Ankylosing Spondylitis: Description and Diagnosis
What Is It?
Ankylosing Spondylitis (AS) is a chronic inflammatory disease characterized by pain and progressive stiffness. It is part of a group of rheumatic diseases termed seronegative spondyloarthropathies (vertebral joints) that share the human antigen HLA-B27. Ankylosing spondylitis is seronegative (serum negative) because a rheumatoid factor is not detected in the patient's blood (serum).
Ankylosing spondylitis is considered to be hereditary, although environmental factors have been suggested. Most people with the HLA-B27 antigen do not develop AS. It is known to affect white males about four times as often as females. Onset typically occurs between the ages of 15 and 45.
In the early stages of the disease, the sacroiliac joints (back of the pelvis) become inflamed and painful. As the disease progresses, ossification is triggered by the body's defense mechanism. Ossification causes new bone to grow between vertebrae eventually fusing them together increasing the risk for fracture. Further, ossification may affect spinal ligaments causing spinal canal stenosis (narrowing), which can result in neurologic deficit.
Other symptoms may include:
- Low back pain that may spread down into the buttocks and thighs. Pain varies in intensity, duration, and is episodic. Stiffness is usually worse in the morning and improves with exercise.
- Limited motion in the lumbar spine.
- As the disease progresses, the patient may notice the discomfort moves up the spine.
- The thoracic region may be affected by pain, stiffness, and limited chest expansion.
- Pain, tenderness, and stiffness in the shoulders, hips, knees, and heels.
- Cauda Equina Syndrome (specific nerve compression) may develop causing bilateral lower extremity numbness, weakness, and incontinence.
- Inflammation of the intervertebral disc or disc space (spondylodiscitis) is a common complication caused by the hardening/thickening of fibrous tissue (sclerosis) affecting vertebral end plates. The resultant abnormal vertebral motion almost always causes pain.
- Spinal deformity: kyphosis (humpback), lordosis (swayback).
General health and family medical history is important because ankylosing spondylitis can be hereditary. Ankylosing spondylitis may or may not be associated with nonskeletal diseases such as uveitis (eye inflammation), prostatitis (prostate inflammation) and certain disorders affecting cardiac and pulmonary function. A blood workup will reveal the HLA-BA27 antigen. A physical examination often includes the following:
Schober Test: Limited motion in the lumbar spine is symptomatic of AS. The Schober test measures the degree of lumbar forward flexion as the patient bends over as though touching their toes. Progressive loss of spinal motion is correlated with x-ray findings.
Gaenslen Test: Sacroiliac pain is often found in the early stage of AS. Gaenslen's maneuver stresses the sacroiliac joints. Increased pain during this maneuver could be indicative of joint disease.
When ankylosing spondylitis affects the thoracic spine normal chest expansion may be compromised. The amount of chest expansion is measured from deep expiration to full inspiration. Measurements significantly less than one inch (normal chest expansion) could indicate AS.
General range of motion measures the degree to which a patient can perform movements of flexion, extension, lateral bending, and spinal rotation. Asymmetry may also be noted.
A neurologic evaluation is mandatory for patients presenting with a spine disorder. The following symptoms are assessed: pain, numbness, paresthesias (e.g. tingling), extremity sensation, and motor function, muscle spasm, weakness, and bowel/bladder changes.
Plain radiographs (x-rays) are standard for AS. A CT Scan or MRI may be ordered to evaluate bone and soft tissues (eg, spinal canal) in greater detail. These tests reveal changes in the spine affected by AS.
Characteristic bilateral sacroiliac changes may appear as blurry erosions (wearing away) or hardening/thickening of fibrous tissue (sclerosis) on either side of the joint(s).
Loss of cartilage spacing in the facet joints, which fuse and become indistinguishable.
Natural spinal curvature lost and presentation of abnormal kyphosis (humpback) and/or lordosis (swayback).
Spinal fractures anywhere in the spinal column. A CT Scan or MRI may detect epidural bleeding common following spinal fracture. This bleeding may cause a semisolid swelling (hematoma) causing compression of neural elements. Fractures may lead to neurologic deficit and/or spinal deformity.
Lumbar vertebrae may appear abnormally square from erosion that has occurred where bone meets fibrous tissue during the inflammatory phase.
'Bamboo Spine' is typical of ankylosing spondylitis and results from ossification of the annulus fibrosus, the anterior longitudinal ligament, and bony bridges that form across the intervertebral spaces.