From the Guidelines
Diagnosing ankylosing spondylitis (AS) requires a systematic approach combining clinical evaluation, laboratory tests, and imaging studies, with the most recent evidence suggesting that MRI of the sacroiliac joints should be performed if conventional X-rays are normal but AS is still suspected, as recommended by the 2021 American College of Radiology (ACR) Appropriateness Criteria 1.
Diagnostic Sequence
The diagnostic process typically begins with a thorough clinical assessment focusing on inflammatory back pain symptoms, including morning stiffness lasting more than 30 minutes, improvement with exercise, and pain that wakes patients at night.
- Next, laboratory tests are ordered, including HLA-B27 genetic testing, C-reactive protein (CRP), and erythrocyte sedimentation rate (ESR) to assess inflammation levels.
- Plain radiographs of the sacroiliac joints and spine are then obtained to look for sacroiliitis and syndesmophytes, though early disease may not show radiographic changes.
- If conventional X-rays are normal but AS is still suspected, magnetic resonance imaging (MRI) of the sacroiliac joints should be performed, as it can detect early inflammatory changes before structural damage occurs, as supported by the Assessment of SpondyloArthritis International Society (ASAS) criteria 1.
Importance of Early Diagnosis
In cases where diagnosis remains unclear, a rheumatology consultation is recommended for expert assessment.
- The diagnosis is ultimately made using the ASAS criteria, which combine imaging findings with clinical features.
- Early diagnosis is crucial as prompt treatment with NSAIDs and potentially biologics like TNF inhibitors can significantly improve outcomes and prevent spinal fusion, as highlighted in the 2019 update of the American College of Rheumatology/Spondylitis Association of America/Spondyloarthritis Research and Treatment Network recommendations for the treatment of ankylosing spondylitis and nonradiographic axial spondyloarthritis 1.
From the Research
Diagnostic Sequence for Ankylosing Spondylitis (AS)
The diagnostic sequence for Ankylosing Spondylitis (AS) involves a combination of clinical evaluation, laboratory tests, and imaging studies. The following steps are involved in the diagnostic sequence:
- Clinical evaluation: A thorough medical history and physical examination are essential to identify symptoms and signs of AS, such as chronic back pain, stiffness, and inflammation in the back, eye inflammation, aortitis, and spinal ankylosis 2.
- Laboratory tests: Inflammatory markers, such as C-reactive protein and erythrocyte sedimentation rate, may be elevated in AS, although they are not specific for the disease 2, 3.
- Imaging studies: Radiographs, such as X-rays, can show sacroiliitis and other spinal changes, but these may not be apparent in early disease 4, 2, 5, 6. Magnetic resonance imaging (MRI) can detect early inflammatory changes and is useful in evaluating disease activity 4, 2, 6.
- HLA-B27 testing: The presence of the HLA-B27 gene can support a diagnosis of AS, although it is not diagnostic on its own 2.
- Diagnostic criteria: Several classification criteria, such as the Ankylosing Spondylitis Assessment Study group (ASAS) criteria, can aid in the diagnosis of AS, but their accuracy is limited 3, 5.
Challenges in Diagnosing AS
Diagnosing AS can be challenging due to the delayed appearance of radiographic sacroiliitis and the lack of specific diagnostic criteria for early disease 5. A comprehensive approach, including a thorough medical history, physical examination, laboratory tests, and imaging studies, is essential to optimize diagnostic accuracy 6.
Diagnostic Algorithm
A diagnostic algorithm based on calculations using Bayes' theorem has been proposed to diagnose axial spondyloarthritis, which includes AS with and without radiographic sacroiliitis 5. This algorithm can help physicians diagnose or exclude axial SpA with a high degree of confidence.
Importance of Early Diagnosis
Early diagnosis of AS is crucial, as it allows for the introduction of effective therapies, such as tumor necrosis factor antagonists, which can suppress disease activity and improve functional ability 2, 6.