Ankylosing spondylitis (AS) is a rare type of arthritis that causes pain and stiffness in mainly the spine. AS can also affect other areas of the body such as the shoulders, hips, ribs, heels, and small joints of the hands and feet. The soft tissues, joints, tendons, and ligaments are the main sites of inflammation seen in AS. The main symptom of AS is inflammatory spinal pain; with time, some patients develop fibrosis and calcification, resulting in the loss of flexibility and the fusion of the spine.
As an autoimmune disease, AS develops through complex interactions between genetic background and environmental factors. Most individuals who have AS also have a gene that produces a genetic marker, a protein called HLA-B27. This marker is found in more than 95 percent of people in the Caucasian population with AS. It is important to note, however, that one does not have to be HLA-B27 positive to have AS. Also, a majority of people with this marker never develop AS.
Scientists suspect that other genes, along with a triggering environmental factor such as a bacterial infection, for example, are needed to activate AS in susceptible people. The differences observed in immune cells and cytokines in AS suggest the role of immunological effects in AS pathogenesis.3 HLA-B27 transgenic rats failed to develop features of AS in a germ-free environment, which changed when commensal bacteria were introduced into the germ-free models, suggesting possible interactions between HLA-B27 and the microbiome. One classic hypothesis has been that AS may start when the defenses of the intestines break down and certain bacteria pass into the bloodstream, triggering changes in the immune response.
The coexistence of AS and intestinal inflammation has been known for some time. Around 70% of patients with AS develop subclinical gut inflammation. This altered composition of microorganisms in the gut leads to more bacteria that play a role in inflammation and AS progression. A study done on patients with AS found an increase in the abundance of Lachnospiraceae, Ruminococcaceae, and Prevotellaceae.5 Altered gut bacteria produce high levels of inflammatory cytokines that when enter into the bloodstream can travel to distant sites and attack the soft tissue of the body leading to the progression of AS.
The severity of AS varies greatly from person to person, and not everyone will experience the most serious complications or have spinal fusion. Some may experience only intermittent back pain and discomfort, while others may experience severe pain and stiffness over multiple areas of the body for long periods of time. AS can be debilitating and, in some cases, lead to disability.
Almost all cases of AS are characterized by acute, painful flare ups which are followed by temporary periods of remission when symptoms subside. The hallmark feature of ankylosing spondylitis is the involvement of the sacroiliac (SI) joints during the progression of the disease. The SI joints are located at the base of the spine, where the spine joins the pelvis. The pain typically becomes persistent (chronic) and is felt on both sides, usually lasting for at least three months. Over the course of months or years, the stiffness and pain can spread up the spine and into the neck. Pain and tenderness spreading to the ribs, shoulder blades, hips, thighs, and heels is possible as well.