Non-radiographic axial spondyloarthritis (nr-AxSpA) and ankylosing spondylitis (AS) are two forms of a chronic inflammatory condition known as axial spondyloarthritis (AxSpA). These conditions are considered to be part of the same disease spectrum, with AS representing a more advanced stage where structural changes are visible on X-rays. Understanding their distinctions and similarities is helpful for those navigating these diagnoses.
Understanding Axial Spondyloarthritis
Axial spondyloarthritis (AxSpA) is a category of inflammatory arthritis that primarily affects the axial skeleton, which includes the spine, pelvis, and chest. This condition is characterized by persistent inflammation, particularly in the sacroiliac (SI) joints where the spine connects to the pelvis, and along the spine itself. Inflammation can also occur at entheses, which are the sites where tendons and ligaments attach to bone.
AxSpA is a chronic, progressive disease that may worsen over time without appropriate management. Beyond the spine, AxSpA can also affect other areas of the body, including peripheral joints, eyes, skin, or the gastrointestinal tract. The inflammatory nature of the disease is mediated by the immune system, though its exact causes are not fully understood.
The Defining Difference: Imaging
The primary distinction between non-radiographic axial spondyloarthritis (nr-AxSpA) and ankylosing spondylitis (AS) lies in the presence or absence of visible structural damage on conventional X-rays of the sacroiliac (SI) joints. This imaging difference helps classify the stage of the disease.
Ankylosing spondylitis (AS), also known as radiographic axial spondyloarthritis, is diagnosed when X-rays of the SI joints show clear, definitive structural changes. These changes can include erosions, sclerosis (hardening of bone), joint space narrowing or widening, and in advanced cases, fusion of the joints. The modified New York Criteria define what constitutes “definitive damage” on SI joint X-rays for an AS diagnosis.
In contrast, non-radiographic axial spondyloarthritis (nr-AxSpA) involves similar symptoms and inflammation, but without these visible structural changes on standard X-rays. While X-rays may appear normal, inflammation in the SI joints might be detectable using more sensitive imaging techniques, such as magnetic resonance imaging (MRI). MRI can reveal active inflammation, like bone marrow edema, even before permanent bone damage occurs.
Shared Symptoms and Clinical Presentation
Despite the differences in radiographic findings, individuals with nr-AxSpA and AS often experience a similar range of symptoms and disease burden.
Both conditions present with inflammatory back pain, which develops gradually over weeks or months. This pain is worse with rest, especially at night or in the early morning, and improves with physical activity.
Patients report morning stiffness that lasts for an extended period after waking. The pain can manifest in the lower back, hips, and buttocks, sometimes alternating sides.
Beyond axial symptoms, both nr-AxSpA and AS can involve extra-articular manifestations. These include uveitis (inflammation of the eye), psoriasis (a skin condition with red patches), and inflammatory bowel disease (such as Crohn’s disease or ulcerative colitis).
Diagnosis and Disease Progression
Diagnosing axial spondyloarthritis, whether nr-AxSpA or AS, involves a comprehensive assessment that combines clinical symptoms, physical examination, and specific tests.
A rheumatologist, a specialist in joint and musculoskeletal conditions, leads this diagnostic process. The doctor will inquire about symptoms, medical history, and family history of similar conditions.
Physical examination assesses for tenderness, swelling, and limitations in spinal mobility, particularly in the back, pelvis, and hips.
Blood tests may be ordered to check for inflammatory markers like C-reactive protein (CRP), which can be elevated in active inflammation, and for the presence of the HLA-B27 genetic marker, which is strongly associated with AxSpA but not definitive for diagnosis.
Imaging tests are also used; MRI can detect active inflammation in the SI joints in nr-AxSpA even when X-rays are clear.
Some individuals with nr-AxSpA may progress to AS over time. Studies indicate that progression occurs in approximately 5% to 30% of cases over 2 to 30 years. Factors associated with a higher likelihood of progression include male sex, elevated C-reactive protein levels, and significant inflammation visible on SI joint MRI. However, not all individuals with nr-AxSpA will develop AS, and some may remain in the non-radiographic stage indefinitely.
Treatment and Management Approaches
Treatment strategies for both non-radiographic axial spondyloarthritis (nr-AxSpA) and ankylosing spondylitis (AS) share common goals: to reduce inflammation, alleviate pain, improve mobility, and prevent further structural damage. The therapeutic approaches are largely similar because they target the underlying inflammatory processes.
Non-steroidal anti-inflammatory drugs (NSAIDs) are the first-line treatment for both conditions. These medications help reduce pain and stiffness by lowering inflammation. If one NSAID is not effective, a different type may be tried, and they are taken regularly rather than just when pain flares.
For individuals with more severe or persistent disease that does not respond adequately to NSAIDs, biologic medications are prescribed. These advanced therapies, such as TNF inhibitors (e.g., adalimumab) and IL-17 inhibitors (e.g., secukinumab), target specific molecules in the immune system to reduce inflammation. Several biologics are approved for nr-AxSpA with objective inflammation.
Physical therapy and regular exercise are important components of managing both nr-AxSpA and AS. Exercise helps maintain spinal mobility, flexibility, and good posture, and can improve fatigue and overall quality of life. A physical therapist can develop an individualized exercise program that may include stretches, mobility exercises, and strengthening routines. Other supportive measures include applying heat or cold to affected joints, and stress reduction techniques, as stress can exacerbate symptoms. In select severe cases, particularly with significant spinal deformity or hip involvement, surgery might be considered.