eMedicine Specialties > Radiology > Musculoskeletal

Ankylosing Spondylitis

Wilfred CG Peh, MD, MBBS, FRCP(Glasg), FRCP(Edin), FRCR, Clinical Professor, Faculty of Medicine, National University of Singapore; Senior Consultant Radiologist, Alexandra Hospital, Singapore

Updated: Mar 25, 2009

Introduction

Background

Ankylosing spondylitis is a distinct disease entity characterized by inflammation of multiple articular and para-articular structures, frequently resulting in bony ankylosis. The term ankylosing is derived from the Greek word ankylos, meaning stiffening of a joint; the term spondylos means vertebra. Spondylitis refers to inflammation of one or more vertebrae. Ankylosing spondylitis usually is classified as a chronic and progressive form of seronegative arthritis.

Bilateral chronic sacroiliitis. Frontal radiograph shows complete fusion of both sacroiliac joints.

Romanus lesions. Lateral radiograph shows anterior corner erosions at the T12 and L1 vertebral bodies. The typical shiny corner sign (or Romanus lesion) is present (arrows).

Pathophysiology

Enthesopathy

The basic pathologic lesion of ankylosing spondylitis occurs at the entheses, which are sites of attachment to bone of ligaments, tendons, and joint capsules. Enthesopathy results from inflammation, with subsequent calcification and ossification at and around the entheses. Inflammation with cellular infiltration by lymphocytes, plasma cells, and polymorphonuclear leukocytes is associated with erosion and eburnation of the subligamentous bone. The process usually starts at the sacroiliac joints. Other enthesopathic sites include the iliac crest, ischial tuberosity, greater trochanter, patella, and calcaneum. In the paravertebral soft tissues, the lesion manifests as a formation of new bone within the outer layers of the annulus fibrosis of the intervertebral disk. The margins of the disk are invaded by hyperemic granulation tissue arising from the subchondral bone. This tissue replaces the disk fibers with new bone.

Synovial joints

In the synovial joints, a proliferative chronic synovitis indistinguishable from rheumatoid arthritis may occur; however, subchondral bone and cartilage are invaded by reactive tissue originating from the bone, which is a feature not encountered in rheumatoid arthritis. Capsular fibrosis and bony ankylosis tend to occur. Formation of bony bridges between adjacent vertebrae (syndesmophytes) and progressive ossification of extraspinal joint capsules and ligaments are characteristic of the disease. Unlike rheumatoid arthritis, pannus formation is not known to occur.

Genetics

The etiology of ankylosing spondylitis is unknown; however, a strong genetic influence exists. A family history of the disease is common in patients with ankylosing spondylitis. Approximately 90-95% of patients with ankylosing spondylitis have the tissue antigen human leukocyte antigen B27 (HLA-B27); by comparison, HLA-B27 is present in 7% of the general population. Because only 1% of individuals who have HLA-B27 develop ankylosing spondylitis, the disease is likely triggered by an unknown environmental factor in persons who are genetically predisposed.

Frequency

United States

It is estimated that ankylosing spondylitis affects approximately 0.1-0.2% of the general population.

International

Internationally, ankylosing spondylitis occurs with a frequency identical with that in the United States.

Mortality/Morbidity

The life expectancy of patients with ankylosing spondylitis is the same as that of the general population, except for patients who are severely affected with the disease and in whom complications develop. The morbidity of ankylosing spondylitis may be considerable; it is estimated that fewer than 20% of patients with adult-onset disease develop significant morbidity. Most patients are able to maintain a normal lifestyle, and patients should be encouraged and counseled to do so. In fact, many mild cases may go undetected.

Race

The prevalence of ankylosing spondylitis is lower in blacks and in certain North American Indian tribes.

Sex

Ankylosing spondylitis primarily affects young males. The male-to-female ratio is 4-10:1. The true prevalence in females may be higher than reported, and the disease may be more subtle and difficult to diagnose in female patients. Ankylosing spondylitis tends to follow a more mild and benign course in females.

Age

Ankylosing spondylitis typically affects young males. The peak age of onset is 15-35 years; the mean age of onset is 26 years. In approximately 15-20% of patients, the disease begins in the second decade of life. In 10%, onset occurs after 39 years of age. Hip and peripheral joint involvement is more frequent and severe in juveniles than in adults.

Anatomy

The classic initial site of involvement of ankylosing spondylitis is the sacroiliac joint, followed by the thoracolumbar and lumbosacral junctions. As the disease progresses, the mid lumbar, upper thoracic, and cervical vertebrae are affected. Although considered characteristic, the disease does not always ascend up the spine. In general, atypical patterns occur more frequently in women; spinal disease without sacroiliac joint involvement is unusual in either sex.

Peripheral joint involvement tends to occur more frequently in cases of chronic ankylosing spondylitis. Radiographic changes are seen in more than 50% of patients with long-standing ankylosing spondylitis. The hip joint is affected most often; the glenohumeral and knee joints are involved in approximately 30% of patients. With time, diffuse articular disease occurs, with involvement of the hands, wrists, and feet.

Radiographic changes are seen at the pubic symphysis, often in combination with sacroiliitis. Other involved cartilaginous sites in the axial skeleton include the manubriosternal, acromioclavicular, and sternoclavicular joints. Enthesopathic changes are frequently seen at sites of tendinous and ligamentous attachments such as the ischial tuberosity, iliac crest, trochanters of the femur, and the inferior calcaneum.

