Ankylosing spondylitis (AS) is a form of arthritis that mainly affects the spine, lower back, and sacroiliac joints.
AS is an inflammatory condition. Characteristic symptoms include joint pain, stiffness, and a loss of mobility in the spine and lower back.
The condition involves inflammation where the ligament and tendons attach to the bones of the spine and to bones of the peripheral joints, which are known as the entheses.
This inflammation results in increased bone formation in the spine, leading to bone fusion. In advanced cases, this can also lead to spinal deformity.
Drug treatments and physical therapy can help relieve the symptoms.
This article will take a close look at AS, including the symptoms, treatments, causes, and exercises associated with it.
AS is a type of arthritis. It mostly affects the lower part of the spine and the place where the spine joins to the hips, known as the sacroiliac joints.
Males are more likely to develop AS than females. The condition tends to be milder when it does occur in females, which also makes it harder to diagnose.
According to the Spondylitis Association of America, symptoms usually begin between the ages of 17 and 45 years. However, they can also develop in children and people who are much older.
There is currently no cure for AS, but certain drugs can help manage the pain and inflammation. Physical therapy can also relieve pain and prevent or delay limitations and decreased mobility.
The most common early symptoms of AS are pain and stiffness in the lower back, the hip area, or both. These symptoms may occur over the course of several weeks or months.
Over time, these symptoms may spread to other areas of the spine and can affect the spinal joints of the neck.
Some people have mild pain that comes and goes, while others have severe, long lasting pain. Everyone with AS is likely to experience flares, which is when the symptoms worsen, and periods of remission, which is when the symptoms improve.
The main symptoms of AS affect the spine and lower back, causing:
- a loss of mobility
The pain is usually worse during rest and during the night, and it can interfere with restorative sleep. Moving around can generally improve pain levels.
However, the inflammation and pain are not confined to the spine. AS can also affect other parts of the body. These include the areas around other joints, such as the:
- ankles, feet, and tendon insertions at the heel
- top of the shin bone in the lower leg
- Achilles tendon
AS can cause bony fusion, or ankylosing, which refers to an overgrowth of bones at the joints. This can make it difficult to carry out everyday tasks. In some cases, it can also restrict the movement of the chest and make it hard to breathe.
AS is a systemic condition. People can experience constitutional symptoms of fatigue, which refers to a feeling of being tired and lacking energy.
AS can also affect the eyes, causing pain and redness. Without treatment, this inflammation, known as iritis or uveitis, can impair vision.
Other systemic complications and signs of the condition may include neurological, cardiovascular, and pulmonary changes.
The neurologic symptoms can include:
- neuropathy, or nerve symptoms
- myopathy, or muscle problems
- radiculopathy, or pinched nerves
The cardiovascular system effects can involve:
- inflammation of the aorta
- aortic valve disease
- ischemic heart disease
Lung or pulmonary involvement can cause interstitial lung disease, fibrosis, and difficulty breathing due to chest wall restriction that the ankylosing of joints in the spine causes.
Below is a fully interactive 3D model of AS. Explore the model using your mouse pad or touchscreen to learn more about AS.
There is currently no cure for AS, and the damage it causes is irreversible. However, some options can help relieve the symptoms and manage the progression.
- physical therapies and exercises
- certain drugs
- surgery, in rare cases
People with a diagnosis of AS will need to see a specialist doctor known as a rheumatologist. They may need a number of visits, as the condition progresses slowly and consistent medical care allows better monitoring and treatment.
Two common approaches that help people manage AS are drugs, to reduce pain and inflammation, and physical therapy and exercises, to maintain movement and posture.
Doctors will only recommend surgery to correct severe deformity, such as excessive posture changes due to inflammation and ankylosing of the spine, or to replace a hip or other joint.
Doctors might also recommend certain diets, foods, or nutrients to help a person manage the symptoms of AS. Learn more about diet and AS here.
The main drugs that people use to ease the pain and inflammation of AS are nonsteroidal anti-inflammatory drugs (NSAIDs). Some examples of these include ibuprofen, naproxen, and diclofenac.
Acetaminophen and codeine are also options if NSAIDs are unsuitable or ineffective.
