Axial spondyloarthritis (AxSpA) causes inflammation in the spine and/or pelvis that typically brings on inflammatory back pain. AxSpA is a broad category that includes people with and without characteristic inflammatory changes of the sacroiliac joints (the joints between the pelvis and the sacrum or base of the spine) seen on X-ray.
Doctors classify people as having a certain type of axial spondyloarthritis:
- Radiographic AxSpA with characteristic changes seen on X-ray.
- Nonradiographic AxSpA without characteristic changes seen on X-ray.
Almost all people with ankylosing spondylitis fit into the category of radiographic AxSpA. People with reactive arthritis, enteropathic arthritis, undifferentiated spondyloarthritis, and psoriatic arthritis may fit into the category of either radiographic AxSpA or nonradiographic AxSpA.