From surprising symptoms to misdiagnoses to the toll on quality of life, AS is complex, complicated disease, for patients and their loved ones.
Ankylosing spondylitis (AS) and its related conditions, called spondyloathropathies, affect millions of Americans, but these diseases aren’t exactly a household name. Ankylosing spondylitis is a type of inflammatory arthritis that predominantly affects the spine and sacroiliac joints (where the spine connects to the pelvis), causing lower back, hip, and pelvic pain. But AS is a complex, mysterious disease that can affect many other different parts of the body too.
Chances are you might know someone with AS, or are concerned about potential signs and symptoms of AS. Here are important facts about AS you need to know to help you better understand the disease and treatment.
1. Ankylosing spondylitis is an inflammatory disease
Unlike osteoarthritis, AS isn’t a result of the joints’ natural wear and tear, but develops because of chronic inflammation in the body. Because of the nature of inflammatory pain, the symptoms will also be different from wear-and-tear arthritis, says Santa Fe rheumatologist Hillary Norton, MD, who has AS herself. “Something that differentiates inflammatory pain is that it tends to get worse when you’re not moving the joints,” she says. Because you don’t move around when you’re in bed sleeping, that also means that it tends to get worse at night and in the morning. Here are other key differences between mechanical and inflammatory back pain.
2. AS is a type of spondyloarthritis
Ankylosing spondylitis falls under the umbrella term of “spondyloarthritis” or “spondyloarthropathies,” which is a group of types of inflammatory arthritis that affect the spine. AS is the prototypical disease, while related types of spondyloarthritis include psoriatic arthritis, reactive arthritis (associated with an infection), and enteropathic arthritis (associated with inflammatory bowel disease). “There’s no strict line to differentiate one from the other,” says Bharat Kumar, MD, associate rheumatology fellowship program director in the division of immunology at the University of Iowa Hospitals and Clinics, “but ankylosing spondylitis has a certain set of signs and symptoms that make it more likely to be ankylosing spondylitis than other causes of inflammatory back pain.”
3. Back pain in AS has some unique traits
For one thing, AS back pain gets worse when you sit still or rest, particularly when you sleep, and particularly in the second half of the night. Patients commonly report getting out of bed in the second half of the night in pain. AS also causes something people refer to as “alternating buttock pain,” which stems from the lower back into the rear, often striking one side at a time.
4. AS symptoms vary from person to person
With so much overlap between ankylosing spondylitis and other spondyloarthropathies, there’s a wide-ranging checklist of symptoms that doctors look for when diagnosing AS. A classic case would start from the bottom of the back, where the spine meets the pelvis, and work its way up, but not everyone will present that way. Women in particular are more likely to see the pain start from higher up on the back, near the bra line, says Dr. Norton. Other people with AS might have peripheral spondyloarthritis, which means that the inflammation spreads to joints beyond the spine, such as the knees and hips.
While chronic lower back pain that gets better with movement and worsens with rest and that starts at a younger age (before age 45) is trademark symptom of AS, people are diagnosed with AS without having back pain as their main complaint.
5. AS symptoms aren’t limited to the joints
“Ankylosing spondylitis is a systemic inflammatory condition,” says Dr. Kumar. “We see it more in the joints because it causes the most pain in people, but AS can affect all kinds of other organs.” As a type of spondyloarthritis, AS also can be associated with symptoms related to other diseases under the umbrella, such as psoriasis and IBD. AS is linked with to red, irritated, painful eyes, a condition known as uveitis. In more severe, less controlled cases, the inflammation from AS can even increase the risk of heart problems.
6. Fatigue is a major AS symptom
Fatigue — full-body exhaustion that goes beyond just feeling tired from not enough sleep — is a common complaint in many different kinds of chronic illness. AS is no exception. One study found that about 65 percent of AS patients report fatigue as a symptom.
7. AS strikes the young
Although we tend to associate arthritis with middle age, inflammatory arthritis tends to first occur at younger ages. And of those, AS hits particularly young — about 80 percent of patients will experience their first symptoms before age 30; a mere 5 percent will notice the signs at 45 or older, according to Johns Hopkins Arthritis Center.
8. AS can affect men and women differently
Men are more likely than women to develop AS, though doctors aren’t sure why. There also seem to be sex differences in how the disease affects male vs. female patients. A 2018 research review found that men tend to have more and faster radiographic damage, while women are more likely to have more non-joint symptoms like psoriasis and IBD, and higher disease activity. Read more about differences in how AS affects women and men.
9. Genes can play a role in AS
Even though scientists haven’t figured out why certain people develop ankylosing spondylitis, genes play a role. In particular, the genetic variant HLA-B27 is associated with an increased risk of developing AS, and other genes have recently been linked with the disease (such as ERAP1, IL23R, and EL1A). That said, testing for the HLA-B27 gene can’t rule out or clinch a diagnosis. Only about 2 percent of people who carry the HLA-B27 gene will go on to develop spondyloarthritis, according to the Spondylitis Association of America, and not everyone with AS has the HLA-B27 gene.