By rheumatologists Patricia Remalante-Rayco, MD and Dr. Nigil Haroon, MD, PhD
Axial spondyloarthritis (axSpA) is characterized by inflammation of the spine and the sacroiliac (SI) joints, which connect the lower end of the spine to the hip bones. The knees, ankles, hips, and wrists may also be affected in some patients. This inflammation occurs because the immune system is tricked into attacking one’s own body for reasons that remain unclear, although it seems that genes including (but not limited to) HLA-B27, and environmental factors, have a role to play.
The typical age of axSpA onset is before 45; patients with axSpA often first experience low back pain and stiffness in their late adolescence or twenties. The pain can wake you up at night and make it difficult for you to get up and move in the morning. The pain associated with axSpA is inflammatory back pain, which doesn’t go away when you rest. Instead, it improves when you stretch, exercise, or move around. For some patients, the inflammation causing these symptoms may lead to varying degrees of spine fusion, as seen on x-rays. When axSpA is associated with abnormal x-rays, it is called ankylosing spondylitis (AS). AS is also called radiographic axSpA (r-axSpA) because plain radiographs (x-rays) will show damage in the sacroiliac joints.
Did you know? Iritis (inflammation of the eye), gastrointestinal conditions (such as Crohn’s disease and ulcerative colitis), and dactylitis (inflammation or swelling of an entire finger or toe) can also occur in axSpA.
However, not all people with axSpA, despite having the same inflammation and symptoms described above, will have visible changes on x-rays. This may be because the disease is progressing more slowly, or manifests predominantly as inflammation with no bone changes. In these cases, the diagnosis is non-radiographic axSpA (nr-axSpA).
AS and nr-axSpA are thus part of the same axSpA disease spectrum and present with many of the same symptoms. The main difference is that those with nr-axSpA don’t show bone changes on x-rays, which can result in diagnostic delays that are even longer than those in AS.
Did you know? X-ray changes may eventually develop over years in some with nr-axSpA, but not in everyone. Therefore, not all nr-axSpA patients progress to AS. 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.
Even though damage to joints may not be visible on x-ray, active inflammation in those with nr-axSpA can be captured early on with the help of MRI, making earlier diagnosis possible. With early diagnosis, the inflammation can be targeted before it can lead to bone fusion and reduced mobility.
Yet while the MRI is a very helpful test, it isn’t perfect. MRI may show changes suggestive of inflammation in some individuals with either no pain or with mechanical causes of back pain. Similarly, it may not always show definitive changes related to axSpA even in those who have the condition.
This is why doctors don’t rely on a single test to diagnose axSpA, but rather consider a combination of a person’s medical history, physical examination, blood tests, x-rays, and if required, genetic testing and MRI. Even with a negative MRI, patients may be diagnosed with nr-axSpA if the clinical suspicion of an experienced doctor is sufficiently strong.
Did you know? The signs and symptoms of axSpA, including pain, fatigue, morning stiffness, localized tenderness and soreness, do not depend on SI joint damage visible on an x-ray. Several studies have shown that the disease burden in nr-axSpA is as severe as that in AS.
An early diagnosis of nr-axSpA is vital for the best health outcomes. The goal is to detect the disease and begin treatment before it causes long-term complications. It has been shown that patients who started treatment early in the course of their disease responded better to treatment, with improved control of pain, stiffness, and functioning. Evidence also suggests that early control of inflammation may slow the progression of bone damage.
Did you know? The male to female ratio in AS is widely believed to be somewhere around 3:1 or 2:1, whereas in nr-axSpA it is close to 1:1. A person’s sex can affect the location of initial pain in axSpA. For some women, the neck and peripheral joints are affected first, whereas in men it is much more likely to be the lower back.
If you suspect that you have nr-axSpA, there are things you and your doctor can do to help manage it. A holistic treatment plan that includes exercise, good nutrition, medication if needed, and other lifestyle changes can control symptoms and improve overall outcomes.
Did you know? On October 1st, 2020, the CDC gave nr-axSpA its own diagnostic code, M46.8. SAA advocated for this change, which boosts recognition of nr-axSpA among clinicians and researchers and makes it easier for the medical community to study, diagnose, track, and develop treatments for the condition.
Dr. Patricia Remalante-Rayco MD
Clinical Fellow, Spondylitis Program
University Health Network, Toronto, ON.
Dr. Nigil Haroon MD, PhD, DM, FRCPC
Co-Director, Spondylitis Program, University Health Network
Associate Professor of Medicine and Rheumatology
University of Toronto, Toronto, ON.