Presentation

History

The most common presenting symptom of patients with ankylosing spondylitis is low back pain. Usually, pain is centered over the sacrum; it may radiate to the groin and buttocks and down the legs. The typical patient is a young man who has repeated episodes of being wakened at night with back pain; the back pain is associated with spinal stiffness in the morning. Low back pain persists, even at rest. The pain pattern is characteristic of bilateral sacroiliitis.

With time, back pain progresses up the spine and affects the rib cage. Chest expansion becomes restricted as the costovertebral joints become involved. The patient must practice diaphragmatic breathing, which may be observed as ballooning of the abdomen during inspiration. The cervical spine is ankylosed late in the course of the disease, leading to restriction in neck movement and head rotation. Eventually, the spine is completely rigid, with loss of the normal curvatures and movement.

Physical examination

Loss of lateral flexion of the lumbar spine is the earliest objective sign of spinal involvement. Sacroiliitis may be detected by encountering a tenderness response during percussion over the sacroiliac joints and encountering a pain response by springing the pelvis. Several tests have been designed to measure spinal restriction that occurs with disease progression; these include touching the toes, applying the Schober test, and measuring chest expansion. Synovitis and restriction of joint motion may be encountered during examination of the peripheral joints. Tenderness over the entheses, especially the heel, should be sought.

Patients should be examined for the development of complications. Cardiovascular complications include aortic incompetence secondary to aortitis; rarer cardiovascular complications include conduction defects, cardiomyopathy, and pericarditis. In a minority of patients, a restrictive ventilatory pattern develops as a result of limited chest expansion.

Chest complications include apical fibrosis and cavitation. Anterior uveitis is the most common extra-articular manifestation of the disease; it affects approximately 20% of patients. Eye symptoms usually precede spinal symptoms; there is a temporal association between eye symptoms and peripheral arthritis.

Neurologic complications are rare and include radiculitis caused by nerves running over inflamed sacroiliac joints in early disease and spinal cord damage from traumatic fractures of the ankylosed spine in late disease. Amyloidosis is a rare complication of long-standing disease and may lead to renal failure.

Laboratory investigations

The erythrocyte sedimentation rate is elevated during the acute phase of the disease. Mild leukocytosis may occur. In chronic disease, a normochromic normocytic anemia may develop. Gamma-globulin levels may be raised. Rheumatoid factors are negative. Human leukocyte antigen typing shows the presence of B27 in as many as 95% of patients, although this test cannot be used diagnostically because only a small percentage of individuals with positive test results for HLA-B27 develop the disease.⁴

Treatment

Once a definitive diagnosis is established, a detailed explanation of the disease, including its implications, should be provided to the patient. Regular lifelong exercises are the mainstay of the treatment program. Adequate analgesics in the form of nonsteroidal anti-inflammatory drugs should be administered under supervision to control pain and stiffness and to allow the patient to continue exercising through pain. Severe hip involvement may require hip replacement surgery. Spinal surgery may be required to treat complications of long-standing spinal disease. For example, in the cauda equina syndrome in ankylosing spondylitis (CES-AS syndrome), surgery either by lumboperitoneal shunting or laminectomy may be required to improve neurologic dysfunction.

Diagnostic criteria

Specific criteria for the diagnosis of ankylosing spondylitis were developed at rheumatic disease conferences in Rome and New York; these criteria have come to be referred to as the Rome criteria (1963) and the New York criteria (1968), respectively. Although the criteria generally have been accepted as useful, limitations have been recognized, and overlaps exist among clinical and radiologic features of various seronegative spondyloarthropathies. The British Society for Rheumatology recommends that the so-called modified New York criteria be used to diagnose ankylosing spondylitis. Sacroiliitis is the hallmark of ankylosing spondylitis and is a requisite for the diagnosis under these sets of criteria.

• Rome criteria (1963): Ankylosing spondylitis is present if bilateral sacroiliitis is associated with any single criterion.
  • Low back pain and stiffness of more than 3 months' duration
  • Pain and stiffness in the thoracic region
  • Limited motion in the lumbar region
  • Limited chest expansion
  • History of evidence of iritis or its sequelae
• New York criteria (1968): Definite ankylosing spondylitis is present if grade 3-4 bilateral sacroiliitis is associated with at least one clinical criterion or if grade 3-4 unilateral or grade 2 bilateral sacroiliitis is associated with clinical criterion 1 or with both clinical criteria 2 and 3. Probable ankylosing spondylitis is present if grade 3-4 bilateral sacroiliitis is associated with none of the criteria.
  1. Limitation of motion of the lumbar spine in anterior flexion, lateral flexion, and extension
  2. History of pain or the presence of pain at the thoracolumbar junction or in the lumbar spine
  3. Limitation of chest expansion to 1 inch or less

• Modified New York Criteria (1984): Definite ankylosing spondylitis is present if the radiologic criterion is present in addition to at least one clinical criterion. Probable ankylosing spondylitis is present if three clinical criterion are present alone or if the radiologic criterion is present but no clinical criteria are present.
  • Clinical criteria
    • 1. Low back pain: present for more than 3 months, improved by exercise but not relieved by rest.
    • 2. Limitation of lumbar spine motion in sagittal and frontal planes.
    • 3. Limitation of chest expansion relative to normal values for age and sex.
  • Radiologic criterion
    • Sacroiliitis on radiographs

Classification of functioning and health

The Assessment of SpondyloArthritis International Society (ASAS) has created 2 Core Sets (comprehensive and brief) for the classification of functioning and health in patients who have ankylosing spondylitis. The Comprehensive International Classification of Functioning and Health (ICF) Core Set includes 80 categories consisting of body functions, body structures, activities and participation, and environmental factors. The Brief ICF Core Set has 19 categories.⁵

Preferred Examination

Radiographs are the single most important imaging technique for the detection, diagnosis, and follow-up monitoring of patients with ankylosing spondylitis. Overall bony morphology and subtle calcifications and ossifications may be demonstrated well radiographically. The diagnosis may be reliably made if the typical radiographic features of ankylosing spondylitis are present.

