Discussion of Ankylosing spondylitis
- an autoimmune spondyloarthropathy
- a.k.a. Bechterew's disease/syndrome and Marie Strümpell disease
- chronic, progressive inflammatory arthritis
- primarily affects the spine and sacroiliac joints, causing eventual fusion
- may result in complete spinal rigidity - known as bamboo spine
- diffuse paraspinal ossification and inflammatory osteitis creates a fused, brittle spine, susceptible to fracture.
- even minor trauma may produce fracture in these patients!
- fractures more common in thoracolumbar and cercivothoracic junctions in patients with ankylosing spondylitis.
- pulmonary sequellae, with progressive fibrosis and apical bullae formation are seen several years after joint involvement
- Treatment includes inflammatory modulators such as the TNF-alpha receptor fusion protein etanercept and the IL-1 receptor antagonis anakinra
 Imaging Findings for Ankylosing spondylitis
- indistinct joints
- joints widen before narrow
- subchondral erosions, sclerosis, and proliferation on iliac side of SI joints
- at endstage, sacroiliac joint may be a thin line or not visible
- in the spine, early spondylitis is characterized by small erosions at the corners of vertebral bodies with reactive sclerosis
- squaring of the vertebral body
- syndesmophyte formation, with bridging of the corners of one vertebra to another
- ossification of paravertebral connective tissue fibers, including posterior interspinous ligaments as well as linking of spinous processes leads to an appearance of a solid midline vertical dense line on AP projection
- may see associated pseudoarthroses (discovertebral destruction with adjacent sclerosis) and enthesopathic changes (ill-defined erosions with adjacent sclerosis at sites of ligamentous and tendenous attachments)
- hip involvement is generally bilateral and symmetric, with uniform joint space narrowing, axial migration of the femoral head, and a collar of osteophytes at the femoral head-neck junction
- knees demonstrate uniform joint space narrowing with bony proliferation
- hands are generally involved asymmetrically, with smaller, shallower erosions and marginal periostitis.
- radiographs of the lungs may demonstrate progressive fibrosis and bullous changes at the apices. These lesions may resemble TB infection and bullae may become infected.
- may be useful in selected patients with normal or equivocal findings on sacroiliac joint radiographs
- joint erosions, subchondral sclerosis, and bony ankylosis are better visualized on CT
- some normal variants of the SI joints may mimic features of sacroiliitis
- CT supplements scintigraphy in evaluated areas of increased uptake
- multidetector CT is superior to radiographs and MRI in demonstrating injuries
- MDCT is imaging modality of choice in patients with advanced ankylosing spondylitis for whom there is suspicion of cervical spine fracture
- May have a role in early diagnosis of sacroiliitis
- Synovial enhancement on MR correlates with disease activity measured by inflammatory mediators
- Superior to CT in detection of cartilage, bone erosions, and subchondral bone changes
- Increased T2 signal correlates with edema or vascularized fibrous tissue
- Useful in following treatment results in patients with active ankylosing spondylitis
 Bone scintigraphy
- May be helpful in selected patients with normal or equivocal findings on sacroiliac joint radiographs
- Qualitative assessment of accumulation of radionuclides in the SI joints may be difficult due to normal uptake in this location. Thus quantitative analysis may be more useful.
- Ratios of SI joint to sacral uptake of 1.3:1 or higher is abnormal
- recognition of minimally displaced fractures is difficult due to osteopenia and deformity
- important to specifically search for disk space widening and discontinuity of the ossified paraspinal ligaments
- with CT, sagittal reformats should be obtained as axial images poorly assess the transverse fracture plane
- MR and radionuclide scintigraphy may be helpful in difficult cases
Patient #1: AS with dural ectasia
Patient #2: Bamboo Spine
Patient #3: Symmetrical sacroiliac joint fusion
 See Also
- Upper lobe predominance mnemonic
- Inflammatory bowel disease arthritis
- Psoriatic arthritis
- Reiter's syndrome
 External Links
 References for Ankylosing spondylitis
- Baraliakos, X, Landewé, R, Hermann, KG, et al. Inflammation in ankylosing spondylitis: a systematic description of the extent and frequency of acute spinal changes using magnetic resonance imaging. Ann Rheum Dis 2005 May; 64(5): 730-4.
- Bennett, D.L., Ohashi, K., El-Khoury, G.Y. Spondyloarthropathies: ankylosing spondylitis and psoriatic arthritis. Radiol Clin North Am 2004 Jan; 42(1): 121-34.
- Cawley, M.I., Chalmers, T.M., Kellgren, J.H., Ball, J. Destructive lesions of vertebral bodies in ankylosing spondylitis. Ann Rheum Dis 1972 Sep; 31(5): 345-58.
- Dihlmann, W. Current radiodiagnostic concept of ankylosing spondylitis. Skeletal Radiol 1979; 4(4): 179-88.
- Fam, A.G., Rubenstein, J.D., Chin-Sang, H., Leung, F.Y. Computed tomography in the diagnosis of early ankylosing spondylitis. Arthritis Rheum 1985 Aug; 28(8): 930-7.
- Graham, B., Van Peteghem, P.K. Fractures of the spine in ankylosing spondylitis. Diagnosis, treatment, and complications. Spine 1989 Aug; 14(8): 803-7.
- Hanson, J.A., and Mirza, S. Predisposition for spinal fracture in ankylosing spondylitis. AJR 2000; 174:150.
- Karasick, D., Schweitzer, M.E., Abidi, N.A., Cotler, J.M. Fractures of the vertebrae with spinal cord injuries in patients with ankylosing spondylitis: imaging findings. AJR Am J Roentgenol 1995 Nov; 165(5): 1205-8.