Ankylosing Spondylitis Diagnosis and Management

Clinical Presentation

The American College of Radiology recommends that patients with chronic inflammatory back pain, especially those with onset before age 45, should be evaluated for ankylosing spondylitis, characterized by prolonged morning stiffness (>30 minutes) that improves with exercise but not with rest 1, 2, 3
Patients typically experience nocturnal pain that wakes them up during the second half of the night, and alternating buttock pain indicating sacroiliac joint involvement 1, 2, 3
The American College of Radiology suggests that the presence of inflammatory back pain, improved by exercise and worsened by rest, is a key distinguishing feature from mechanical back pain 1, 2, 3

The American College of Radiology recommends standard radiographs as the first imaging modality, with sacroiliitis grade ≥2 bilateral or grade ≥3 unilateral having a sensitivity of 66% and specificity of 68% for diagnosis 1, 3
MRI can identify early sacroiliitis in symptomatic patients with normal radiographs, and is indicated if radiographs are negative but clinical suspicion remains high 1, 2, 3
The American College of Radiology suggests that MRI findings of bone marrow edema on STIR or T2 sequences with fat saturation indicate active inflammation, with a sensitivity of 78% and specificity of 88% 1

The Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) is a validated clinical index that evaluates fatigue, spinal pain, peripheral joint pain, and morning stiffness, with a score >4 indicating active disease 4, 5, 6
The Annals of the Rheumatic Diseases recommend using the BASDAI, along with other indices such as the Bath Ankylosing Spondylitis Functional Index (BASFI) and the Bath Ankylosing Spondylitis Metrology Index (BASMI), to assess disease activity and functional capacity 4, 5

The American College of Radiology warns against confusing inflammatory back pain with mechanical back pain, as the former improves with movement, while the latter worsens 2
The Journal of the American College of Radiology advises against waiting for radiographic changes, as MRI can provide an early diagnosis before structural changes appear 1, 3
The Annals of the Rheumatic Diseases recommend not relying solely on inflammatory markers, as they can be normal despite active disease 1