CT is useful in selected situations (eg, in equivocal cases of sacroiliitis and in cases in which subtle radiographic changes are present) and in the evaluation of complications.

MRI is useful in assessing early cartilage abnormalities and bone marrow edema.^6,7,8,9

Limitations of Techniques

Radiographs are limited in detecting early sacroiliitis and in demonstrating subtle changes in the posterior elements of the vertebrae.

CT is useful in evaluating sacroiliitis, but normal variations of the sacroiliac joints may simulate the findings of inflammation. CT is not ideal for imaging long segments of the spine because of its high radiation dose.

MRI is limited by its relatively poor ability to detect calcification, ossification, and cortical bony changes.

Scintigraphy has been used to detect early sacroiliitis, but there are conflicting reports as to its accuracy.

Differential Diagnoses

[Reiter Syndrome, Musculoskeletal]
Diffuse Idiopathic Skeletal Hyperostosis
Gout
Psoriatic Arthritis
Rheumatoid Arthritis, Spine
Spondylodiskitis

Other Problems to Be Considered

Enteropathic arthropathies
Osteitis condensans ilii

Radiography

Findings

• Sacroiliitis occurs early in the course of ankylosing spondylitis and is regarded as a hallmark of the disease.
• Radiographically, the earliest sign is indistinctness of the joint. The joints initially widen before they narrow.
• Subchondral bony erosions on the iliac side of the joint are seen (see Image 1); these are followed by subchondral sclerosis and bony proliferation.

Bilateral sacroiliitis. Frontal radiograph shows bilateral sacroiliac joint erosions and iliac side subchondral sclerosis.

Bilateral chronic sacroiliitis. Frontal radiograph shows complete fusion of both sacroiliac joints.

• With eventual bony fusion, the sclerosis resolves (see Image 2).
• At the end stage, the sacroiliac joint may be seen as a thin dense line, or it may not be visible at all.
• Sacroiliitis typically is symmetric, although it may be asymmetric in the early stages of the disease.
• In the spine, the early stages of spondylitis are manifested as small erosions at the corners of the vertebral bodies. The areas are surrounded by reactive sclerosis and have been termed the shiny corner sign or Romanus lesion (see Image 3).

Romanus lesions. Lateral radiograph shows anterior corner erosions at the T12 and L1 vertebral bodies. The typical shiny corner sign (or Romanus lesion) is present (arrows).

Vertebral body squaring. Lateral radiograph shows squaring of L3 and L4 vertebral bodies, L3-L4 anterior syndesmophyte, and lumbar facet joint fusion.

• Squaring of the vertebral body is another characteristic feature of ankylosing spondylitis; it is caused by a combination of corner erosions and periosteal new bone formation along the anterior aspect of the vertebral body. This is best seen in the lumbar spine, in which the anterior cortex of the vertebral body normally is concave.
• This is followed by syndesmophyte formation; this term refers to the process in which ossification of the outer fibers of the annulus fibrosis leads to bridging of the corners of one vertebra to another (see Image 4).
• Ossification of the adjacent paravertebral connective tissue fibers also occurs. Posterior interspinous ligament ossification, combined with linking of the spinous process, produces an appearance of a solid midline vertical dense line on frontal radiographs (see Image 5).

Interspinous ossification. Frontal radiograph shows T12-L2 lateral syndesmophytes and interspinous ligament ossification extending from the T12 to L1 and L2 to L4 levels.

Vertebral fusion. Lateral radiograph shows solid ankylosis of all cervical facet joints from C2 downwards. Extensive anterior and posterior syndesmophytes is noted.

• The apophyseal and costovertebral joints frequently are affected by erosions and eventually undergo fusion (see Image 6).
• Complete fusion of the vertebral bodies by syndesmophytes and other related ossified areas produces bamboo spine (see Image 7).
• Calcifications of the disk may occur at single or multiple levels; they are usually associated with apophyseal joint ankylosis and adjacent syndesmophytes (see Image 8).

Bamboo spine. Frontal radiograph shows complete fusion of the vertebral bodies. Extensive facet joint ankylosis and posterior ligamentous ossification produce the trolley track appearance.

Disk calcification. Lateral radiograph shows L2-L3 and L3-L4 disk calcifications, as well as L2-L4 anterior syndesmophytes.

• For patients with established ankylosing spondylitis, fractures usually occur at the thoracolumbar (see Image 9) and cervicothoracic junctions. Upper cervical spine fractures and atlantoaxial subluxation rarely are seen. Fractures typically are transverse, extend from anterior to posterior, and frequently pass through the ossified disk. They have been termed chalk stick fractures (see Image 10).
• Pseudoarthrosis is seen radiographically as areas of diskovertebral destruction and adjacent sclerosis. The changes, which are referred to as the Andersson lesion, may resemble disk infection, although pseudoarthrosis usually develops secondarily to a previously undetected fracture or at an unfused segment. Therefore, an important imaging feature is the involvement of the posterior elements, seen as a linear hypodense area with sclerotic borders (see Image 11).

