ANKYLOSIS SPONDYLITIS

RADIOLOGY ASPECT

Radiographs (plain x-ray films) are the single most important imaging technique for detection, diagnosis, and follow-up monitoring of patients with ankylosing spondylitis. Overall, x-ray films can well depict bony features, subtle deposits of calcium in tissue, and areas of tissue that are hardening into bone. The doctor can reliably diagnose ankylosing spondylitis if its typical radiographic features are present.

Radiographic findings are as follows:

• Sacroiliitis (inflammation of the sacroiliac joints at the base of the spine) 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. Bony erosions on sides of the joint develop, with eventual bony fusion. Sacroiliitis occurs typically in a symmetric pattern.

• In the spine, the early stages of spondylitis develop as small erosions at the corners of the vertebral bodies. This is followed by syndesmophyte formation (ossification [bone formation] of the outer fibers of the annulus fibrosis [fibrocartilaginous material that surrounds the intervertebral disk]). This causes the corners of one vertebra to bridge to another. The complete fusion of the vertebral bodies by syndesmophytes and other related ossified soft tissues produces the so-called bamboo spine.

• Fractures in established ankylosing spondylitis usually occur at the thoracolumbar and cervicothoracic junctions. Fractures typically extend front to back and frequently pass through the ossified disk. These fractures have been termed chalk stick fractures.

• On the x-ray film, pseudoarthrosis (an abnormal union formed by fibrous tissue within a fracture) appears as areas of diskovertebral destruction and adjacent hardening. Pseudoarthrosis usually develops secondarily to a previously undetected fracture or at an unfused segment but may be mistaken for a disk infection. An important distinguishing imaging feature is the involvement of the posterior elements.

• On the x-ray film, enthesopathy (inflammation where ligaments, tendons, and joint capsules attach to bone) appears as erosions at the sites of attachments. With healing, new bone proliferation occurs. Lesions typically develop bilaterally (on both sides) and are symmetric in distribution. Enthesopathic changes are particularly prominent at certain sites around the pelvis.

• Hip joint involvement is typically bilateral and symmetric. The hip joint space is narrowed uniformly, and the head of the femur (thigh bone) moves inward. Subsequently, the head of the femur protrudes into the pelvis or bony ankylosis.

• Ankylosing spondylitis can affect the lung in the form of progressive fibrosis (fibrous degeneration) and lesion changes at the tops of the lungs. On x-ray films, chest lesions may resemble tuberculous infection. Infections involving Aspergillus species and other opportunistic infections may complicate lung bullae (lesions). Ankylosing spondylitis usually affects the lungs several years after the disease affects the joints.

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.

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).

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).

Ankylosing spondylitis has a predilection for the axial skeleton, affecting particularly the sacroiliac and spinal facet joints and the paravertebral soft tissues. Extraspinal manifestations of the disease include peripheral arthritis, iritis, pulmonary involvement, and systemic upset.^1,2,3

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.

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.

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

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.

More examples of X-ray:













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