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Ankylosing Spondylitis: Definition, Causes, Risk factors & Complications

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Ankylosing Spondylitis

What is Ankylosing Spondylitis?

Ankylosing Spondylitis is a type of arthritis which causes recurring inflammation of the spinal bones and other joints such as sacroiliac joints. It is a chronic disorder which is also known as Marie-Strümpell disease or Bechterew's syndrome. The symptoms of this condition include pain and stiffness from the neck down to the lower back. Chronic inflammation of these leads to ankylosis (new bone formation in the spine) and spinal bones fuse together completely, resulting in a condition known as "bamboo spine", in which the spinal column becomes completely rigid. The changes can vary from mild to severe and may cause significant deformities. For doctors, it is already not clear enough what causes Ankylosing Spondylitis.

Ankylosing Spondylitis is a systemic disease, which means that the symptoms of this condition are not just limited to the joints, It can also affect other areas of the body, such as the shoulders, ribs, pelvic bones, heels, and small joints of the upper and lower extremities. It can also affect eyes and cause inflammation (redness and pain) of the eyes, and rarely, heart and lung problems may also develop. People with the condition can also suffer from fever, fatigue, and loss of appetite.

What Causes Ankylosing Spondylitis?

There is no known reason as to what causes Ankylosing Spondylitis, but there is a lot of information available about what effects it has on the body, and why it causes the vertebrae to become stiff and rigid.

People who have the particular HLA-B27 gene have a significantly greater risk of developing AS, but there are many people who have this gene that never develop AS. Infectious agents may be involved in the development of the disease.

Ankylosing Spondylitis: Classification

There are four different types of Ankylosing Spondylitis:

  • Slowly progressive
  • Slowly progressive with periods of exacerbations
  • Quick progressive
  • Septic

Ankylosing Spondylitis: Prevalence and Risk Factors

Ankylosing Spondylitis is more prevalent in Northern European countries and Afro-Caribbean populations. The overall prevalence of this disease is < 0.3% of the general population. Ankylosing Spondylitis is diagnosed twice as often in males as in females, but many doctors believe the number of females with the disease is underestimated because females tend to have milder symptoms. Typically, signs and symptoms of Ankylosing Spondylitis usually first appear between the ages of 15 and 25.

Ankylosing Spondylitis affects the 0.1%- 0.5% of the population. This condition usually begins in early adulthood. It can also affect children and this is known as Juvenile Ankylosing Spondylitis. It is most likely to affect males more often than females. In women, it affects the joints away from the spine. This condition is more common in some Native American tribes. Currently, there is no treatment for Ankylosing Spondylitis, but early diagnosis and treatment of this condition help control pain and stiffness and also help to prevent or reduce significant deformity.

The exact causes of AS are unknown. This condition may develop due to the combination of genetic and environmental factors. Following are the few risk factors:

  1. Sex:  Men are more likely to develop Ankylosing Spondylitis than women.
  2. Age: Ankylosing Spondylitis usually begins in early adulthood. It can also affect children.
  3. Heredity: Genetics plays an important role in disease. Most of the people who suffer from Ankylosing Spondylitis have a specific type of gene that produces genetic marker known as known as the HLA-B27. However, there are also many people who never develop AS despite having HLA-B27 gene.
  4. Frequent gastrointestinal infections: Ankylosing Spondylitis is also associated with inflammatory bowel diseases.

Ankylosing Spondylitis: Pathological Changes and Complications

Ankylosing Spondylitis causes changes to occur in your body because of the inflammation it causes in the areas where skeletal bones are attached to tendons, ligaments, discs or joints. It typically affects the sacroiliac joints, where the lower back meets the pelvis, and begins with inflammation in this area (sacroiliitis).

In the spinal column, AS starts in the fibrous tissues of the discs between the vertebrae. Ankylosing Spondylitis causes inflammation that leads to the breakdown of the tissues and, over time, makes them thickened and rigid. This leads to stiffness of the spine, and pain due to compression of the nerve roots.

Eventually, the prolonged and recurrent inflammation of Ankylosing Spondylitis can result in a complete fusion, or cementing the bones of the spine together (vertebrae). This fusion is called Ankylosis. When the spine is fused, it loses its mobility.

Because it is a systemic inflammatory disease, Ankylosing Spondylitis can affect other areas of the body away from the spine, such as the kidneys, heart, lungs, and eyes. 

Ankylosing Spondylitis complications varies greatly in everyone. Painful and debilitating as it is as it progresses. If the inflammation is left unchecked can contribute to other complications such as the following:

  • Hunched posture – a curled forward, chin to chin stance can occur if the spine fuses together in a hunched forward thereby reducing spinal flexibility. Heart, Lungs and other surrounding organs may be affected. 
  • Uveitis –is a common and frequent complication of ankylosing spondylitis, uveitis can cause rapid-onset eye pain, photophobia, and blurred vision.
  • Osteoporosis/ Osteopenia  – bones may lose mineral density resulting to brittleness and more prone to fracture.
  • Caudaequina syndrome – this rare condition involves extreme pressure and swelling of the nerves at the end of the spinal cord. The condition can cause weakness, tingling, or numbness in the legs, and/or feet on one or both sides of the body. It also causes bowel of bladder dysfunction. This condition is considered a medical emergency.
  • Spondylodisctis – is when one or more intervertebral disc or disc spaces become infected by bacteria such as Staphylococcus aureus (common), Streptococcus viridans, Mycobacterium and Brucella.  About 8% of persons with ankylosing spondylitis have this condition.


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