Thoracolumbar junction fracture. Lateral radiograph shows features of established ankylosing spondylitis. A T12 vertebral body fracture is noted, with disruption of the ossified anterior longitudinal ligament (arrow). An old L1 compression fracture is present.

Chalk stick fracture. Lateral radiograph shows a fracture through the ankylosed cervical spine, producing a gap at the C6-C7 disk.

• Enthesopathy is seen radiographically as ill-defined erosions with adjacent sclerosis at the sites of ligamentous and tendinous attachments. With healing, sclerosis decreases and new bone proliferation occurs. Lesions typically are bilateral and symmetric in distribution. Enthesopathic changes are particularly prominent at certain sites around the pelvis, such as the ischial tuberosity (see Image 12), iliac crest, and femoral trochanters. Other locations include the coracoclavicular ligament attachment site to the inferior clavicle (see Image 13), humeral tuberosity, anterior patella, and plantar aspect of the calcaneum.
• Hip joint involvement typically is bilateral and symmetric. The hip joint space is narrowed uniformly. Axial migration of the femoral head occurs, and a collar of osteophytes may be seen at the femoral head-neck junction (see Image 14).

Pseudoarthrosis. Lateral radiograph shows a T11-T12 diskovertebral lesion with adjacent sclerosis (Andersson lesion; arrow). Posterior element defect is present (arrowheads). The patient also has a severe kyphotic deformity.

Pelvic enthesopathy. Frontal radiograph shows ill-defined erosions with adjacent sclerosis at the left ischial tuberosity and more established new bone formation on the right side.

• Protrusio acetabuli develops in as many as one third of patients.
• Bony ankylosis eventually may occur.
• At the glenohumeral joint, the joint space narrows uniformly, and a large erosion may be present in the upper greater tuberosity.
• Knee changes consist of uniform joint space narrowing and surrounding bony proliferation.
• In the hands, the joints usually are involved asymmetrically. Erosions are smaller and shallower. Marginal periostitis is seen, and bony density usually is preserved.

Shoulder enthesopathy. Frontal radiograph shows irregular bony proliferation at the coracoclavicular ligament attachment sites to the inferior clavicle and the superior coracoid process.

Hip joint changes. Frontal radiograph shows uniform joint space narrowing and a collar of osteophytes at the femoral head-neck junction. Left sacroiliac joint ankylosis is present.

• Lung manifestations of ankylosing spondylitis are seen as progressive fibrosis and bullous changes at the apices. On radiographs, chest lesions may resemble tuberculous infection. Lung bullae may be complicated by infection by Aspergillus species and other opportunistic infections. Lung changes usually are seen several years after joint disease develops.

Degree of Confidence

Radiographs are a reliable means with which to make a diagnosis, particularly if typical radiographic features are present.

False Positives/Negatives

The sacroiliitis associated with ankylosing spondylitis should be differentiated from sacroiliitis caused by other diseases. Bilateral symmetric sacroiliac joint disease may be found in conditions such as psoriasis, Reiter disease, enteropathic arthropathy, hyperparathyroidism, and osteitis condensans ilii.

Ankylosing spondylitis also may present as a bilateral asymmetric sacroiliitis, mimicking psoriasis, Reiter disease, rheumatoid arthritis, and gouty arthritis. Unilateral distribution of sacroiliac disease also may be found in infective arthritis; therefore, it is important that radiographic features be carefully analyzed to look for signs of various diseases and that radiographic features be correlated with the overall pattern of bony involvement and the clinical findings.

Spinal abnormalities found in ankylosing spondylitis may be encountered in other diseases, such as enteropathic arthropathy, psoriasis, and Reiter disease. Careful analysis and classification of bony outgrowths in the vertebrae are helpful in differentiating the various conditions. In addition to ankylosing spondylitis, syndesmophytes are found in alkaptonuria. Flowing anterior ossification is a feature of diffuse idiopathic skeletal hyperostosis, whereas paravertebral ossification is present in both psoriasis and Reiter disease.

Spinal pseudoarthrosis in ankylosing spondylitis often produces marked diskovertebral destructive changes that may resemble infective spondylodiskitis. The presence of posterior element fracture or defect is an important distinguishing clue.

Computed Tomography

Bilateral sacroiliitis. Axial CT scan shows erosions and iliac side subchondral sclerosis of both sacroiliac joints.

Pseudoarthrosis. Reconstructed midsagittal CT image shows an L1-L2 diskovertebral lesion with adjacent sclerosis.

Pseudoarthrosis (same patient as in Image above). Reconstructed posterior coronal CT image shows bilateral posterior element breaks (arrows).

Bilateral facet joint ankylosis. Axial CT scan shows complete fusion of both T12-L1 facet joints.

Dural ectasia. Axial postmyelographic CT scan shows prominent dural ectasia with scalloping of the adjacent vertebra. Partial fusion of the facet joints is noted.

