Ankylosing Spondylitis Diagnosis and Management
Recognizing Inflammatory Back Pain
- The American College of Radiology recommends that inflammatory back pain be distinguished from mechanical back pain, with key features including insidious onset before age 40-45 years, morning stiffness lasting >30 minutes, pain worsening at night, alternating buttock pain, and improvement with exercise 2, 1
- Inflammatory back pain is present in 70-80% of patients with axial spondyloarthritis, though it also occurs in 5-6% of the general population, requiring further workup to confirm diagnosis 2
Initial Diagnostic Workup
- The American College of Radiology suggests ordering plain radiographs of sacroiliac joints as first-line imaging, with sensitivity of 66% and specificity of 68% for sacroiliitis grade ≥2 bilateral or grade ≥3 unilateral 2, 3
- HLA-B27 testing is recommended, with a positive result in 74-89% of patients, and a post-test probability of 32% when positive in chronic back pain patients 2, 1
- ESR and CRP tests are also recommended, though normal results cannot rule out disease 1, 4
Mandatory Rheumatology Referral Criteria
- The American College of Rheumatology recommends referring patients to rheumatology when they have chronic low back pain (>3 months) starting before age 45, plus at least 4 of the following: back pain occurring before age 35, waking at night due to back pain, buttock pain, improvement in pain with movement or within 2 days of taking an NSAID, first-degree relative with spondyloarthritis, or current or previous arthritis, enthesitis, or psoriasis 4
Initial Management While Awaiting Rheumatology
- The American College of Rheumatology suggests starting NSAIDs at the lowest effective dose, then titrating to maximum tolerated doses, while weighing cardiovascular, gastrointestinal, and renal risks 4
- Approximately 75% of patients show good or very good response within 48 hours of full-dose NSAID therapy 4
Disease Activity Assessment
- The Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) is used to monitor disease activity, evaluating fatigue, spinal pain, peripheral joint pain, and morning stiffness, with a score >4 indicating active disease requiring treatment escalation 3