Non-radiographic axial spondyloarthritis (nr-axSpA) is a chronic, inflammatory form of arthritis that primarily affects the spine and the joints connecting the spine to the pelvis, known as the sacroiliac joints. This condition is part of a larger family of diseases called spondyloarthritis, where inflammation is driven by an overactive immune system mistakenly attacking healthy tissue. Unlike mechanical back pain, which is typically caused by structural issues like strains or disc problems, nr-axSpA is characterized by persistent back pain resulting from this underlying chronic inflammation. The condition often causes significant stiffness and pain that can severely impact a person’s quality of life and ability to function.
Placing nr-axSpA within the AxSpA Spectrum
Axial Spondyloarthritis (AxSpA) is the umbrella term for inflammatory diseases that affect the axial skeleton, and it comprises two main subtypes: non-radiographic AxSpA (nr-axSpA) and radiographic AxSpA, which is also known as Ankylosing Spondylitis (AS). Both conditions share nearly identical symptoms, disease activity, and underlying inflammatory processes. The primary distinction lies solely in what is visible on conventional imaging, specifically X-rays of the sacroiliac joints.
Patients diagnosed with nr-axSpA have not yet developed the irreversible structural damage, such as joint fusion or significant erosions, visible on a standard X-ray image. This lack of definitive X-ray changes is what gives the condition its “non-radiographic” designation. Conversely, when the inflammatory process has advanced enough to cause unequivocal damage to the sacroiliac joints visible on X-ray, the diagnosis changes to Ankylosing Spondylitis.
AxSpA views these two conditions as existing along a continuum of the same disease. Nr-axSpA generally represents the earlier stage of disease progression. However, nr-axSpA is not simply early AS, as a significant number of patients may never develop the X-ray changes needed for the AS diagnosis.
Recognizing Inflammatory Symptoms and Genetic Risk Factors
The symptom of nr-axSpA is inflammatory back pain, which has a specific pattern that helps distinguish it from more common mechanical pain. This pain typically has an insidious onset, developing gradually, and often begins before the age of 45. A defining feature is that the pain and stiffness improve with physical activity and exercise, but become noticeably worse after periods of rest or immobility.
Patients commonly report being woken up by pain during the second half of the night, often forcing them to get up and move around for relief. The stiffness is usually most severe in the morning and can last for more than 30 minutes. Nr-axSpA can also cause inflammation in other areas of the body, known as extra-spinal manifestations.
These extra-spinal manifestations include:
- Uveitis, which is inflammation of the eye.
- Enthesitis, which is inflammation where tendons or ligaments attach to the bone, such as in the heel or Achilles tendon.
- Inflammatory bowel disease (IBD), such as Crohn’s disease or ulcerative colitis.
- The skin condition psoriasis.
The primary genetic risk factor associated with this disease spectrum is the Human Leukocyte Antigen B27 (HLA-B27) gene. While the presence of HLA-B27 suggests a genetic predisposition, it is not a diagnostic confirmation, as many healthy people also carry the gene.
The Diagnostic Process
Diagnosing nr-axSpA requires evaluation by a rheumatologist, as no single test can definitively confirm the condition. Diagnosis begins with assessing the patient’s symptoms and medical history to confirm inflammatory back pain. A physical examination is also performed to check for tenderness in the sacroiliac joints and to measure limitations in spinal mobility.
The distinction between nr-axSpA and AS relies heavily on imaging tests. Conventional X-rays are used to rule out the advanced structural damage that defines AS. In the absence of definitive X-ray changes, Magnetic Resonance Imaging (MRI) becomes the most important tool for diagnosis.
The MRI allows the rheumatologist to visualize active inflammation in the sacroiliac joints and spine, which appears as bone marrow edema (BME). This active inflammation provides objective evidence of the disease even before structural damage is visible on X-ray. Blood tests, including the HLA-B27 test and measurements of inflammatory markers like C-reactive protein (CRP), are used to support the clinical picture, but they are not conclusive on their own.
Managing nr-axSpA and Long-Term Outlook
The goal of managing nr-axSpA is to control inflammation, relieve pain, and maintain spinal mobility and function. Treatment typically follows a tiered approach, beginning with non-steroidal anti-inflammatory drugs (NSAIDs). Consistent use of NSAIDs is often effective at reducing pain and stiffness caused by the inflammation.
If symptoms persist despite NSAIDs, the next step involves using Biologic Disease-Modifying Anti-Rheumatic Drugs (bDMARDs), most commonly Tumor Necrosis Factor (TNF) inhibitors. These medications target specific proteins in the immune system to reduce systemic inflammation. Non-pharmacological interventions are also important, with regular physical therapy and exercise recommended to help maintain flexibility and posture.
The long-term outlook for nr-axSpA varies considerably among individuals. While the disease burden and impact on quality of life can be comparable to that of AS, not all patients will progress to the radiographic stage. Studies suggest that between 5% and 30% of patients may eventually progress to AS over many years.
Progression and Monitoring
Factors such as an elevated CRP level or the presence of bone marrow edema on MRI at diagnosis suggest a higher likelihood of future progression. Regular monitoring by a rheumatologist is necessary to assess disease activity and adjust the treatment strategy as needed.