Ankylosing Spondylitiis (courtesy of RadsWiki)

* 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 deformities