Overview
Non-radiographic axial spondyloarthritis (nr-axSpA) is a chronic inflammatory condition primarily affecting the axial skeleton, characterized by inflammation of the sacroiliac joints and spine without the presence of radiographic evidence of ankylosing spondylitis (AS). It often precedes AS and can evolve into a radiographic form over time. Patients typically experience chronic back pain and stiffness, particularly in the morning or after inactivity, which significantly impacts quality of life. This condition predominantly affects young adults, with a slight male predominance. Understanding nr-axSpA is crucial in day-to-day practice for early diagnosis and intervention to prevent disease progression and manage symptoms effectively 1.Pathophysiology
The pathophysiology of nr-axSpA involves a complex interplay of genetic predisposition and environmental factors leading to chronic inflammation. HLA-B27 genetic marker is strongly associated with the disease, particularly in individuals who develop AS from nr-axSpA. At the molecular level, aberrant immune responses contribute to the activation of T-cells and the production of pro-inflammatory cytokines such as tumor necrosis factor (TNF)-α, interleukin (IL)-17, and IL-23. These cytokines promote inflammation and perpetuate the inflammatory cycle within the axial joints and entheses. The lack of radiographic changes in early stages suggests that structural damage may not yet be evident, but subclinical inflammation is present, leading to symptoms like pain and stiffness without visible joint damage 1.Epidemiology
Nr-axSpA has an estimated prevalence ranging from 0.5% to 1.5% in the general population, with a higher incidence observed in younger adults, typically between the ages of 17 and 40. Males are affected more frequently than females, with a male-to-female ratio often cited around 2:1 to 3:1. Geographic distribution shows no significant regional bias, but certain populations with higher prevalence of HLA-B27, such as those of Northern European descent, may exhibit increased incidence rates. Over time, trends indicate an increasing awareness and diagnosis due to better imaging techniques and clinical criteria, though the true incidence may have remained relatively stable 1.Clinical Presentation
Patients with nr-axSpA commonly present with chronic lower back pain and stiffness, often exacerbated by inactivity and relieved by physical activity. Morning stiffness lasting more than 30 minutes is a hallmark symptom. Other typical presentations include peripheral arthritis affecting large joints like the knees and ankles, enthesitis (inflammation at sites where tendons insert into bone), and dactylitis (sausage-like swelling of fingers or toes). Atypical features might include uveitis, psoriasis, and inflammatory bowel disease, especially in those with concomitant HLA-B27 positivity. Red-flag symptoms such as unexplained weight loss, fever, or significant neurological deficits should prompt urgent evaluation for complications or alternative diagnoses 1.Diagnosis
The diagnosis of nr-axSpA involves a comprehensive clinical evaluation supported by specific criteria and ancillary tests. Key diagnostic approaches include:Clinical Criteria: The Assessment of SpondyloArthritis International Society (ASAS) criteria for axial spondyloarthritis (axSpA) are widely used. These criteria require chronic back pain for more than 3 months and at least one of the following: elevated C-reactive protein (CRP) or erythrocyte sedimentation rate (ESR), good response to nonsteroidal anti-inflammatory drugs (NSAIDs), and/or evidence of inflammation on magnetic resonance imaging (MRI) of the sacroiliac joints or spine 1.
Imaging: Radiographs typically show no definitive signs of AS in early stages, but MRI and ultrasound can reveal early inflammatory changes and active synovitis.
Laboratory Tests: Elevated inflammatory markers (CRP > 10 mg/L or ESR > 20 mm/h) support the diagnosis, though they are not mandatory. HLA-B27 testing is often performed but is not diagnostic on its own 1.Differential Diagnosis:
Mechanical Low Back Pain: Typically lacks systemic inflammatory markers and responds poorly to NSAIDs.
Rheumatoid Arthritis: Characterized by symmetrical polyarthritis and often positive rheumatoid factor (RF) or anti-cyclic citrullinated peptide (anti-CCP) antibodies.
