Ankylosing spondylitis is a form of chronic, progressive arthritis primarily affecting the lower spine. On this page, you will find information on how ankylosing spondylitis develops and the symptoms associated with this disease.
Also, learn how this form of arthritis is diagnosed; how symptoms can be relieved through drug treatments and physical therapy; and more information, including how to reduce your risk of ankylosing spondylitis.
Contents of this article:
What is ankylosing spondylitis?
Like an "itis," ankylosing spondylitis is an inflammatory condition, in this case affecting the spine. This particular form of chronic, progressive arthritis primarily affects the lower spine and is a systemic (whole body) inflammatory condition with symptoms ranging from stiffness and pain to severe deformity.
X-rays of the spine, especially around the hip, are used to confirm a suspected diagnosis of ankylosing spondylitis, but may not show the early condition.
Estimates vary, but more men than women are thought to be affected by ankylosing spondylitis. One estimate says three times more men,1 while another says nine times2. Unlike the wear-and-tear type of arthritis, osteoarthritis, ankylosing spondylitis usually has an onset between young adulthood and 40 years of age.1,2
The condition is around three times more common among Caucasians than African Americans,2 and runs in families - with the condition being 10 to 20 times more likely for people who have a first-degree relative (parent or sibling) with the disease.1
Ankylosing spondylitis is often abbreviated to AS and is also known as seronegative spondyloarthropathy, and simply spondylitis.2
The condition is grouped into a set of overlapping arthritis disorders that doctors call the spondyloarthritides or spondylarthritis. In addition to ankylosing spondylitis, this classification includes other types of spondylitis caused by syndromes such as inflammatory bowel disease and psoriasis.3
One estimate puts the prevalence in the US of all spondylarthritis on a par with rheumatoid arthritis.4
Around 1% of the adult population is affected by spondylarthritis, with an estimated 1.7 million Americans aged 20-69 years thought to have the condtion.4 In the UK, around 200,000 people have been specifically diagnosed with ankylosing spondylitis.5
Fast facts on ankylosing spondylitis
Here are some key points about ankylosing spondylitis. More detail and supporting information is in the body of this article.
- Ankylosing spondylitis is a type of arthritis.
- It mostly affects the lower part of the spine, and where it joins to the hip.
- An inflammatory disease, ankylosing spondylitis is characterized by pain and stiffness and can lead to loss of mobility.
- The disease process leads to erosion of bones in the spine, which can become fused, leading to spinal deformity in the advanced cases.
- Ankylosing spondylitis can be difficult to diagnose but has a particular pattern of pain symptoms, and can be seen on X-ray in progressed cases.
- There is no cure for ankylosing spondylitis, but the pain and inflammation can be managed with drugs. Physical therapy can also relieve and prevent some of the effects of AS.
What causes ankylosing spondylitis?
Doctors know a lot about how ankylosing spondylitis develops and leads to symptoms, but they are still trying to understand what causes the disease and what influences its progression.2,5-10
The symptoms of ankylosing spondylitis are caused by inflammation of parts of the lower spine. This inflammation can lead to damage and fusion - through the growth of new bone - in the spine, hips, and the joints between the two (the sacroiliac joints). Such changes can lead to a deformity known as kyphosis (curvature of the spine). Other parts of the body can also be affected.
The fusion can develop as a result of the inflammation of the tissues that connect to bones. Known as enthesitis, the inflammation in these ligaments (connecting bones to bones) and tendons (muscles to bones) can cause them to transform into bone. This process, called ossification, happens because the inflammation gradually erodes the margins of the joint, which are replaced first by fibrous cartilage and then by bone.3
It is not yet known why this chronic inflammatory process occurs in people with ankylosing spondylitis. The condition often runs in families however, and a particular gene has been linked to the condition, suggesting that there is an inherited predisposition to ankylosing spondylitis.
This gene, called human leukocyte antigen B27 (HLA-B27), acts as a genetic marker of the disease because it is found in most people who develop AS. Its link to the condition is not clear though, as most people in the population who carry this gene never develop the condition. As such, there are thought to be external (environmental) triggers for ankylosing spondylitis.
Recent development in understanding ankylosing spondylitis
Genetic research on the DNA of some 3,000 people with ankylosing spondylitis, published in Nature Genetics in 2011, confirmed the association with the HLA-B27 gene, but also revealed lots more genetic clues about the condition's causes.
Signs and symptoms of ankylosing spondylitis
Three main symptoms characterize ankylosing spondylitis:2
- Loss of mobility.
