What is Ankylosing Spondylitis?
Ankylosing spondylitis is a specific type of arthritis driven by chronic inflammation, which principally assaults the joints of the spine. The disease process most often begins in the sacroiliac joints, the crucial connection point between the base of the spine and the pelvis. A key characteristic of this condition is enthesitis, which is inflammation occurring precisely where ligaments and tendons attach to bone. Over an extended period, this persistent inflammation can damage the affected joints. In response, the body initiates a healing process that can go awry, leading to the gradual formation of new bone. This new bone growth may eventually bridge the gap between vertebrae, effectively fusing them together into a single, rigid unit—a process called ankylosis. While the spine is the main area affected, the inflammation can also impact other parts of the body, including the hips, shoulders, ribs, and even the eyes.
Causes:- A Misdirected Immune Response: The fundamental problem in ankylosing spondylitis is an error in the immune system. Instead of solely targeting foreign invaders like viruses, the body’s defense mechanisms mistakenly identify the entheses—the specific points where ligaments and tendons anchor to bone, particularly in the spine—as a threat and launch a sustained inflammatory attack against them.
- A Strong Genetic Link: A specific genetic marker, known as Human Leukocyte Antigen B27 (HLA-B27), is present in a vast majority of individuals with the condition. While possessing this gene does not guarantee the disease will develop, it profoundly increases an individual’s susceptibility by influencing how the immune system operates and recognizes self from non-self.
- Potential Environmental Triggers: Researchers theorize that in genetically susceptible individuals, an encounter with an external agent may initiate the disease process. It is suspected that a prior bacterial infection, particularly in the gastrointestinal tract, could act as the initial catalyst that sets off the misguided immune response that characterizes the disease.
- Genetic Makeup: The presence of the HLA-B27 gene is the single most important known risk factor. Although many people with this gene never develop the condition, its presence, particularly in combination with a family history of the disease, vastly increases an individual's susceptibility.
- Age at Initial Onset: Unlike many degenerative forms of arthritis associated with aging, ankylosing spondylitis typically makes its first appearance earlier in life. The onset of symptoms most frequently occurs in late adolescence and early adulthood, generally between the ages of 20 and 40.
- Biological Sex: A notable disparity exists in the prevalence of the disease between the sexes. Men are diagnosed with ankylosing spondylitis more often than women and may also have a greater tendency to experience the more severe structural fusions in the spine.
