Fact-sheet: Ankylosing spondylitis
Updated on 04/18/2017 at 7:19 AM
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Definition
Inflammatory rheumatism of the young adult, with onset between 15 and 30 years of age, preferentially affecting the axial skeleton, the sacroiliac joints, and the large proximal joints.
Male predominance
Laboratory findings
Inflammatory syndrome
Negative rheumatoid factor
HLA B27 antigen (inconstant and not absolutely necessary for diagnosis)
Radiography
Inflammatory enthesopathies are frequent
Sacroiliitis, most often bilateral, not necessarily symmetric, initially predominating on the iliac side
Spinal involvement:
- vertebral squaring
- erosions (C1-C2, spinous processes, superior and inferior vertebral corners, pseudospondylodiskitis)
- enthesophytes progressing to sub-ligamentous ossification and complete ankylosis of the anterior column. Posterior ligamentous ossification, ossification of the ligamentum flavum, ankylosis of the facet joints
- loss of cervical and lumbar lordosis, hyperkyphosis
- fracture
- spinal cord or nerve root compression
Other joints involved: pubic symphysis, hip, shoulder, knee, manubriosternal joints...
MRI
MRI of the sacroiliac joints: indicated early on to confirm the diagnosis. Superior sensitivity to CT for subchondral edema, which appears hypointense on T1 and hyperintense on T2. Involvement is classically bilateral, asymmetric, predominating on the iliac side. At the very onset, it may be unilateral.
Spinal MRI:
- Search for early signs to confirm the diagnosis
- Edema hypointense on T1 and hyperintense on T2 at the anterosuperior and anteroinferior corners of the vertebral bodies, reflecting inflammatory involvement of the peripheral fibers of the annulus fibrosus (Sharpey's fibers) ("shiny corners")
- Spondylitis: edema of a vertebral body
- Costovertebral and costotransverse arthritis
- Rheumatic spondylodiskitis: disk disease associated with erosions and edema of the vertebral endplates adjacent to the intervertebral disk, without discal abscess or extension to the perivertebral soft tissues
Classification
Grade 0 sacroiliitis: normal radiographs
Grade 1 sacroiliitis: questionable radiographs, periarticular osteoporosis
Grade 2 sacroiliitis: subchondral erosions. Blurred or pseudo-widened appearance of the sacroiliac joint space, or "postage stamp" appearance
Grade 3 sacroiliitis: subchondral osteosclerosis and progression of erosions
Grade 4 sacroiliitis: ankylosis
Differential diagnosis
Infectious spondylodiskitis vs. rheumatic spondylodiskitis