Ankylosing spondylitis (AS) is the advanced form of axial spondyloarthritis, a type of autoimmune arthritis that affects the spine and hip bones. Andersson lesions are an unusual type of damage to the spine caused by AS that destroys weight-bearing intervertebral joints and causes spinal fractures.
Andersson lesions are a type of damage to the spine seen in some people with advanced AS (also called radiographic axial spondyloarthritis). Andersson lesions have been called many different names, including discovertebral lesions and spondylodiscitis.
It is not known how common Andersson lesions are — various studies have reported their prevalence as anywhere from 1.5 percent to 28 percent in people with AS.
Andersson lesions are caused by damage to the weight-bearing intervertebral joints of the spine. These joints are made up of vertebral bodies (the large, thick part of spinal bones) and the intervertebral disc (the rubbery soft tissue that acts as a cushion between vertebral bodies). Ligaments hold the joint together, connecting the vertebral bodies and anchoring the intervertebral disc in place.
The hallmark of AS is the abnormal growth of bone that results in ankylosis, or the fusion of the sacroiliac joints (which connect the hips and spine) and vertebrae in the spine. AS causes bone to grow between vertebrae, fusing them together. Between vertebral bodies, bone grows and connects vertebrae together around the edge of the intervertebral disc, locking the disc in place.
Andersson lesions occur when there is destruction of the bone above or below a disc. The lesions may also involve destruction of the disc itself. This destruction can lead to back pain and neurological symptoms caused by pressure on the spinal cord and the nerves that branch off of the spinal cord.
The damage can also lead to spinal pseudoarthrosis, a “break” in ankylosed spine that has been fused together by AS. In addition to pain, pseudoarthrosis can cause abnormal mobility and instability in the spine.
Andersson lesions can occur anywhere in the spine, including the cervical spine in the neck or the thoracolumbar spine in the chest and lower back. Destructive lesions can occur at a single intervertebral joint or affect multiple joints in the spine. Sometimes, joint destruction leads to exaggerated kyphosis (forward curvature of the thoracic spine) or lordosis (backward curvature of the lumbar spine).
Andersson lesions are sometimes asymptomatic, but the usual symptoms include localized back pain and spine instability. Pressure on the spinal cord or spinal nerves can sometimes cause neurological symptoms (symptoms that affect the nerves) such as:
Depending on where the lesions occur, they can also cause autonomic dysfunction. The autonomic nervous system controls blood pressure, bowel function, bladder function, sexual function, and other involuntary bodily functions. Dysfunction of the autonomic system can be life-threatening in rare cases.
Andersson lesions are diagnosed using imaging techniques such as X-rays, computed tomography scans, and magnetic resonance imaging (MRI).
X-rays of the spine can show abnormalities in the vertebrae that can include:
There is some dispute over the etiology (underlying causes) of Andersson lesions. Recent research has grouped Andersson lesions into inflammatory and noninflammatory lesions. It is believed that Andersson lesions begin due to inflammation in the intervertebral joints and later progress to noninflammatory lesions.
Inflammation can cause hardening of the outside of the bone. Early on, this inflammation does not cause any changes that can be seen on X-rays, but the inflammatory lesions can be seen using an MRI.
Eventually, inflammation leads to degeneration of the vertebrae, hollowing out the flat parts of the bone that support the body’s weight. These changes can be seen on an X-ray. Over time, discitis (inflammation) causes the disc to degenerate and eventually disappear.
Osteoporosis (loss of bone mass) seen with spondylitis also contributes to Andersson lesions by making bone tissue weaker and more brittle. Ultimately, the lesions result in weak and brittle bone in the vertebrae as well as the bony growths that fuse the vertebrae. This brittle bone is very prone to fractures and stress fractures (chronic microfractures).
Noninflammatory lesions — which include pseudoarthrosis (spinal fracture) and may involve kyphosis (abnormal curvature of the spine) — may be caused by trauma or stress fractures.
Treatment for Andersson lesions depends on the severity of symptoms and whether the lesions are inflammatory or more advanced.
Inflammatory lesions can be treated with medications, such as nonsteroidal anti-inflammatory drugs, as well as rest, braces, and physical therapy.
Andersson lesions generally respond well to treatment. Studies have shown that spinal fusion surgery is very effective for improving pain and other symptoms.
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