiliac joints and lower spine, the typical symptoms of a condition known as ankylosing spondylitis (AS), but without the changes seen on X-ray that characterize AS. AS is a chronic and multisystem inflammatory disorder that may involve any of the spine joints and usually shows abnormalities on X-rays of the spine. It is possible that nr-axSpA represents either an incomplete form of AS or is a milder form of AS. The cause of AS and nr-axSpA is not known, but both genetic and environmental factors may be involved in its development. For example, people with HLA-B27 genes are at increased risk for the disease, and AS is more common in people with relatives with AS. Induction of AS, nr-axSpA and other related AS diseases may be triggered by an immune response to bacterial infection such as Klebsiella.
The main symptom of nr-axSpA is chronic back pain that is worse late at night or early morning. The pain typically begins slowly in the teen or young adult years. Symptoms often improve after exercise. Some people with the condition develop uveitis (a form of eye inflammation).