Ankylosing Spondylitis
In this condition factsheet:
The Facts on Ankylosing Spondylitis
Ankylosing spondylitis (AS) is a type of arthritis that causes inflammation in the joints of the spine. The most common areas affected are the sacroiliac joints, which are the joints at the base of the spine that connect the spine and the pelvis, as well as the joints between the vertebrae. Other joints, such as the hips and shoulders, may also be similarly affected. AS causes pain, stiffness, and inflammation at the affected joints.
AS is the most common of the arthritis conditions known as spondylopathies. The second most common spondylopathy occurs in people with psoriasis.
About 1% of Canadians have AS. Having a family member with AS increases your risk of developing the condition, since the disease is at least partly hereditary. People with a certain molecule called HLA B27 on the surface of their cells are also more likely to get AS. Having both HLA B27 and a family history further increases your risk if a first-degree relative (e.g., a parent) has it. However, if you carry this molecule without a family history, the chance of getting this condition is lower. 90% of Caucasian patients with AS are HLA B27-positive, although it is present in up to 10% of the general population. There is also thought to be an environmental risk, since if one identical twin has AS there is only a 50% chance that the other will have it.
AS affects about three times as many men as women, but it may be that the disease is less recognized among women. Most people are first diagnosed between the ages of 20 and 40 years. However, younger and older people can also be affected.
Causes of Ankylosing Spondylitis
The cause of AS is not completely understood, but it's believed to be at least partly related to genetics. AS is more common in people with a family history of the condition. One theory is that AS is "triggered" by something in the environment, such as an infection, for people whose genes put them at risk of AS. The immune system responds to this trigger by producing chemicals that cause inflammation in the spine and other joints of the body. There is no evidence, however, that an infection causes the disease.
It is also known that people with a molecule called HLA B27 on the surface of their cells are at higher risk of developing AS. HLA B27 can be passed down from parent to child. Although it increases the risk of AS, not everyone with HLA B27 will get AS.
Symptoms and Complications of Ankylosing Spondylitis
AS can cause a variety of different symptoms, but most people with AS have low back pain and stiffness. The stiffness is often worst in the morning and after you have been inactive for a while. The back pain and stiffness can prevent you from moving around comfortably and getting a good night's sleep.
Most people with other kinds of low back pain feel better after a night's rest, but a hallmark of AS is that people usually feel worse and stiffer in the morning after sleeping. The involvement of the spine is called axial; involvement of other joints is termed peripheral. Most people will have mainly axial involvement.
Other joints can also become affected by AS, such as the hips, shoulders, and knees. The involvement of the spine is called axial; involvement of other joints is termed peripheral. People with AS can experience fatigue, weight loss, and loss of appetite. The symptoms of AS tend to come and go, with periods of no symptoms followed by flare-ups.
AS can cause complications both in the joints and elsewhere in the body, including:
- bent-over or unusually straight posture
- limited mobility (ability to move around)
- eye inflammation (uveitis, which can cause eye pain, irritation, and sensitivity to light and requires immediate medical attention)
- breathing problems due to stiffness in the joints between the spine and the ribs
- arthritis and sometimes significant damage to hip and shoulder joints (and occasionally to other joints)
- inflammation in places where ligaments and tendons attach to the bone (called enthesitis)
- anemia
- low-grade fever
- fatigue
- loss of appetite and weight loss
Very rare complications can include:
- inflammation of the aorta, a large blood vessel that brings blood from the heart to the rest of the body, and secondary aortic valve insufficiency (when the aortic valve is weakened, preventing the valve from closing properly)
- spinal cord injury due to fractures (breaks) in the spine
- cauda equina syndrome, where AS damages the nerves at the base of the spinal cord, leading to loss of sensation in the buttocks, rectum, thighs, and bladder; or loss of bowel or bladder control
