In its advanced stages, ankylosing spondylitis (AS) can lead to a condition that is sometimes called bamboo spine. AS, a type of axial spondyloarthritis, is an autoimmune disease that can lead to inflammatory back pain (especially in the lower back), as well as back stiffness and decreased flexibility in the spine. About 1 in every 200 to 500 people in the United States are living with AS.
To understand bamboo spine, it helps to understand the components of a healthy spine. Your spine is a stacked column of 33 bones called vertebrae that surround and protect your spinal cord (the bundle of nerves that sends signals between your body and your brain). Between vertebral bodies are flexible discs called intervertebral discs that cushion the vertebrae and allow for flexion in the spine. The vertebrae are also supported by ligaments that prevent you from overbending your back.
In people with ankylosing spondylitis, some of these structures develop abnormalities. "Ankylosis" refers to the fusion of bones, and "spondylitis" means "inflammation and disease of your spine."
Your body’s immune system is normally supposed to help you fight off infections by outside invaders like bacteria and viruses. In AS, your immune system can end up attacking your body. When this autoimmune process affects your spine, chronic cycles of inflammation and repair can sometimes cause your vertebrae to fuse together by slowly turning the normally flexible ligaments and discs to hard bone. This process is called ossification. Ossification and the resulting ankylosis — bone fusion — gradually makes your back very stiff and causes you to lose flexibility over time. Because the ankylosed spine resembles a stalk of bamboo on imaging tests like X-rays, this feature of AS has earned the nickname bamboo spine.
AS-related back pain usually starts in your sacroiliac joints, which connect your lower back with your hips. Inflammation in these joints is called sacroiliitis. You may notice buttock or hip pain before the pain works its way up to the lower back (lumbar spine) and then eventually the mid-back (thoracic spine) and upper back (cervical spine).
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The back pain may come on as morning stiffness, which is most painful in the morning right after you wake up. The stiffness typically gets better as you move around. This aspect differentiates AS from osteoarthritis and non-autoimmune causes of back pain, which tend to be milder in the mornings and worse with activity.
People with ankylosing spondylitis have an increased risk of spinal fractures, as fused backbones are much more likely to break when bending. Without treatment, the back may eventually become deformed and lose its normal curvature, which is called kyphosis. Long-standing autoimmune damage may cause the inside of the vertebrae and other bones in the body to become softer and more brittle (osteoporosis), which also increases the risk of fractures.
Doctors diagnose AS by using clinical criteria (your symptoms and their physical exam) in addition to radiographic imaging (what the doctors see on scans). Because the term bamboo spine refers to abnormalities seen on X-ray (also called a radiograph), radiography will typically be part of the series of imaging and tests you'll undergo to determine if you have developed bamboo spine from AS. If fusion of the spine cannot be seen on X-ray, an MRI may be needed to see if there is sacroiliitis or inflammation within the vertebrae.
Treatment of ankylosing spondylitis might involve seeing different providers, including a rheumatologist who can help with medication and a physical therapist who can help with appropriate movements and exercises. Exercise may help people with AS control their pain, improve their strength, and prevent worsening of their condition.
There are two types of medications that are used to treat AS: those that you take for pain and flares and those you take long-term to control and prevent progression of AS, which may help to avoid bamboo spine.
Nonsteroidal anti-inflammatory drugs (NSAIDs) can be used for pain episodes and are the first-line medication especially for people with milder forms of AS. NSAIDs include popular over-the-counter drugs like Advil (ibuprofen) or Aleve (naproxen).
For people with more severe forms of AS, biologic therapies may be taken regularly to help stop the progression of AS. Many of these drugs target a certain protein called tumor necrosis factor (TNF), which is involved in many autoimmune conditions. Common TNF inhibitor drugs include Humira (adalimumab) and Remicade (infliximab). Other biologic drugs include interleukin-17 inhibitors like Cosentyx (secukinumab).
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