Ankylosing spondylitis is a type of arthritis that typically begins in the spine and the joints between the spine and the pelvis. It causes pain, stiffness, and may affect the shape of the spine and mobility.

Symptoms can spread to other parts of the body and, eventually, this chronic inflammatory disease can cause some of the bones in the spine to fuse together.

The early diagnosis and treatment of ankylosing spondylitis (AS) can reduce the risk of spinal deformity and help people manage the symptoms.

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Pain and stiffness in the lower back, hips, and buttocks may be an early sign of AS.

The Spondylitis Association of America notes that symptoms of AS vary greatly between individuals, as does the age at which it develops.

The Association also states that AS may present differently in a minority of people, particularly women, with the pain beginning in areas other than the lower back.

For example, AS may start in the neck, ankle, elbow, or another joint.

Around 1 in 10 people with the condition experience symptoms so severe, they are at risk of long-term disability.

Early signs and symptoms

Some of the more common early signs and symptoms of the condition include:

  • pain in the lower back, hips, and buttocks
  • stiffness in the lower back, hips, and buttocks
  • neck pain
  • ligament and tendon pain
  • tiredness
  • night sweats
  • mild fever
  • appetite loss
  • general discomfort

These symptoms may:

  • develop gradually over several weeks or months
  • be more prominent in the morning or during the night
  • be worse after periods of inactivity
  • improve after light exercise or a warm shower
  • appear or intensify at irregular intervals
  • be felt on one or both sides of the body

Signs and symptoms over time

Over time, the symptoms become chronic. At this stage, signs and symptoms include pain, stiffness, and tenderness on both sides of the body. These symptoms often spread to other body parts.

AS can eventually lead to changes in posture, and some people with AS may look like they are stooped forward, which is known as kyphosis.

Tiredness, caused by the body’s reaction to inflammation, is another common long-term symptom.

Areas most commonly affected

AS symptoms tend to affect several areas of the body, including:

  • the spine
  • neck
  • ribs
  • shoulder joints
  • hips
  • thighs
  • joints of the hands
  • joints of the feet

AS can, however, potentially affect any joint.

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Breathing difficulties due to a reduced lung capacity may be a complication of AS.

People with severe cases of AS and advanced inflammation may experience the formation of new bone. As the body attempts to heal itself, sections of the spinal bones fuse together, causing stiffness and loss of flexibility.

Other complications include:

  • Anemia of inflammation and chronic disease. This type of mild to moderate anemia commonly occurs in people who have a chronic illness. It is the second most common type of anemia and can contribute to tiredness in those with AS.
  • Bowel inflammation. Some people with AS have inflammatory bowel disorders (IBD), such as Crohn’s disease or ulcerative colitis. Some research suggests that up to 10 percent of people with AS develop IBD, and vice versa.
  • Eye inflammation. Around 33 percent of people who have AS will experience at least one case of eye inflammation. Pain, blurred vision, sensitivity to light, and watering are symptoms of this complication.
  • Heart inflammation. Inflammation of the aorta, the body’s largest artery, can occur in those with AS. The aorta carries blood from the heart to the other areas of the body. When the aorta becomes inflamed, it is unable to perform this role so well.
  • Reduced lung capacity. Fusion of the bones may lead to a stiffening of the rib cage, which might cause breathing difficulties.
  • Spinal compression fracture. Weakened bones can eventually collapse in those with AS, an occurrence known as a spinal compression fracture. A spinal compression fracture can lead to poor posture and may injure the spinal cord and nerves.

Diagnosis is often carried out by a rheumatologist who specializes in diseases of the joints, muscles, and bones.

AS may be diagnosed through a physical exam, blood tests, and imaging tests.

Physical exam

The doctor will check pain responses in different areas of the body, as well as the range of motion of the spine. They may also check to see how far the chest expands and how easy it is to breathe.

The doctor will also take a full medical history and family history of illness.

Blood tests

Doctors may also request blood tests to detect the presence of the HLA-B27 gene. This gene is present in up to 95 percent of white people in central Europe and North America who have AS.

However, not everyone with the gene goes on to develop AS. Only 1 to 2 percent of people with the HLA-B27 gene are affected by the condition.

Blood tests can also indicate the presence of inflammation, which may help to inform diagnosis.

Imaging tests

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An X-ray or MRI scan may be used by a doctor if the back pain has lasted for 3 months or more.

X-rays may be performed on the spine to see if the joints are damaged or fused. Doctors may order an MRI scan if nothing shows up on the X-ray. MRI’s can detect inflammation without joint damage.

AS is a chronic disease, so some doctors may wait for a clear pattern of symptoms to emerge. A history of back pain lasting for 3 months or more is often a key factor in diagnosis.

When to see a doctor

If a person experiences pain in the lower back, hips, or buttocks, it is important to see a doctor. This is particularly important if this pain is more severe upon waking, or it persists over time.

People should also seek medical advice if they experience any of the other symptoms or complications of AS.

The cause of AS is unknown. People with the HLA-B27 gene are at greater risk of developing the condition, although not everyone with the gene develops AS. Equally, not everyone with AS carries the gene.

Also, some research has identified other risk factors in particular groups of people.

Risk factors for the development of AS include:

  • age
  • sex
  • genetics and family history

The American Academy of Family Physicians advise that AS is most common in white men who are aged 15 to 40. Approximately three times more men than women develop AS with signs and symptoms usually appearing in early adulthood. However, it also affects women, and people of all ages and races.

Estimates from European populations indicate that AS affects between 2 and 5 adults in every 1,000. In some groups, however, AS may affect as many as 1 in every 100 people.


As the cause of AS is not known, it is not possible to prevent its onset. However, early diagnosis can prevent or limit disease progression and help manage symptoms.