Pain is the main symptom of ankylosing spondylitis, especially in the lower back and buttock areas in the early stages of the disease.2 Read on to the next section about diagnosis to find out the typical onset and character of pain in ankylosing spondylitis, and how it differs from other causes of back pain.
Although lower back pain is a key symptom of ankylosing spondylitis, the inflammation is not confined to the lumbar spine - it is systemic - meaning that pain can also arise in other parts of the body, such as:2,5
- In other joints (arthritis and synovitis symptoms)
- In the neck (upper - cervical - spine)
- At the top of the shin bone in the lower leg
- Behind the heel of the foot (inflammation - enthesitis - in the Achilles tendon)
- Under the heel of the foot
- In the chest (which can restrict breathing).
People with ankylosing spondylitis may also experience fatigue - a feeling of being tired and having low energy most of the time.5
In about a quarter of cases, ankylosing spondylitis also affects the eyes, including the iris (the colored part of the eye) and other parts of the eye apparatus around it. This inflammation (known as iritis or uveitis, depending on the location) can cause redness and pain, but does not usually impair vision.2,5
Other systemic signs of the disease may include neurological and cardiovascular changes.1
Ankylosing spondylitis tests and diagnosis
The first step towards a diagnosis of ankylosing spondylitis is a consultation with a physician who will ask about symptoms and personal and family medical history. They will also carry out a physical examination, and arrange tests where necessary. While imaging and laboratory tests are used, there is no definitive biological test for ankylosing spondylitis.1,2,5
The condition can be difficult to diagnose, owing to the lack of a definitive test, the overlap of symptoms with other health issues, and the slow progression of the disease. There are, however, telltale features that may help to make the diagnosis, such as back pain that:5
There are telltale features that may help to make the diagnosis of ankylosing spondylitis such as lower back pain.
- Does not improve with rest
- Causes sleep disturbance.
During the initial consultation, the doctor "takes a history" - asks questions about the symptoms and their context. This can help to rule out other potential causes of the back pain by distinguishing inflammatory causes from non-inflammatory ones. If the doctor uncovers the following features of inflammatory back pain, ankylosing spondylitis may be the culprit:1,2
- Gradual onset of back pain before the age of 40 years, and not caused by a trauma (injury)
- The complaint has persisted for longer than three months
- There is spinal stiffness in the mornings, and symptoms improve with exercise and motion.
Other factors, if present in addition to the above, will heighten the suspicion of ankylosing spondylitis, including a family history of the disease; that is, a first-degree relative already having the diagnosis - a parent or sibling - diagnosed with the disease.1
The three distinguishing features listed above will only result in a diagnosis of "probable" ankylosing spondylitis. Imaging tests are needed to confirm the diagnosis, and changes may not be immediately visible on such tests, which can delay diagnosis.5
The initial consultation may also include a physical examination of the spine and pelvis, heels, and chest. The flexibility of the spine can be checked by movements in different directions. The doctor may also check chest expansion by asking the patient to breathe deeply. This is to ascertain whether breathing is restricted by curvature of the spine or inflammation in rib joints.2,9
Before referring a patient to a rheumatologist and radiologist for further investigation and imaging, the doctor may order blood tests.
While no blood tests can confirm ankylosing spondylitis, they can add weight to a likely diagnosis and rule out other causes of symptoms.1
The tests for inflammation include erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and complete blood count (CBC). If other causes such as rheumatoid arthritis are suspected, testing for rheumatoid factor (RF) and antinuclear antibodies (ANA) can help to rule out these conditions.1
Testing for a genetic marker of AS (a blood test for HLA-B27, mentioned above) is not usually helpful to the process of diagnosis because not everyone with the gene develops the condition, and some people with the condition do not have the gene.1,5 Such tests may, however, help inform future research into AS development, progression and treatments.
X-rays can reveal changes to the lower spine and pelvis, showing both early and more advanced signs of ankylosing spondylitis.
However, ankylosing spondylitis may not produce any changes visible on X-ray for several years in the early stages of the disease. Some of the earliest signs are usually seen as erosion around the sacroiliac joint (where the spine joins the pelvis).1,2,5
Later signs visible on X-ray can take around 10 years to develop and include the abnormal formation of bone between the spinal vertebrae (known as fusion). Such advanced cases of ankylosing spondylitis can also show calcium deposits in ligaments and spinal discs, and old spinal fractures.1,2
These later changes lead to the appearance of a "bamboo spine" on X-ray images, where squaring off gives a symmetrical and segmented appearance.1,2
MRI and ultrasound scanning may also be used to investigate ankylosing spondylitis, but while they can reveal earlier signs of the condition, they are not a routine part of testing.1
Images taken by MRI and ultrasound are sensitive enough to reveal inflammatory changes in ligaments and tendons.5
Taken alongside imaging tests, a physical examination is included in the "modified New York criteria" followed by doctors for a definitive diagnosis of ankylosing spondylitis.1
Remember, though, that definitive diagnosis is not always possible, because early stage AS may not cause signs that can be seen on scans.
