Some people with nr-axSpA progress to developing AS, although many do not. Studies have found rates of progression from nr-axSpA to AS ranging from 5% to 30% over 2 to 30 years. In general, male sex, a high level of C-reactive protein in the blood, and a high degree of inflammation as seen on an SI joint MRI are risk factors for progression from nr-axSpA to AS.
The primary feature of nr-axSpA is the involvement of the sacroiliac (SI) joints, which are located at the base of the spine, where the spine joins the pelvis. Nr-axSpA can also cause inflammation, pain, and stiffness in other areas of the body such as the neck, shoulders, hips, ribs, heels, and joints of the arms and legs. Inflammation can also impact the eyes (causing iritis or uveitis), the skin (causing psoriasis), and the gut (causing intestinal pain and other problems).
One key takeaway from recent research is that pain, stiffness, and other symptoms are as severe in people with nr-axSpA as they are in those with ankylosing spondylitis.