The Spondyloarthritis Family

These diseases all affect the spine or pelvic joints, but they have many other differences and can be difficult to diagnose.

By Linda Rath | April 11, 2022

Spondyloarthritis (SpA) is a family of inflammatory rheumatic diseases that have some key features in common, including:

  • Inflammation, pain and stiffness in the spine and pelvic joints
  • Enthesitis — inflammation where a ligament or tendon attaches to bone. If you’ve ever been sidelined by Achilles tendonitis, you know what enthesitis is.
  • A gene called HLA-B27. Having the gene doesn’t mean you’ll develop any of the conditions in the SpA family. The gene alone doesn’t cause disease, and about 98% of people who carry it never have back pain. On the flip side, people of African descent are much less likely than others to carry HLA-B27 but can still develop SpA.

All in the Family

The most common type of SpA is axial spondyloarthritis (axSpA), a term that covers both ankylosing spondylitis (AS) and nonradiographic axial spondyloarthritis (nr-axSpA). The names are confusing, but what’s important is that both mainly cause inflammation in joints in the spine and pelvis.

AS is also called radiographic axSpA or r-axSpA because it causes bone damage that’s visible on X-rays. It’s traditionally been considered a severe form of axSpA; the structural damage it causes can limit spine mobility in some people. Nonradiographic axSpA, where joint damage isn’t visible on X-rays, has long been defined as an early stage of AS. 

Those definitions have shifted in the past few years. Now, AS and nr-axSpA are seen as two regions on a spectrum of inflammatory conditions rather than early and late stages of a single disease. Many people with nr-axSpA never go on to develop AS, and some patients with AS have only mild symptoms. There are many gradations in between that vary considerably from person to person.  

Some people with SpA have arthritis outside the spine, especially in the big joints in their arms or legs (called peripheral arthritis). Though people with AS and nr-axSpA can have peripheral arthritis, too, their primary symptoms are in the spine and sacroiliac joints, where the spine link to the pelvis.

The SpA family also includes:

  • Psoriatic arthritis (PsA). Up 70% of people with PsA have both peripheral and spinal inflammation, but people with a type known as axial PsA only have arthritis in the spine.
  • Reactive arthritis. This is mainly triggered by an intestinal, urinary or genital tract infection, which is often treated with antibiotics. Arthritis usually goes away on its own.  
  • Enteropathic arthritis is related to inflammatory bowel diseases like ulcerative colitis and Crohn’s disease. Like AS, it often affects the spine but rarely causes joint destruction or disability.

What Are the Symptoms?

The main symptom of AS and nr-axSpA is low back pain. A boatload of things can cause back pain, from injuries and excess weight to depression and smoking. For many people and doctors, arthritis is low on the list. That’s one reason SpA can take years to diagnose. Another is that it may be a decade or more before bone damage shows up on X-rays. To help distinguish SpA-related pain from other causes, watch for:

  • Pain and stiffness that start gradually and last at least three months.
  • Pain that feels better when you move around, exercise and stretch, and worse when you rest; with a back injury, it’s usually the opposite.
  • Morning stiffness that makes it hard to get out of bed but improves as the day goes on.

Conditions that fall under the SpA umbrella are surprisingly varied and symptoms can overlap. In addition to back pain, you could have:

  • Psoriasis, a skin disease marked by patches of itchy red skin.
  •  Eye inflammation called uveitis, which affects about 30% to 40% of people with SpA.
  • Inflammation in your GI tract that can cause abdominal pain, unintended weight loss, and severe diarrhea.

Who Gets SpA?

Many conditions in this family, especially AS and nr-axSpA, strike young adults, often when they’re still in school or just starting careers and families. Although it was long believed that men with AS outnumbered women by three to one, it’s now known that women are underdiagnosed, especially when bone damage doesn’t show up on X-rays. Newer research suggests SpA is an equal opportunity offender, striking men and women equally. Black Americans are less likely to have AS than whites but tend to have more severe disease.  

What Causes It?

Why certain people develop SpA is still something of a mystery. Anywhere from 80% to 95% of those who have axSpA carry the HLA-B27 gene, but most people with the gene never get arthritis. Although HLA-B27 may make you more susceptible to axSpA and related diseases, it needs a trigger to set it off. Several possible triggers are being investigated, including mechanical stress on the back, though no clear link has been found so far. It’s also possible that the inciting factor is dysbiosis — an imbalance of the natural microbes in the gut. Dysbiosis at the root of many chronic inflammatory diseases, including inflammatory bowel disease and rheumatoid arthritis.

How Is SpA Diagnosed?

Diagnosing SpA in general and AS and nr-axSpA in particular is challenging. There are no current diagnostic criteria for axSpA; the last update, called the New York criteria, was in 1966. The New York criteria rely heavily on X-ray findings, yet X-rays — and even MRI — aren’t always reliable or interpreted accurately. What’s more, the 1966 criteria dropped uveitis as a defining symptom, although it occurs in about at least one-third of patients with AS. Another concern is that lack of reliable diagnostic criteria may make it easier to mistake ordinary back pain for nr-axSpA, leading to unnecessary treatment.

The criteria from the European Spondylitis Study Group and Armor criteria perform better. To be diagnosed with SpA using the Armor criteria, a patient does not need a positive HLA-B27 test but must have other symptoms associated with SpA, such as heel or buttock pain or a family or personal history of inflammatory bowel disease or psoriasis. This family of diseases is still tricky to diagnose, however. Your best bet is a doctor who’s experienced with the many manifestations of SpA and has good clinical judgment.

How Is SpA Treated?

The first-line treatment for spine pain is nonsteroidal anti-inflammatories (NSAIDs) like naproxen, ibuprofen and celecoxib. For many people with AS or nr-axSpA, these drugs along with exercise are enough to control symptoms.

If you don’t get relief from NSAIDs or have severe peripheral arthritis, you and your doctor might consider a tumor necrosis factor (TNF) blocker like infliximab (Remicade), adalimumab (Humira) or certolizumab (Cimzia). Certolizumab is the only TNF inhibitor approved by the Food and Drug Administration (FDA) to treat nr-axSpA, but doctors prescribe the others off-label based on research and clinical experience. Another option is an interleukin (IL)-17 blocker like secukinumab (Cosentyx) or ixekizumab (Taltz), both FDA-approved for nr-axSpA. All of these medications, called biologics, are expensive and can have potentially serious side effects, so be sure you and your doctor weigh the pros and cons carefully.

Exercise is important for everyone with arthritis, but it’s a fundamental part of treatment if you have AS or nr-axSpA. It relieves pain better than medications and is the only way to keep your spine healthy and mobile. The American College of Rheumatology (ACR) recommends that everyone with axSpA get physical therapy and regularly perform exercises that “promote spine extension and mobility.” Swimming, in particular, is terrific for back health.

John Flynn, MD, a professor of medicine and director of the spondyloarthritis clinic at Johns Hopkins Medicine in Baltimore, touts the benefits of exercise, too. “I prescribe physical therapy for everyone,” he says, noting that exercise may slow disease progression.

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