Sacroiliitis Diagnosis and Characteristics

Clinical Signs

The American College of Rheumatology suggests that inflammatory back pain characteristics include insidious onset before age 45 years with chronic duration (≥3 months) 1
Prolonged morning stiffness lasting more than 30 minutes is a key feature of sacroiliitis 2
Improvement with exercise but not with rest is a critical distinguishing feature of inflammatory back pain 2
Night pain, particularly awakening in the second half of the night, is a common symptom of sacroiliitis 1
Alternating buttock pain indicating sacroiliac joint involvement is a characteristic of sacroiliitis 3
Direct palpation tenderness over the sacroiliac joints is a key examination finding 3

The European League Against Rheumatism recommends that sacroiliitis grade ≥2 bilaterally or grade ≥3 unilaterally on x-ray examination is diagnostic of sacroiliitis (sensitivity 66%, specificity 68%) 4
Radiological evidence of sacroiliitis occurs in 20-50% of patients with inflammatory bowel disease-associated spondyloarthritis 5, 6
Active inflammation on fluid-sensitive sequences (STIR or fat-saturated T2-weighted) showing bone marrow edema is a characteristic of sacroiliitis (sensitivity 78%, specificity 88%) 5, 6
MRI can identify early sacroiliitis in symptomatic patients with normal plain radiography (non-radiographic spondyloarthritis) 5, 6

Elevated ESR is found in patients with ankylosing spondylitis, but sensitivity is only 50% 8
HLA-B27 positivity is found in 74-89% of patients with axial spondyloarthritis, but has lower prevalence in IBD-associated sacroiliitis 1, 5, 6

The Assessment of SpondyloArthritis international Society (ASAS) recommends that for patients with chronic back pain >3 months with first symptoms <45 years, assess for inflammatory back pain features (sensitivity 74-81%, specificity 25-44%) 8
If inflammatory back pain present or HLA-B27 positive, proceed to imaging, starting with plain radiographs of sacroiliac joints 8, 4
If radiographs normal but clinical suspicion high, obtain MRI of sacroiliac joints 5, 6
Refer to rheumatologist for further evaluation when sacroiliitis confirmed by imaging 8