Let's start with the word itself, because it confuses people, including patients who have one of these conditions.
Spondyloarthritis literally means inflammation of the spine. But the term has come to describe a group of related autoimmune conditions that share certain features, only some of which involve the spine. It also sounds a lot like spondylosis (age-related wear-and-tear changes in the spine) or spondylolisthesis (slippage of one vertebra over another). Those are mechanical, structural problems. Spondyloarthritis is an inflammatory, immune-mediated disease.
To make things more confusing, many people with spondyloarthritis never have spine involvement at all.
This is the first in a series of posts on this group of conditions. Today's post is the overview. In the coming weeks, I'll go through each condition in more detail.
The four main types
There are four main conditions under the spondyloarthritis umbrella:
- Psoriatic arthritis (PsA). Inflammatory arthritis in patients with psoriasis or a close family history of psoriasis. Usually the psoriasis comes first.
- Ankylosing spondylitis (AS) / axial spondyloarthritis. Starts at a young age, usually begins in the sacroiliac (SI) joints, and migrates up the spine over time.
- Reactive arthritis. Joint inflammation triggered by an infection somewhere else in the body, usually a GI or genitourinary infection. Often self-limited, but not always.
- IBD-associated arthritis. Joint inflammation occurring in patients with inflammatory bowel disease (Crohn's or ulcerative colitis).
I'll dedicate a full post to each one over the next several weeks.
And then there's undifferentiated spondyloarthritis
There's a fifth group that doesn't fit neatly into any of those four categories. We call this undifferentiated spondyloarthritis.
These patients present in the same pattern as the other spondyloarthritides but don't have a defining feature that puts them into one of the other four categories. I usually treat them like psoriatic arthritis until it declares itself, if it ever does.
What makes spondyloarthritis different from rheumatoid arthritis
Honestly, I don't get many questions about spondyloarthritis. The term isn't well known. Most people lump everything into RA. But these are distinct conditions, and treatment can differ in meaningful ways.
A few of the differences:
- Pattern of joint involvement. Spondyloarthritis tends to be asymmetric and often involves fewer joints. RA is classically symmetric and involves the small joints of the hands and feet.
- Spine and sacroiliac joints. Commonly involved in spondyloarthritis, especially in ankylosing spondylitis. RA almost never affects them.
- Enthesitis. Inflammation where tendons attach to bone. This is a hallmark of spondyloarthritis and not really a feature of RA. Patients often describe it as heel pain or pain where a tendon meets bone.
- Dactylitis. A whole finger or toe diffusely swollen, often called a "sausage digit." Specific to spondyloarthritis.
- Extra-articular manifestations. Spondyloarthritis is associated with psoriasis, uveitis, and inflammatory bowel disease. RA has its own extra-articular features, but they're different.
- Lab findings. RA typically has positive serologies (rheumatoid factor, anti-CCP). Spondyloarthritis is usually seronegative.
A word on HLA-B27
HLA-B27 is a genetic marker that comes up a lot in this conversation. It's a gene that's strongly associated with spondyloarthritis, particularly ankylosing spondylitis.
Here's the important nuance: a positive HLA-B27 isn't a diagnosis. Many more people carry the marker than ever develop a spondyloarthritis. In the general population, about 6 to 8 percent of people are HLA-B27 positive. Most of them are completely fine.
What HLA-B27 does is raise the suspicion when someone has the right clinical picture. If a young patient comes in with inflammatory back pain that improves with movement, and they're HLA-B27 positive, that's meaningful. If they come in with mechanical low back pain from lifting boxes, the HLA-B27 doesn't change anything.
It's a piece of the puzzle, not the whole answer.
Why this matters
Spondyloarthritis is common, often missed, and very treatable when caught early. Like other inflammatory arthritis, it can cause joint damage and disability if not controlled. And like other autoimmune conditions, it's a clinical diagnosis that comes from putting the full picture together.
A few things that should raise the question of spondyloarthritis:
- Young patient with chronic back pain that's worse in the morning and better with movement
- Someone with psoriasis who develops joint pain or swelling
- Heel pain that won't go away
- A swollen finger or toe with no obvious injury
- Joint pain in someone with inflammatory bowel disease
What's coming
Over the next several weeks, I'll dedicate a post to each subtype:
- Psoriatic arthritis
- Ankylosing spondylitis and axial spondyloarthritis
- Reactive arthritis
- IBD-associated arthritis
- Undifferentiated spondyloarthritis
I'll touch on treatment in each post, because there are some nuances between the different conditions.
The bottom line
Spondyloarthritis is a group of related but distinct conditions. The word is confusing. The conditions don't always look alike. But they share enough common features (especially seronegative inflammatory arthritis, enthesitis, dactylitis, and certain extra-articular manifestations) that grouping them together makes clinical sense.
If you have a personal or family history of psoriasis, inflammatory bowel disease, uveitis, or chronic inflammatory back pain, and you're dealing with joint symptoms, a rheumatology evaluation is worth it. These conditions are treatable, especially when caught early.