Psoriatic Arthritis: Often associated with skin or nail psoriasis and dactylitis 1.Management
First-Line Treatment
Nonsteroidal Anti-Inflammatory Drugs (NSAIDs): First-line therapy to reduce pain and inflammation. Commonly used agents include naproxen (750-1000 mg/day) or ibuprofen (800-1600 mg/day). Monitor for gastrointestinal and renal side effects 1.
Physical Therapy: Tailored exercise programs focusing on flexibility, strength, and posture can significantly improve functional capacity and reduce pain 1.Second-Line Treatment
Tumor Necrosis Factor (TNF) Inhibitors: If NSAIDs are ineffective, biologic agents targeting TNF-α, such as adalimumab (40 mg every 2 weeks), etanercept (50 mg twice weekly), or infliximab (5 mg/kg intravenously every 6-8 weeks), are recommended. These should be considered in patients with high disease activity or significant functional impairment 1.
IL-17 or IL-23 Inhibitors: Secukinumab (150 mg or 300 mg monthly) or ustekinumab (initial dose of 90 mg or 160 mg, followed by maintenance dosing) can be effective alternatives or adjuncts in patients who do not respond adequately to TNF inhibitors 1.Refractory Cases / Specialist Escalation
Combination Therapy: Combining biologics targeting different pathways (e.g., TNF inhibitor + IL-17 inhibitor) may be necessary for refractory cases.
Referral to Rheumatology: For complex cases, specialist consultation is crucial to tailor treatment plans, manage comorbidities, and explore advanced therapeutic options 1.Complications
Radiographic Progression: Over time, nr-axSpA can evolve into AS with structural changes visible on X-rays, leading to spinal fusion and functional limitations.
Extra-articular Manifestations: Uveitis, psoriasis, and inflammatory bowel disease can complicate the clinical picture and require multidisciplinary management.
Malignancy: Although rare, there is a slightly increased risk of lymphoma in patients with long-standing inflammatory arthritis, necessitating regular monitoring 1.Prognosis & Follow-up
The prognosis for nr-axSpA varies widely among individuals. Early diagnosis and aggressive management can significantly mitigate disease progression and maintain quality of life. Prognostic indicators include disease activity scores, functional impairment, and response to initial treatment. Recommended follow-up intervals typically include:
Clinical Assessments: Every 3-6 months initially, then annually if stable.
Laboratory Monitoring: CRP and ESR every 6-12 months to assess inflammation.
Imaging: MRI or X-rays every 1-2 years to monitor structural changes 1.Special Populations
Pediatrics: Early onset can present challenges in diagnosis and management, requiring careful monitoring and tailored interventions.
Elderly: Older adults may have atypical presentations and comorbidities that complicate treatment, necessitating individualized care plans.
Comorbidities: Patients with coexisting conditions like cardiovascular disease or diabetes require careful consideration of medication side effects and interactions 1.Key Recommendations
Use ASAS Criteria for Diagnosis: Ensure diagnosis is based on chronic back pain and evidence of inflammation (MRI, elevated CRP/ESR) [Evidence: Strong]
Initiate NSAIDs Early: For pain and inflammation management, with close monitoring for side effects [Evidence: Strong]
Consider TNF Inhibitors for Inadequate Response to NSAIDs: Evaluate response within 12-16 weeks [Evidence: Moderate]
Physical Therapy is Essential: Incorporate regular exercise programs to maintain mobility and reduce pain [Evidence: Moderate]
IL-17 or IL-23 Inhibitors as Second-Line Biologics: For patients unresponsive to TNF inhibitors [Evidence: Moderate]
Regular Follow-Up Monitoring: Include clinical assessments, inflammatory markers, and imaging every 6-12 months [Evidence: Moderate]
Specialist Referral for Complex Cases: Ensure multidisciplinary care for refractory or comorbid conditions [Evidence: Expert opinion]
Screen for Extra-articular Manifestations: Regularly assess for uveitis, psoriasis, and inflammatory bowel disease [Evidence: Moderate]
Monitor for Radiographic Progression: Periodic imaging to track structural changes [Evidence: Moderate]
Tailor Treatment to Individual Needs: Consider age, comorbidities, and response to therapy in treatment planning [Evidence: Expert opinion]References
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