Fact: In the United States, a disease is rare if it affects fewer than 200,000 people. Ankylosing spondylitis is part of a class of diseases called spondyloarthritis, which affects an estimated 2.7 million American adults, making it more common than multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS) and rheumatoid arthritis (RA) combined. The exact number of people with ankylosing spondylitis in the Unites States remains unknown.

Fact: The cause of ankylosing spondylitis remains unknown. The disease can affect multiple people in the same family but is likely caused by a mix of multiple genetic and environmental factors that have yet to be fully identified. Genetic markers that have been identified include HLA-B27, ERAP1, IL1A, IL23R, the presence of which can increase the likelihood of being diagnosed. It remains unclear how and to what extent these genes contribute to the chance of developing ankylosing spondylitis.

Fact: Testing for HLA-B27 can help confirm a suspected ankylosing spondylitis diagnosis, but is not a reliable predictor. The HLA-B27 gene, a variation of the human leukocyte antigen-B complex, is present in about 90 percent of people who have ankylosing spondylitis; 10 percent of those with the disease do not have the gene. Additionally, HLA-B27 occurs in over six percent of the general population, the majority of whom will never develop ankylosing spondylitis.

There is no single diagnostic test for ankylosing spondylitis, which is generally diagnosed after reviewing a combination of variables not limited to: imaging, inflammation levels in the blood, genetic markers, family history, and symptoms. The hallmark feature of ankylosing spondylitis is inflammation in the sacroiliac joints. Importantly, ankylosing spondylitis presents differently in every person, making it difficult to rely on a rigid set of diagnostic criteria.

Fact: Ankylosing spondylitis affects all genders but exact ratios are unknown; currently more men are understood to be diagnosed, but the ratio is declining as women are being diagnosed at a faster rate. Women can experience a longer delay in being diagnosed because symptoms can be different than those traditionally associated with the disease. Patient communities report that some physicians still believe women cannot get ankylosing spondylitis.

Fact: Ankylosing spondylitis is characterized by inflammation in the sacroiliac joints and often the joints of the spine. As the disease progresses bone spurs can form and in severe cases complete spinal fusion can occur and force the spine into a hunched, rigid position called kyphosis. Treatments for ankylosing spondylitis are meant to slow down progression of the disease and reduce the chance of bone spur formation and fusion.

Fact: Ankylosing spondylitis is a systemic, or whole body, inflammatory disease that can affect multiple parts of the body including joints and organs. The disease primarily affects the spine and specifically the sacroiliac joints, but it can also cause inflammation and pain in peripheral joints and cause damage to the eyes, heart, lungs, kidneys, and other organs. In addition, the disease can cause significant fatigue and affect sleep and cognitive function.

Fact: While symptoms vary in different populations, reports vary on whether men or women overall experience ankylosing spondylitis with greater severity. Symptoms do present somewhat differently by gender; women generally experience more peripheral, or outer joint, symptoms whereas men generally show more axial, or spinal, activity. Additionally, studies have shown that black people experience the disease more severely than other ethnic groups.

Fact: There is no cure, and while temporary disease inactivity is possible, researchers have not defined what medical remission looks like. Diet has not been scientifically shown to slow progression of the disease but can relieve symptoms. Treatment recommendations for ankylosing spondylitis include nonsteroidal anti-inflammatory drugs (NSAIDs), tumor necrosis factor inhibitors (TNFi), and physical therapy or exercise. Other treatments may be conditionally recommended to manage symptoms.

Fact: Ankylosing spondylitis is officially classified as an immune-mediated inflammatory disease. While it has both autoimmune and auto-inflammatory characteristics, researchers have not proven the disease fits in either category.

Fact: More than 100 forms of arthritis exist, including ankylosing spondylitis and rheumatoid arthritis. Both are inflammatory and systemic, but ankylosing spondylitis is part of a disease group called spondyloarthritis, while rheumatoid arthritis is a separate disease under the arthritis umbrella. Ankylosing spondylitis is characterized by enthesitis, or inflammation where ligaments and tendons attach to bone; rheumatoid arthritis is characterized by synovitis, or inflammation inside the joints.

Fact: Ankylosing spondylitis affects every person differently including disease severity; the types, location and number of symptoms; the age of onset and length of time to diagnosis; the timeline of progression and inactivity; reaction to treatments; and presence or lack of imaging or other evidence of disease activity.

Ankylosing spondylitis is a complex, common disease that affects millions of people. Despite its prevalence, inaccurate information is easy to find. Keep looking for the facts!