For a diagnosis of AS, the New York criteria specify that one of the following must be present in addition to positive scans:1
- A positive history for inflammatory back pain (as diagnosed against the three criteria above), or
- Restriction of motion of the abdominal (lumbar) spine - both in the to-and-fro and the side-to-side directions, or
- Restricted chest expansion (after taking account of age).
Recent developments in tests and diagnosis for ankylosing spondylitis from MNT news
In the Proceedings of the National Academy of Sciences, researchers from the University of Southampton in the UK describe how they found the enzyme ERAP1 is highly variable in humans, and specific combinations of variants are found in people with ankylosing spondylitis.
Treatment and prevention of ankylosing spondylitis
Ankylosing spondylitis cannot be prevented or cured, and the damage caused by it cannot be reversed, but there are a number of options available to help relieve symptoms and manage progression. These options include physical therapies and advice, drugs, and, in rare cases, surgery.1,2,5,7,9,11-12
The most important step to take for people with ankylosing spondylitis is to seek help from doctors, including rheumatologists. This can require a number of clinic visits, and can be frustrating because the slow development of the condition means that a definitive diagnosis is hard to come by in the earlier stages of AS. However, proper medical care enables better monitoring and treatment programs.
The following two main approaches are typically used in the management of ankylosing spondylitis:1,5
- Painkillers and other drugs to reduce pain and inflammation
- Physical therapy and exercises to maintain movement and posture.
Surgery is used only rarely, in severe cases to correct great deformity - for example, when the spine is bent over too far - or to replace a joint, such as in hip replacement.5
The main drug group used to ease the pain symptoms and inflammation of ankylosing spondylitis are the nonsteroidal anti-inflammatory drugs (NSAIDs) - such as ibuprofen, naproxen and diclofenac. (Acetaminophen and codeine are also options if NSAIDs are unsuitable or insufficient.)1,5,9
Unfortunately, some NSAIDs compromise bone health by reducing the creation of new bone (this is why spinal fusion patients are usually told not to take NSAIDs immediately after surgery).
Other drug options are available, and it is important to discuss options with a qualified doctor to determine whether or not the following medications may be beneficial:1,5,9
- Locally injected corticosteroids
- Disease-modifying anti-rheumatic drugs (DMARDs) - such as sulfasalazine (US brand names: Azulfidine or Sulfazine) and methotrexate (Otrexup, Rheumatrex, or Trexall)
- Tumor necrosis factor (TNF) antagonists - adalimumab (Humira), certolizumab (Cimzia), etanercept (Enbrel), golimumab (Simponi), or infliximab (Remicade).
Physical therapy for ankylosing spondylitis can help to prevent symptoms and is tailored to individuals' needs.5 In general, physical therapists will devise a program including exercises directed at the joints or that promote extension and mobility of the spine.13
The physical therapist will design a program that can help patients maintain good posture and motion in the joints. Daily exercises and special training and therapeutic exercises are designed to help strengthen certain muscle groups, with the intention of strengthening muscles that oppose, or work in the opposite direction to, the potential deformities of ankylosing spondylitis.1
Physical therapy exercises are referred to as strengthening exercises and range-of-motion exercises, and there are many ways to do them, including while in water (for added support).9
One example of a strengthening measure is to perhaps read a book while your body is facing down, and your back is extended - by resting on your elbows or some pillows. This posture works the muscles that act in opposition to the abnormal curvature of the spine in AS.
In addition to receiving care from doctors, rheumatologists and physical therapists or rehabilitation specialists, other doctors may be involved with the care of a patient with AS. This is because of the systemic nature of ankylosing spondylitis, which may require attention from an:9
- Ophthalmologist (for eye disease)
- Gastroenterologist (for bowel disease)
- Physiatrist (a medical doctor specializing in physical medicine and rehabilitation - not to be confused with psychiatrist).
Recent developments in the treatment of ankylosing spondylitis
This study was randomized and included 60 people with AS. The researchers presenting the data said exercises involving an inflatable ball improved function, muscle strength, and mobility.