Some NSAIDs compromise bone health by reducing the creation of new bone, so doctors do not usually recommend NSAIDs after surgery for people with bone fusion problems.
Some other drug options include:
- local injections of corticosteroids
- disease-modifying antirheumatic drugs, such as sulfasalazine (Azulfidine, Sulfazine) and methotrexate (Otrexup, Rheumatrex, or Trexall)
- tumor necrosis factor antagonists, such as adalimumab (Humira), certolizumab (Cimzia), etanercept (Enbrel), golimumab (Simponi), or infliximab (Remicade)
- other biologic treatments, such as secukinumab (Cosentyx)
AS can affect the whole body, and a person may require coordination of care by a number of specialists, including physical therapists, eye specialists, cardiologists, neurologists, and gastroenterologists.
To diagnose AS, a doctor will ask about the person’s symptoms, carry out a physical examination, and arrange for tests, when necessary.
If inflammatory back pain is present with certain features, it may indicate AS.
These features include:
- pain that does not improve with rest
- pain that causes sleep disturbance
- back pain that starts gradually, between the ages of 17 and 45 years, and is not due to injury
- symptoms that persist for several months
- spinal stiffness in the mornings, which seems to improve with exercise and motion
Imaging tests for AS may confirm the diagnosis, but changes may not be immediately visible on such tests. This can delay diagnosis.
The sections below will look at blood tests and imaging tests in more detail.
No blood test can confirm AS, but there are tests that can rule out other causes of the person’s symptoms.
Genetics are an important feature of this condition. A reported 90% of people with AS have a genetic marker called HLA-B27. Doctors may order a blood test for this as a part of the initial workup.
The tests for inflammation may include:
- erythrocyte sedimentation rate
- C-reactive protein
- complete blood count
If the doctor suspects another cause, such as rheumatoid arthritis, they may test for rheumatoid factor, cyclic citrullinated peptide, and antinuclear antibodies to help rule it out.
These may include:
- X-rays, which can reveal both early and more advanced changes to the spine and pelvis
- CT scans, which create more reliable, higher resolution images than X-rays
- MRI scans, such as an MRI of the sacroiliac joints, which can reveal early signs of the condition
The exact cause of AS remains unclear, but the early symptoms result from inflammation in parts of the lower spine.
With new bone growth as a result of the inflammation, permanent damage and fusion can occur.
However, doctors do not yet know why this chronic inflammatory process occurs in people with AS.
That said, the condition often runs in families. It is possible that AS has both genetic and environmental components.
Physical therapy and exercises can help treat the symptoms and prevent or delay mobility limitations.
A physical therapist will be able to design a program that can help a person maintain good posture and motion in the joints.
This might consist of:
- daily exercises
- special training to address areas of involvement
- therapeutic exercises
Physical therapy exercises are known as strengthening exercises and range-of-motion exercises.
The Spondylitis Association of America say that an ideal exercise program will include the following four elements:
- Stretching: This can improve flexibility and reduce muscle stiffness, swelling, and pain. It can also minimize the risk of joint fusion.
- Cardiovascular exercises: These exercises, which include swimming and walking, can improve lung and heart function and reduce pain and fatigue.
- Muscle exercises: These help strengthen the core and back muscles, which help support the spine. Having strong muscles can improve posture and movement, as well as reduce pain.
- Balance training: This can help improve stability and reduce the risk of falls.
The outlook for AS is difficult to predict because it varies widely from person to person and the progression is often not constant.
Important factors for measuring outlook include levels of functional ability, spinal mobility, and joint damage.
Some people will experience severe functional loss, while others will hardly notice their symptoms.
Around 1% of people experience long-term remission, wherein symptoms cease to develop.
On the other hand, some people may have life threatening complications that affect the heart, lungs, or nervous system.
Smoking can lead to poorer outcomes.
AS is a type of arthritis that affects the spine and lower back. It is most common in males and tends to appear in late adolescence or early adulthood.
Although there is currently no cure for AS, many treatments can help slow or stop the progression of the condition. Daily management, such as an exercise program, can help people control their symptoms.