![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhRR3n8eKXlBgs2hRDIDnar0ssHdRzMAv7-_y79pHALInDlf0e9I1cQLERDDGtd_MvG3vYXAVChhu9RnTfnYuwKLGi8LC8F5sjUMLVvQw7PcVTq7cZScM0UlIkBOlExvXUOCh5mvqMSkw/s320/seronegative-spondyloarthropathy-as-1.jpg)
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Facts
- SNSA is a group of diseases that general pathology consists of negative rheumatoid factor (RF) and elevated erythrocyte sedimentation rate (ESR)
- Ankylosing spondylitis, reactive spondyloarthropathy, psoriatic spondyloarthropathy, spondyloarthropathy associated with inflammatory bowel disease, undifferentiated spondyloarthropathy
- Strong association with HLA-B27 haplotype
- Most common clinical presentation is low back pain (greater in the morning) and pathologic fracture
Imaging Findings
- First involves sacroiliac joints (erosion of synovial portion, then fusion in late stage), then thoracolumar junction and may involve whole spine
- Corner erosions of vertebral bodies produce "squaring" and reactive sclerosis produces "shiny corner" sign
- "Bamboo spine" caused by thin ossification of the outer fibers of annulus fibrosus at vertebral margin, common in ankylosing spondylitis
Key Differentiating Imaging Features
- Involvement of SI joints - rare in rheumatoid arthritis, normal in DISH, retinoid therapy
- Infection of SI joint typically unilateral
Our case: ankylosing spondylitis
Reference:
Ross, Brant-Zawadzki, Moore, et al. Diagnostic Imaging: Spine, 2004
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