Findings

CT may be useful in selected patients in whom ankylosing spondylitis is suggested and in whom initial sacroiliac joint radiographs findings are normal or equivocal. Features such as joint erosions, subchondral sclerosis (see Image 15), and bony ankylosis are visualized better on CT than on radiographs; however, some normal variants of the sacroiliac joint may simulate the features of sacroiliitis.^10,11,12

CT supplements bone scintigraphy in evaluating areas of increased uptake, particularly in the spine. Bony lesions, such as pseudoarthrosis (see Images 16-17), fractures, spinal canal stenosis, and facet inflammatory disease (see Image 18), are detected well using CT, particularly with reformatted coronal, sagittal, or oblique images. Other useful applications include the assessment of atlantoaxial instability, costovertebral disease, manubriosternal disease, dural ectasia (see Image 19), and paraspinal muscle atrophy.

Multidetector CT (MDCT) is superior to radiographs and MRI in showing more injuries, and it yields more information on fracture morphology. In patients with advanced ankylosing spondylitis, MDCT is the imaging modality of choice for the evaluation of fractures of the cervical spine. It complements MRI, which better shows spinal cord and soft tissue injuries.

Degree of Confidence

Features such as joint erosions, subchondral sclerosis, and bony ankylosis at the sacroiliac joint and the lumbar vertebral facet joints are visualized better on CT scans than on radiographs. CT is accurate for the diagnosis of complications such as spinal pseudoarthrosis, fractures, and vertebral scalloping from dural ectasia.

False Positives/Negatives

On CT, some normal variants of the sacroiliac joint may simulate the features of sacroiliitis.

Magnetic Resonance Imaging

Findings

MRI may have a role in the early diagnosis of sacroiliitis. Detection of synovial enhancement on MRI has been found to correlate with disease activity, as measured by laboratory inflammatory markers. MRI has been found to be superior to CT in the detection of cartilage changes, bone erosions, and subchondral bone changes. MRI is also sensitive for the assessment of activity in relatively early disease. Affected sites include the diskovertebral junction and the peripheral joints. In general, areas of increased T2 signal correlate with the presence of edema or vascularized fibrous tissue.^{13,14,15,16,17,18,19,20,21,22,23}

In established disease, MRI detects pseudoarthrosis, diverticula associated with cauda equina syndrome, and spinal canal stenosis. In patients with complications of fracture or pseudoarthrosis, MRI is useful for the assessment of spinal canal compromise and cord injury (see Images 20-21). MRI may be used to assess the integrity of intervertebral disks and spinal ligaments in cases involving spinal fractures. MRI is considered to be mandatory for patients with neurologic symptoms, especially for those who experience a symptom-free interval and for those who experience neurologic deterioration after established spinal cord injury.

Pseudoarthrosis. Sagittal T1-weighted MRI shows a prominent T11-T12 diskovertebral lesion (arrows) with posterior element involvement (arrowheads).

Pseudoarthrosis (same patient as in Image 20). Sagittal T2-weighted image shows the linear area of high signal intensity extending obliquely from the T11-T12 diskovertebral lesion (arrows) to the posterior elements (arrowheads).

MRI has been found to have a role in monitoring the treatment of patients with active ankylosing spondylitis. The degree of spinal inflammation may be detected before and after therapy with drugs such as the tumor necrosis factor-alpha receptor fusion protein etanercept and the interleukin 1 receptor antagonist anakinra.

Advantages of MRI include direct visualization of cartilage abnormalities, detection of bone marrow edema, improved detection of erosions, and the absence of ionizing radiation.

Degree of Confidence

Yu et al have found MRI to be more sensitive than either radiography or CT in detecting early cartilage changes and bone marrow edema of the sacroiliac joints.²⁴

False Positives/Negatives

Although sensitive in the detection of sacroiliitis, MRI is not specific for diagnosing ankylosing spondylitis as the cause of sacroiliitis.

Nuclear Imaging

Findings

Bone scintigraphy may be helpful for patients with suggested ankylosing spondylitis in whom radiographic findings are normal or equivocal. Qualitative assessment of the accumulation of radionuclides in the sacroiliac region may be difficult because of normal uptake in the location. Quantitative analysis may be more useful in these patients. Ratios of sacroiliac joint to sacral uptake of 1.3:1 or more are considered abnormal (see Image 22).^25,26

Quantitative scintigraphy. Increased sacroiliac joint uptake is seen, with a sacroiliac joint-to-sacral uptake ratio that exceeds 1.7:1 on each side.

Degree of Confidence

Scintigraphy has high sensitivity but low specificity for the diagnosis of sacroiliitis. Several factors potentially affect calculation of the sacroiliac joint to sacrum ratio. These factors include a prominent sacral tubercle that may produce increased uptake in the sacrum and the influence of age and sex on radionuclide uptakes in the sacroiliac joints and sacrum. In patients with advanced disease, the radionuclide uptake may not appear abnormal.

Although sensitive for the detection of active disease in the spine, increased radionuclide accumulation is not specific for the diagnosis of ankylosing spondylitis.

False Positives/Negatives

Abnormal radionuclide uptake in the sacroiliac joints and other spinal locations may not be specific for ankylosing spondylitis. Correlation with other radiologic and clinical findings is important.

Intervention

Medicolegal Pitfalls

• Failure to detect complications in patients with long-standing ankylosing spondylitis is a pitfall. Complications include fracture and pseudoarthrosis. Fractures typically occur in patients with minimal trauma. Pseudoarthrosis is suggested in patients presenting with increasing back pain after a long quiescent period. A high index of clinical suspicion and the application of appropriate imaging is required for accurate diagnosis.

Multimedia

Media file 1: Bilateral sacroiliitis. Frontal radiograph shows bilateral sacroiliac joint erosions and iliac side subchondral sclerosis.

