What Is Ankylosing Spondylitis? Key Facts You Should Know

Ankylosing spondylitis is a chronic inflammatory disorder that mainly affects the spine.

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Lower back pain is not necessarily a rare phenomenon: 80 percent of U.S. adults suffer from low back pain at some point in their lives, according to the National Institute of Neurological Disorders and Stroke. But for many of those Americans, the pain can be alleviated by getting a new mattress, or fixing their lifting form.

This is not the case for people with ankylosing spondylitis, or AS. “Ankylosing spondylitis is a chronic inflammatory disorder that mainly affects the spine,” says Jessica Patel, MD, a rheumatologist at Mount Sinai Hospital in New York City. “It affects the flexibility and mobility of the back and other joints as well.” In fact, ankylosis and spondylitis come from the Greek words for “crooked” and “vertebra,” respectively.

Ankylosing spondylitis is a type of arthritis, and is the most common condition within the spondyloarthritis family, according to the American College of Rheumatology. Spondyloarthritis also includes axial spondyloarthritis (which creates lower back pain) and peripheral spondyloarthritis (which causes pain and swelling in joints other than the spine, such as the hands, elbows, shoulders, knees, and feet). It’s possible to be diagnosed with multiple types of spondyloarthritis.

Symptoms of Ankylosing Spondylitis

“Ankylosing spondylitis primarily affects large joints in the body, particularly where there are a lot of ligament attachments to bone,” says Themistocles Protopsaltis, MD, spine surgeon at NYU Langone Hospital.

A key feature of AS is the inflammation of the sacroiliac joints, which is where the spine meets the pelvic bone. “There are really strong ligaments here [in the sacroiliac joints],” says Dr. Protopsaltis. “Those ligaments and those attachments to those ligaments can become inflamed as the immune system attacks the attachment.”

The inflammation can make these joints painful and stiff. Over time, the vertebrae may fuse together (which is known as ankylosis) and make the spine inflexible, according to the Arthritis Foundation (AF). “At the very end of the disease, you can have very little joint pain, but now you have a joint that doesn’t move anymore,” says Dr. Protopsaltis.

The inflammation and pain may spread to the hips, shoulders, chest, neck, and even the organs, especially the eyes and bowels. Around 26 percent of people with AS also suffer from inflammatory bowel disease and as much as 40 percent also have uveitis (an eye disease), according to a 2014 article in Hip & Pelvis journal.

Possible Causes of Ankylosing Spondylitis

The cause of AS inflammation is unknown, but researchers have some theories. “Ankylosing spondylitis is an autoimmune disease,” says Dr. Protopsaltis. “It’s theorized to be something that occurs after an infection, where the body might attack an infecting organism. It then recognizes different parts of the joints as similar to that infecting organism and attacks those joint surfaces.”

Doctors also know that genetics play a role in the development of this arthritis. Most people with AS have a gene known as HLA-B27.

The role of HLA-B27 in the development of AS is pretty clear: This gene is found in 90 percent of caucasians with AS, but only 8 percent of caucasians without AS, according to AF. That said, you can get AS without having this gene, and having the HLA-B27 doesn’t guarantee you’ll develop AS: Only 1 in 20 people with the gene get AS, according to the National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS).

Additionally, researchers have identified two more genes—IL23R and ERAP1—that may increase the risk of developing AS, according to NIAMS.

Just short of half a million Americans live with AS, and it affects more men than women. “Ankylosing spondylitis often affects people at a younger age,” says Dr. Patel. Symptoms usually begin in the late teens or early 20s, or at least before age 45. Learn more about risk factors for AS here.

Treatment for Ankylosing Spondylitis

AS has no cure, but medications can help manage symptoms and prevent the progression of the disease. Lifestyle changes can help reduce inflammation and lessen symptoms. Eating a healthy and anti-inflammatory diet, not smoking, and exercising are recommended. In rare cases, doctors may use surgery to straighten the spine.

Learn more about treatment for ankylosing spondylitis here.

“If you have back pain and you’re concerned about it being an inflammatory arthritis or ankylosing spondylitis, I would talk to your doctor and they will give you a referral to a rheumatologist,” says Dr. Patel.