From the Guidelines
The diagnostic criteria for ankylosing spondylitis include a combination of clinical features, imaging findings, and laboratory tests, with the Assessment of SpondyloArthritis International Society (ASAS) criteria being commonly used, as outlined in the 2021 update of the ACR Appropriateness Criteria for inflammatory back pain 1. The ASAS criteria require sacroiliitis on imaging (X-ray or MRI) plus at least one spondyloarthritis feature, or HLA-B27 positivity plus at least two spondyloarthritis features. These features include:
- Inflammatory back pain lasting more than three months with onset before age 45
- Limited spinal mobility
- Peripheral arthritis
- Enthesitis (especially at the heel)
- Uveitis
- Dactylitis
- Psoriasis
- Inflammatory bowel disease
- Good response to NSAIDs
- Family history of spondyloarthritis
- Elevated C-reactive protein Radiographic evidence of sacroiliitis on plain X-rays has traditionally been important, but MRI can detect earlier inflammatory changes before structural damage occurs, as noted in the 2017 ACR Appropriateness Criteria for chronic back pain suspected sacroiliitis-spondyloarthropathy 1. HLA-B27 genetic testing is supportive but not diagnostic on its own, as it's present in 90% of patients with ankylosing spondylitis but also in 8% of the general population. Early diagnosis is crucial as it allows for prompt treatment with NSAIDs, physical therapy, and potentially biologic medications like TNF inhibitors or IL-17 inhibitors to prevent spinal fusion and disability, as recommended in the 2016 American College of Rheumatology/Spondylitis Association of America/Spondyloarthritis Research and Treatment Network guidelines for the treatment of ankylosing spondylitis and nonradiographic axial spondyloarthritis 1.
The most recent and highest quality study, the 2021 ACR Appropriateness Criteria for inflammatory back pain 1, provides the most up-to-date guidance on the diagnosis of ankylosing spondylitis, emphasizing the importance of a combination of clinical features, imaging findings, and laboratory tests in making an accurate diagnosis. The use of MRI in the diagnostic algorithm, as outlined in the ASAS criteria, allows for the detection of earlier inflammatory changes and the diagnosis of patients with nonradiographic axial spondyloarthritis, who may not have radiographic evidence of sacroiliitis. Overall, the diagnosis of ankylosing spondylitis requires a comprehensive approach, taking into account clinical features, imaging findings, and laboratory tests, with the goal of early diagnosis and prompt treatment to prevent long-term disability and improve quality of life.
From the Research
Diagnostic Criteria for Ankylosing Spondylitis
The diagnostic criteria for ankylosing spondylitis (AS) involve a combination of clinical symptoms, signs, and radiological findings. Some key points to consider include:
- Chronic back pain and stiffness are common symptoms of AS, and early diagnosis requires a high index of suspicion and clinical experience 2.
- Inflammatory markers such as C-reactive protein and erythrocyte sedimentation rate may be elevated, but are not always present 3.
- Radiographic changes, such as sacroiliitis and spinal ankylosis, are important for diagnosis, but may not be present in early disease 4.
- Magnetic resonance imaging (MRI) can be useful in evaluating early disease and detecting inflammatory changes in the sacroiliac joints and spine 5.
- The presence of the HLA-B27 gene can support the diagnosis, as it is present in 80-95% of people with AS 4.
Clinical Signs and Symptoms
Clinical signs and symptoms of AS include:
- Stiffness and inflammation in the back
- Eye inflammation
- Aortitis (inflammation of the aorta)
- Spinal ankylosis that impacts posture and fatigue
- The dagger sign and sacroiliitis on radiographs are crucial for diagnosis 4.
Diagnostic Tools
Diagnostic tools for AS include:
- MRI to detect early inflammatory changes in the sacroiliac joints and spine 5
- Radiographs to detect sacroiliitis and spinal ankylosis 4
- Laboratory tests, such as C-reactive protein and erythrocyte sedimentation rate, to support the diagnosis 3
- HLA-B27 gene testing to support the diagnosis 4.
Challenges in Diagnosis
Diagnosing AS can be challenging due to the lack of a diagnostic gold standard and the similarity of its symptoms to those of other conditions 5. A comprehensive approach, including a complete history, laboratory testing, and imaging, is crucial to optimize diagnostic accuracy 5.