Media file 2: Bilateral chronic sacroiliitis. Frontal radiograph shows complete fusion of both sacroiliac joints.

Media file 3: Romanus lesions. Lateral radiograph shows anterior corner erosions at the T12 and L1 vertebral bodies. The typical shiny corner sign (or Romanus lesion) is present (arrows).

Media file 4: Vertebral body squaring. Lateral radiograph shows squaring of L3 and L4 vertebral bodies, L3-L4 anterior syndesmophyte, and lumbar facet joint fusion.

Media file 5: Interspinous ossification. Frontal radiograph shows T12-L2 lateral syndesmophytes and interspinous ligament ossification extending from the T12 to L1 and L2 to L4 levels.

Media file 6: Vertebral fusion. Lateral radiograph shows solid ankylosis of all cervical facet joints from C2 downwards. Extensive anterior and posterior syndesmophytes is noted.

Media file 7: Bamboo spine. Frontal radiograph shows complete fusion of the vertebral bodies. Extensive facet joint ankylosis and posterior ligamentous ossification produce the trolley track appearance.

Media file 8: Disk calcification. Lateral radiograph shows L2-L3 and L3-L4 disk calcifications, as well as L2-L4 anterior syndesmophytes.

Media file 9: Thoracolumbar junction fracture. Lateral radiograph shows features of established ankylosing spondylitis. A T12 vertebral body fracture is noted, with disruption of the ossified anterior longitudinal ligament (arrow). An old L1 compression fracture is present.

Media file 10: Chalk stick fracture. Lateral radiograph shows a fracture through the ankylosed cervical spine, producing a gap at the C6-C7 disk.

Media file 11: Pseudoarthrosis. Lateral radiograph shows a T11-T12 diskovertebral lesion with adjacent sclerosis (Andersson lesion; arrow). Posterior element defect is present (arrowheads). The patient also has a severe kyphotic deformity.

Media file 12: Pelvic enthesopathy. Frontal radiograph shows ill-defined erosions with adjacent sclerosis at the left ischial tuberosity and more established new bone formation on the right side.

Media file 13: Shoulder enthesopathy. Frontal radiograph shows irregular bony proliferation at the coracoclavicular ligament attachment sites to the inferior clavicle and the superior coracoid process.

Media file 14: Hip joint changes. Frontal radiograph shows uniform joint space narrowing and a collar of osteophytes at the femoral head-neck junction. Left sacroiliac joint ankylosis is present.

Media file 15: Bilateral sacroiliitis. Axial CT scan shows erosions and iliac side subchondral sclerosis of both sacroiliac joints.

Media file 16: Pseudoarthrosis. Reconstructed midsagittal CT image shows an L1-L2 diskovertebral lesion with adjacent sclerosis.

Media file 17: Pseudoarthrosis (same patient as in Image above). Reconstructed posterior coronal CT image shows bilateral posterior element breaks (arrows).

Media file 18: Bilateral facet joint ankylosis. Axial CT scan shows complete fusion of both T12-L1 facet joints.

Media file 19: Dural ectasia. Axial postmyelographic CT scan shows prominent dural ectasia with scalloping of the adjacent vertebra. Partial fusion of the facet joints is noted.

Media file 20: Pseudoarthrosis. Sagittal T1-weighted MRI shows a prominent T11-T12 diskovertebral lesion (arrows) with posterior element involvement (arrowheads).

Media file 21: Pseudoarthrosis (same patient as in Image 20). Sagittal T2-weighted image shows the linear area of high signal intensity extending obliquely from the T11-T12 diskovertebral lesion (arrows) to the posterior elements (arrowheads).

Media file 22: Quantitative scintigraphy. Increased sacroiliac joint uptake is seen, with a sacroiliac joint-to-sacral uptake ratio that exceeds 1.7:1 on each side.

References

1. Bennett DL, Ohashi K, El-Khoury GY. Spondyloarthropathies: ankylosing spondylitis and psoriatic arthritis. Radiol Clin North Am. Jan 2004;42(1):121-34. [Medline].

2. El-Khoury GY, Kathol MH, Brandser EA. Seronegative spondyloarthropathies. Radiol Clin North Am. Mar 1996;34(2):343-57, xi. [Medline].

3. Peh WC. Cervical spine ankylosing spondylitis. Am J Orthop. Jun 2004;33(6):310. [Medline].

4. Wu Z, Lin Z, Wei Q, Gu J. Clinical features of ankylosing spondylitis may correlate with HLA-B27 polymorphism. Rheumatol Int. Feb 2009;29(4):389-92. [Medline].

5. Boonen A, Braun J, van der Horst-Bruinsma IE, Huang F, Maksymowych WP, Kostanjsek N Dr, et al. The ASAS/WHO ICF Core Sets for Ankylosing Spondylitis: how to classify the impact of AS on functioning and health. Ann Rheum Dis. Mar 11 2009;[Medline].

6. Braun J, Sieper J, Bollow M. Imaging of sacroiliitis. Clin Rheumatol. 2000;19(1):51-7. [Medline].

7. Jacobson JA, Girish G, Jiang Y, Resnick D. Radiographic evaluation of arthritis: inflammatory conditions. Radiology. Aug 2008;248(2):378-89. [Medline].

8. Karasick D, Schweitzer ME, Abidi NA, Cotler JM. Fractures of the vertebrae with spinal cord injuries in patients with ankylosing spondylitis: imaging findings. AJR Am J Roentgenol. Nov 1995;165(5):1205-8. [Medline].

