From the Guidelines
The diagnostic workup for suspected Ankylosing Spondylitis (AS) should begin with a thorough clinical evaluation, including inflammatory back pain characteristics, followed by laboratory tests such as erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and HLA-B27 testing, and imaging studies, with magnetic resonance imaging (MRI) of the sacroiliac joints being preferred for early detection. The clinical evaluation should focus on characteristics such as morning stiffness lasting more than 30 minutes, improvement with exercise, pain at night with improvement upon arising, and onset before age 45 1. Laboratory tests, including ESR and CRP, may be elevated in active disease, and HLA-B27 testing is recommended as this genetic marker is present in a significant proportion of patients with AS, though it's not diagnostic on its own 1.
Imaging studies are crucial, starting with plain radiographs of the sacroiliac joints and spine to look for sacroiliitis and syndesmophytes. However, early disease may not show radiographic changes, so MRI of the sacroiliac joints is preferred for early detection as it can identify active inflammation before structural damage occurs 1. The Assessment of SpondyloArthritis international Society (ASAS) proposed classification criteria that apply to both patients in the early stage of the disease and those in the later stages, included under the umbrella term axial SpA 1.
Additional assessments should include evaluation for extra-articular manifestations such as uveitis, inflammatory bowel disease, and psoriasis. Referral to a rheumatologist is essential for confirming the diagnosis and initiating appropriate management. This comprehensive approach helps identify AS early, allowing for timely intervention to prevent disease progression and structural damage. The use of tumor necrosis factor inhibitors (TNFi) has greatly altered the approach to the treatment of AS, and recommendations are needed to help optimize care of these patients 1.
Key points to consider in the diagnostic workup include:
- Clinical evaluation focusing on inflammatory back pain characteristics
- Laboratory tests, including ESR, CRP, and HLA-B27 testing
- Imaging studies, with MRI of the sacroiliac joints preferred for early detection
- Evaluation for extra-articular manifestations
- Referral to a rheumatologist for confirmation and management.