Ankylosing spondylitis
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Ankylosing spondylitis (less commonly known as Bechterew disease and Marie Strümpell disease) is a seronegative spondyloarthropathy, which as the name suggests, results in fusion (ankylosis) of the spine and sacroiliac (SI) joints, although involvement is also seen in large and small joints.
Epidemiology
There is male predilection of 3:1 or more. It usually manifests in adults, with the first symptoms becoming evident in the third decade, although up to 18% of cases manifest in the second decade.
Pathology
Genetics
Patients are rheumatoid factor (RF) negative (hence seronegative). Approximately 90% of Caucasian individuals have the HLA-B27 gene 5.
Associations
- anterior uveitis
- psoriasis
- ulcerative colitis/Crohn disease
- upper lobe predominant interstitial lung disease with small cystic spaces (occurs in ~1% of patients) 4
- aortic valve disease/aortitis
- amyloidosis (rare)
Radiographic features
Features predominantly affect the axial skeleton although can involve the peripheral joints in ≈20% of cases.
Plain radiograph
Sacroiliac joints
- sacroiliitis is usually the first manifestation 5 and is symmetrical and bilateral
- joints widen before they narrow
- subchondral erosions, sclerosis and proliferation on the iliac side of SI joints
- at endstage, the SI joint may be a thin line or not visible
See: grading of sacroiliitis.
Spine
- early spondylitis is characterised by small erosions at the corners of vertebral bodies with reactive sclerosis (Romanus lesions of the spine: shiny corner sign)
- vertebral body squaring
- diffuse syndesmophyitic ankylosis can give a "bamboo spine" appearance
- interspinous ligament calcification can give a "dagger spine" appearance
- ossification of spinal ligaments, joints and discs (with fatty marrow within ossified disc, best seen on MRI)
- apophyseal and costovertebral arthritis and ankylosis
- pseudoarthroses may form at fracture sites
- enthesophyte formation from enthesopathy
- non-infectious spondylodiscitis: Andersson lesion
Hips
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
Knees demonstrate uniform joint space narrowing with bony proliferation.
Hands
Hands are generally involved asymmetrically, with smaller, shallower erosions and marginal periostitis.
Shoulders
Shoulder joint involvement is not uncommon and demonstrate large erosion of anterolateral aspect of humeral head producing 'hatchet' deformity.
Chest
Radiographs of the lungs may demonstrate progressive fibrosis and bullous changes at the apices. These lesions may resemble tuberculosis infection and bullae may become infected.
CT
- may be useful in selected patients with normal or equivocal findings on sacroiliac joint radiographs
- joint erosions, subchondral sclerosis, and bony ankylosis are better visualised on CT
- some normal variants of the SI joints may mimic features of sacroiliitis
- supplements scintigraphy in evaluating areas of increased uptake
- superior to radiographs and MRI in demonstrating injuries
- imaging modality of choice in patients with advanced ankylosing spondylitis for whom there is suspicion of cervical spine fracture
- sagittal reformats should be obtained as axial images poorly assess the transverse fracture plane
MRI
- may have a role in early diagnosis of sacroiliitis
- synovial enhancement on MR correlates with disease activity measured by inflammatory mediators
- enhancement of the interspinuous ligamants is indicative of an enthesitis
- increased T2 signal correlates with edema or vascularised fibrous tissue
- superior to CT in detection of cartilage, bone erosions, and subchondral bone changes
- 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
Treatment and prognosis
Treatment includes NSAIDs, physiotherapy and, for more severe cases, anti-TNF-alpha therapy.
Complications
- fracture
- diffuse paraspinal ossification and inflammatory osteitis creates a fused, brittle spine, susceptible to fracture, even with minor trauma
- more common at the thoracolumbar and cervicothoracic junctions
- recognition of minimally displaced fractures is difficult due to osteopenia and deformity, and it is important to specifically search for disk space widening and discontinuity of the ossified paraspinal ligaments
- also known as "carrot stick fractures" 15
- Andersson lesion: inflammatory spondylodiscitis that occurs in association with ankylosing spondylitis and results in a disc pseudarthrosis
- rare neurological complications include transverse myelitis and/or cauda equina syndrome 16, 17
Differential diagnosis
- general spine: enteropathic arthritis
- cervical spine: juvenile rheumatoid arthritis (JRA)
- diffuse idiopathic skeletal hyperostosis
See also
- +<li>apophyseal and costovertebral arthritis and ankylosis</li>
Image 32 MRI (T1) ( create )
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