9. van der Heijde D, Landewé R, Baraliakos X, Houben H, van Tubergen A, Williamson P, et al. Radiographic findings following two years of infliximab therapy in patients with ankylosing spondylitis. Arthritis Rheum. Oct 2008;58(10):3063-70. [Medline].

10. Geijer M, Sihlbom H, Gothlin JH, Nordborg E. The role of CT in the diagnosis of sacro-iliitis. Acta Radiol. May 1998;39(3):265-8. [Medline].

11. Koivikko MP, Kiuru MJ, Koskinen SK. Multidetector computed tomography of cervical spine fractures in ankylosing spondylitis. Acta Radiol. Nov 2004;45(7):751-9. [Medline].

12. Tan S, Yao J, Ward MM, Yao L, Summers RM. Computer aided evaluation of ankylosing spondylitis using high-resolution CT. IEEE Trans Med Imaging. Sep 2008;27(9):1252-67. [Medline].

13. Baraliakos X, Davis J, Tsuji W, Braun J. Magnetic resonance imaging examinations of the spine in patients with ankylosing spondylitis before and after therapy with the tumor necrosis factor alpha receptor fusion protein etanercept. Arthritis Rheum. Apr 2005;52(4):1216-23. [Medline].

14. Bozgeyik Z, Ozgocmen S, Kocakoc E. Role of diffusion-weighted MRI in the detection of early active sacroiliitis. AJR Am J Roentgenol. Oct 2008;191(4):980-6. [Medline].

15. Erdem CZ, Sarikaya S, Erdem LO, et al. MR imaging features of foot involvement in ankylosing spondylitis. Eur J Radiol. Jan 2005;53(1):110-9. [Medline].

16. Iplikcioglu AC, Bayar MA, Kokes F, et al. Magnetic resonance imaging in cervical trauma associated with ankylosing spondylitis: report of two cases. J Trauma. Mar 1994;36(3):412-3. [Medline].

17. Jee WH, McCauley TR, Lee SH, et al. Sacroiliitis in patients with ankylosing spondylitis: association of MR findings with disease activity. Magn Reson Imaging. Feb 2004;22(2):245-50. [Medline].

18. Kim NR, Choi JY, Hong SH, Jun WS, Lee JW, Choi JA, et al. "MR corner sign": value for predicting presence of ankylosing spondylitis. AJR Am J Roentgenol. Jul 2008;191(1):124-8. [Medline].

19. Levine DS, Forbat SM, Saifuddin A. MRI of the axial skeletal manifestations of ankylosing spondylitis. Clin Radiol. May 2004;59(5):400-13. [Medline].

20. Pedrosa I, Jorquera M, Mendez R, Cabeza B. Cervical spine fractures in ankylosing spondylitis: MR findings. Emerg Radiol. Mar 2002;9(1):38-42. [Medline].

21. Rudwaleit M, Baraliakos X, Listing J. Magnetic resonance imaging of the spine and the sacroiliac joints in ankylosing spondylitis before and during therapy with etanercept. Ann Rheum Dis. Mar 18 2005;[Medline].

22. Tan AL, Marzo-Ortega H, O'Connor P, et al. Efficacy of anakinra in active ankylosing spondylitis: a clinical and magnetic resonance imaging study. Ann Rheum Dis. Sep 2004;63(9):1041-5. [Medline].

23. Vinson EN, Major NM. MR imaging of ankylosing spondylitis. Semin Musculoskelet Radiol. Jun 2003;7(2):103-13. [Medline].

24. Yu W, Feng F, Dion E, et al. Comparison of radiography, computed tomography and magnetic resonance imaging in the detection of sacroiliitis accompanying ankylosing spondylitis. Skeletal Radiol. Jun 1998;27(6):311-20. [Medline].

25. Peh WC, Ho WY, Luk KD. Applications of bone scintigraphy in ankylosing spondylitis. Clin Imaging. Jan-Feb 1997;21(1):54-62. [Medline].

26. Taylor HG, Gadd R, Beswick EJ, et al. Quantitative radio-isotope scanning in ankylosing spondylitis: a clinical, laboratory and computerised tomographic study. Scand J Rheumatol. 1991;20(4):274-9. [Medline].

27. Ahn NU, Ahn UM, Nallamshetty L, Springer BD, Buchowski JM, Funches L, et al. Cauda equina syndrome in ankylosing spondylitis (the CES-AS syndrome): meta-analysis of outcomes after medical and surgical treatments. J Spinal Disord. 2001;14:427-33.

28. 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. May 2005;64(5):730-4. [Medline].

29. Emery RJ, Ho EK, Leong JC. The shoulder girdle in ankylosing spondylitis. J Bone Joint Surg Am. Dec 1991;73(10):1526-31. [Medline].

30. Ginsburg WW, Cohen MD, Miller GM, Bartleson JD. Posterior vertebral body erosion by arachnoid diverticula in cauda equina syndrome: an unusual manifestation of ankylosing spondylitis. J Rheumatol. Jul 1997;24(7):1417-20. [Medline].

31. Langlois S, Cedoz JP, Lohse A, et al. Aseptic discitis in patients with ankylosing spondylitis: a retrospective study of 14 cases. Joint Bone Spine. May 2005;72(3):248-53. [Medline].

32. Mitchell MJ, Sartoris DJ, Moody D, Resnick D. Cauda equina syndrome complicating ankylosing spondylitis. Radiology. May 1990;175(2):521-5. [Medline].

