A woman with axial spondyloarthritis stares blankly as scribbles pass through her ears.

Confusing Invisible Illness Terminology

There are lots of Spondy terms out there — some recently changed, some used correctly, some used incorrectly, some used half-correctly, and some undecided upon by the powers that be (medical pros, mostly).

Axial spondyloarthritis (axial SpA or AxSpA) is a new umbrella term (because why not make things more complicated in a group of diseases that already have so little visibility?) that has only recently found its way into rheumatologist offices, leaving even some medical professionals trying to find an easy way of saying all of those...complicated sounds (just read this 2019 paper by a doctor explaining what AxSpA is). A lot of people used to refer to it simply as ankylosing spondylitis, which isn't necessarily wrong (more on that below).

That said, the diseases AxSpA encompasses have been around for a long time, well before the new fancy name. For example, ankylosing spondylitis, one of the diseases under the AxSpA umbrella, has been called so many things: Bekhterev's disease, Bechterew's disease, morbus Bechterew, Bekhterev–Strümpell–Marie disease, Marie's disease, Marie–Strümpell arthritis, Pierre–Marie's disease.1,2Whaaaaaaat?

More on this topic

I'm going to try and clear up some of these confusing terms — only because it took me forever to figure it out, and even now I mess it all up sometimes.

What is spondyloarthritis?

Spondyloarthritis (also called spondylitis or SpA) is referred to by two different classification systems:

The traditional SpA classification system:

This system acknowledges six diseases: Enteropathic arthritis (EnA), psoriatic arthritis (PsA), ankylosing spondylitis (AS), reactive arthritis (ReA), juvenile spondyloarthritis (JSpA), and undifferentiated spondyloarthritis (USpA).2 You might hear people referring to these, or you might here the below definitions.

The newer SpA classification system:

This system recognizes two broad categories.

The first is axial spondyloarthritis (AxSpA). This contains ankylosing spondylitis (or radiographic AxSpA, which means you can see damage on an x-ray) and non-radiographic AxSpA (nr-AxSpA). Nr-AxSpA can become ankylosing spondylitis (AS), but not always.3

The second category under The Newer SpA Classification System is peripheral spondyloarthritis (pSpA). This is all about inflammation outside of the sacroiliac joints, which affects the axial spondyloarthritis (AxSpA) categories. These include enteropathic arthritis (EnA), reactive arthritis (ReA), psoriatic arthritis (PsA), and undifferentiated spondyloarthritis (USpA). Notice how in the new system ankylosing spondylitis was put into the AxSpA category for radiographic AxSpA.3

Yeah, I know. I know. It's a LOT.

The other terms

Then there are all the myriad words people use to describe these diseases. I'm not a doctor, but I'm a wellness writer and editor and have secured my information from sites like the one you're reading as well as the Spondylitis Association of American, recent medical journal publications, and the Mayo Clinic (full list of sources are listed at the bottom of this article).

"Autoimmune disease" vs "autoinflammatory" vs "immune-mediated:" This always confused me, so I wanted to share a bit about the terminology here. Buckle up here; we're gonna have a brief science lesson:

An autoimmune disease refers to conditions or diseases stemming from the immune system mistakenly attacking the body. Many people refer to AxSpA as an "autoimmune disease" (and it's been called for that a long time) but studies and medical professionals are not so sure.

It has also been referred to (rather vaguely) "immune in nature,"4 and as an "inflammatory rheumatic disease"5 or "autoinflammatory."6 The latter refers to "heritable disorders that are characterized by seemingly unprovoked episodes of inflammation and relative lack of obvious autoimmune pathology."6

In fact, in order to be classified as "autoimmune," autoantibodies must be detected7 — but autoantibodies are not typically associated with the AxSpA diseases. This is why one doctor said that it's probably more correct to classify AxSpA as both autoimmune and autoinflammatory since the immune system is involved.7

Some doctors call it immune-mediated, which refers to conditions or diseases that lack a definitive etiology (or cause or origin) but are characterized by inflammation that could have resulted from a deviation in a normal immune response.7


That was a lot. I hope this helps to clarify some of the terminologies you have seen in articles, reports, and at the docs' office. I know I could have used a handy pamphlet when I was first diagnosed.

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