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. Over 95% of Caucasian patients with AS are HLA B27-positive, compared to only 50% of people of African descent.
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 15 and 40 years. However, younger and older people can also be affected.
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
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.
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)
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
Making the Diagnosis
Your doctor will make the diagnosis of AS based on your symptoms and an X-ray or another type of imaging of your affected joints. The earliest sign is sacroiliitis (inflammation of the sacroiliac joint). It can be seen on an X-ray of the pelvis, or it can be detected at an even earlier stage with a MRI scan.
If you have AS, the X-ray will show areas where the bone has been worn away by the condition. The vertebrae of the spine may start to fuse together because the ligaments between them become calcified. The term for bones growing together due to inflammation is ankylosis, and this is where the name ankylosing spondylitis comes from. ("Spondyl" refers to the spine and "itis" means inflammation.) A physical exam for AS includes the Schober test to assess the flexibility of the spine, which can be abnormal even when it's not obvious to the person.
Your doctor may also do a blood test called erythrocyte sedimentation rate (ESR) or a C-reactive protein test (CRP). A high ESR or CRP is a sign of conditions with inflammation, such as AS. However, it does not definitely mean that you have AS, since many other conditions can also cause a high ESR or CRP, and two-thirds of people with AS have a normal ESR.
Since back pain and osteoarthritis are common and AS comes on gradually, there is often a long delay in recognizing AS, especially among doctors who are not specialized in rheumatology (the study and treatment of arthritis and other diseases that affect joints, muscles, and bones).
Treatment and Prevention
Currently, there is no cure for AS, but it can be managed using medications, surgery, and physiotherapy.
Rheumatologists are the most specialized and experienced doctors in the diagnosis and management of AS and other spondylopathies.
Nonsteroidal anti-inflammatory drugs (NSAIDs; e.g., ibuprofen*, naproxen) work by reducing inflammation, which helps relieve the pain, stiffness, and swelling of AS. They do not slow down the progression of the condition; in other words, they don't stop the disease from getting worse. Possible side effects of NSAIDs include nausea, abdominal pain, asthma, liver damage, heart problems, high blood pressure, stomach ulcers, and bleeding.
Corticosteroids (e.g., prednisone, triamcinolone, methylprednisolone) work by reducing inflammation. They are used to relieve symptoms but do not affect spinal changes. Corticosteroids do not slow down the progression of the condition. They may be injected into an affected joint or taken by mouth. Side effects of the injection include joint damage (if the injection is used too often) and infection. Short-term side effects of the pills include increased appetite, weight gain, menstrual changes, emotional changes, and stomach irritation. Long-term use of high doses can lead to diabetes, cataracts, glaucoma, increased risk of serious infection, high blood pressure, osteoporosis (bone thinning), moon face (rounding of the face), mood changes, acne, joint damage, reactivation of hidden infections, muscle weakness, or increased body hair.
Biologics, (e.g., adalimumab, etanercept, golimumab , infliximab) are used to relieve signs and symptoms of the condition, including symptoms in the spine. Some biologics can also help to improve physical function for people with AS. They can slow or stop the progression of the disease, but they may not work for everyone. They work by neutralizing a molecule called tumour necrosis factor alpha (TNF-α), which is involved in causing inflammation. Biologics are given as an injection under the skin (a subcutaneous injection) or as an injection into the vein over a period of time (an intravenous infusion). Possible side effects include infusion reactions (e.g., rash, flushing, headache, and difficulty breathing), irritation at the injection area, nausea, headache, vomiting, diarrhea, fatigue, joint pain, or an increased risk of serious infection (including brain infection). There have also been reports of multiple sclerosis and systemic lupus erythematosus.
Disease modifying antirheumatoid drugs (DMARDs; e.g., methotrexate) are used to relieve AS symptoms and slow down the progression of the condition. DMARDs may be beneficial to people with peripheral AS (AS that involves other joints). They do not relieve inflammation in the spine. Possible side effects include nausea, diarrhea, increased risk of infections, liver damage, lung damage, and bleeding.
Make sure you understand and discuss all the risks and benefits of taking any medications before you start them.
Surgery may be used to repair joint damage or replace damaged areas. For example, some people with AS may need a hip replacement.
A physiotherapist can show you special exercises to improve your flexibility, strength, and mobility. If the disease is not slowed or stopped, regular exercise and supervised physical therapy are essential to maintain a working posture once the spine becomes fused - it is far better to be stiff upright than bent over.
*All medications have both common (generic) and brand names. The brand name is what a specific manufacturer calls the product (e.g., Tylenol®). The common name is the medical name for the medication (e.g., acetaminophen). A medication may have many brand names, but only one common name. This article lists medications by their common names. For information on a given medication, check our Drug Information database. For more information on brand names, speak with your doctor or pharmacist.
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