33. Nakstad PH, Server A, Josefsen R. Traumatic cervical injuries in ankylosing spondylitis. Acta Radiol. Apr 2004;45(2):222-6. [Medline].

34. Ozgocmen S, Ardicoglu O. Odontoid fracture complicating ankylosing spondylitis. Spinal Cord. Feb 2000;38(2):117-9. [Medline].

35. Peh WC, Chu FS, Ho TK. Case of the month: a nasty shock on awakening. Br J Radiol. Nov 1994;67(803):1141-2. [Medline].

36. Peh WC, Ho EK. Fracture of the odontoid peg in ankylosing spondylitis: case report. J Trauma. Mar 1995;38(3):361-3. [Medline].

37. Peh WC, Ho TK, Chan FL. Case report: pseudoarthrosis complicating ankylosing spondylitis-- appearances on magnetic imaging. Clin Radiol. May 1993;47(5):359-61. [Medline].

38. Peh WC, Luk KD. Pseudoarthrosis in ankylosing spondylitis. Ann Rheum Dis. Mar 1994;53(3):206-10. [Medline].

39. Rasker JJ, Prevo RL, Lanting PJ. Spondylodiscitis in ankylosing spondylitis, inflammation or trauma? A description of six cases. Scand J Rheumatol. 1996;25(1):52-7. [Medline].

40. Toussirot E, Benmansour A, Bonneville JF, Wendling D. Atlantoaxial subluxation in an ankylosing spondylitis patient with cervical spine ossification. Br J Rheumatol. Feb 1997;36(2):293-5. [Medline].

41. Wu CT, Lee ST. Spinal epidural hematoma and ankylosing spondylitis: case report and review of the literature. J Trauma. Mar 1998;44(3):558-61. [Medline].

Keywords

ankylosing spondylitis, spondylitis, spondyloarthritis, spondyloarthropathy, rheumatoid spondylitis, bony ankylosis, vertebral inflammation, seronegative arthritis, sacroiliac, facet joint, paravertebral soft tissue, peripheral arthritis, iritis

Contributor Information and Disclosures

Author

Wilfred CG Peh, MD, MBBS, FRCP(Glasg), FRCP(Edin), FRCR, Clinical Professor, Faculty of Medicine, National University of Singapore; Senior Consultant Radiologist, Alexandra Hospital, Singapore
Wilfred CG Peh, MD, MBBS, FRCP(Glasg), FRCP(Edin), FRCR is a member of the following medical societies: American Roentgen Ray Society, British Institute of Radiology, International Skeletal Society, Radiological Society of North America, Royal College of Physicians, and Royal College of Radiologists
Disclosure: Nothing to disclose.

Medical Editor

Michael A Bruno, MD, Associate Professor, Departments of Radiology and Medicine, Pennsylvania State University College of Medicine; Director, Radiology Quality Management Services, Milton S Hershey Medical Center, Pennsylvania State University College of Medicine
Michael A Bruno, MD is a member of the following medical societies: American College of Radiology, American Roentgen Ray Society, Association of University Radiologists, Radiological Society of North America, Society of Nuclear Medicine, and Society of Skeletal Radiology
Disclosure: Nothing to disclose.

Pharmacy Editor

Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand
Disclosure: Nothing to disclose.

Managing Editor

Wilfred CG Peh, MD, MBBS, FRCP(Glasg), FRCP(Edin), FRCR, Clinical Professor, Faculty of Medicine, National University of Singapore; Senior Consultant Radiologist, Alexandra Hospital, Singapore
Wilfred CG Peh, MD, MBBS, FRCP(Glasg), FRCP(Edin), FRCR is a member of the following medical societies: American Roentgen Ray Society, British Institute of Radiology, International Skeletal Society, Radiological Society of North America, Royal College of Physicians, and Royal College of Radiologists
Disclosure: Nothing to disclose.

CME Editor

Robert M Krasny, MD, Consulting Staff, Department of Radiology, Resolution Imaging Medical Corporation
Robert M Krasny, MD is a member of the following medical societies: American Roentgen Ray Society and Radiological Society of North America
Disclosure: Nothing to disclose.

Chief Editor

Felix S Chew, MD, MBA, EdM, Professor, Department of Radiology, Vice Chairman for Radiology Informatics, Section Head of Musculoskeletal Radiology, University of Washington
Felix S Chew, MD, MBA, EdM is a member of the following medical societies: American Roentgen Ray Society, Association of University Radiologists, and Radiological Society of North America
Disclosure: Nothing to disclose.

Related eMedicine topics

Ankylosing Spondylitis and Undifferentiated Spondyloarthropathy (from Rheumatology)

Ankylosing Spondylitis (from Neurology)

Rheumatoid Spondylitis

Clinical guidelines

Adalimumab, etanercept and infliximab for ankylosing spondylitis. National Institute for Health and Clinical Excellence (NICE) - National Government Agency [Non-U.S.].  2008 May.  47 pages.  NGC:006523 
 

Clinical trials

Efficacy of AIN457 in Adults (18-65 Years) With Moderate to Severe Ankylosing Spondylitis

Study Evaluating Etanercept for the Treatment of Active, Severe, and Advanced Axial Ankylosing Spondylitis

Examination of Radiographic Progression, Efficacy and Safety of Long-Term Treatment With Infliximab in Patients With Ankylosing Spondylitis

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