Ankylosing Spondylitis vs Axial SpA: Treatment Differences

If your doctor calls it "ankylosing spondylitis" but your imaging report says "axial spondyloarthritis," you are not getting conflicting diagnoses — you are getting two names for conditions on the same spectrum. The treatment drugs are the same class. The treatment goals are the same. What differs is the diagnostic threshold: ankylosing spondylitis (AS) requires visible bone damage on X-ray, while nonradiographic axial spondyloarthritis (nr-axSpA) does not — and that distinction has real consequences for how quickly you get treated and what your insurance covers.

This explainer draws on peer-reviewed research from four rheumatologists listed in the Convene directory: Lianne Gensler, M.D., at UCSF, who co-authored the 2022 ASAS-EULAR international management guidelines and multiple ACR treatment recommendations for both conditions; Alan Kivitz, MD, at UPMC Altoona, who ran the pivotal placebo-controlled trials that established biologic therapy for AS; Arthur Kavanaugh, M.D., at UC San Diego, who co-authored the international "treat-to-target" framework used across all forms of spondyloarthritis; and Eric Ruderman, MD, at Northwestern, who published the first systematic US prevalence study of axial SpA using ASAS diagnostic criteria.

The spectrum: one disease, two stages

Axial spondyloarthritis is the umbrella term. It covers all inflammatory spine disease in this family, from patients with active inflammation on MRI but no X-ray damage (nr-axSpA) to patients with structural changes visible on plain X-ray (AS, also called radiographic axSpA).

The distinction matters because bone damage on X-ray takes years to appear. Many patients — women more often than men — have significant inflammation, pain, and functional loss before their X-rays show anything definitive. Under the older diagnostic framework, those patients went undiagnosed or waited years for treatment. The ASAS (Assessment of SpondyloArthritis International Society) criteria, now used worldwide, allow a diagnosis of nr-axSpA based on MRI evidence of sacroiliac inflammation or HLA-B27 positivity combined with clinical features, even without X-ray changes.

A 2013 study published in Arthritis Care & Research by Eric Ruderman and colleagues found that ASAS criteria and rheumatologist clinical judgment often do not align perfectly in practice, meaning patients in the US may still be classified inconsistently depending on which system their doctor uses [8]. Getting to a rheumatologist who applies current ASAS criteria matters.

At a glance

First-line treatment: NSAIDs for both

The 2022 ASAS-EULAR management recommendations — co-authored by Lianne Gensler and other international experts — set continuous NSAID therapy as the first treatment step for active axSpA, regardless of whether the patient has X-ray damage [1]. NSAIDs reduce pain and stiffness and, in some patients, may slow radiographic progression in AS with sustained use.

The 2019 ACR/SAA/SPARTAN recommendations, which Gensler also co-authored and which were published in both Arthritis Care & Research and Arthritis & Rheumatology, add that physical therapy should run alongside medications from the start [2]. Exercise keeps the spine mobile and slows the tendency toward stiffening that comes with long-standing AS.

If two different NSAIDs at adequate doses fail over four weeks each, the guidelines recommend moving to biologic therapy. This applies equally to AS and nr-axSpA — the threshold to escalate does not depend on X-ray status.

Biologic therapy: TNF inhibitors, IL-17 inhibitors, JAK inhibitors

All three biologic drug classes are used in both AS and nr-axSpA. The foundational evidence came from AS trials, then extended to the broader axSpA population.

TNF inhibitors

Alan Kivitz was a principal investigator on two landmark trials that established TNF inhibitor therapy for AS. A 2003 randomized controlled trial published in Arthritis & Rheumatism found etanercept significantly more effective than placebo for active AS [6]. A 2006 trial from the same journal showed adalimumab produced significant, sustained reductions in AS signs and symptoms over 24 weeks [5]. These trials, and others for infliximab and certolizumab, built the evidence base that TNF inhibitors now carry formal approval for both AS and nr-axSpA.

An important finding from a 2013 analysis co-authored by Gensler: TNF inhibitor treatment appears to slow radiographic progression in AS, with the strongest effect when treatment starts early and continues long-term [4]. This is one reason getting diagnosed — and getting to a biologic if NSAIDs fail — before structural damage accumulates matters for long-term outcomes.

IL-17 inhibitors and JAK inhibitors

Secukinumab and ixekizumab (IL-17A inhibitors) are approved for both AS and nr-axSpA. Bimekizumab, which blocks both IL-17A and IL-17F, received approval more recently. Tofacitinib and upadacitinib (JAK inhibitors) are approved for AS; regulatory approval for nr-axSpA has followed in some countries.

The 2022 ASAS-EULAR guidelines treat all three classes as equivalent options after NSAID failure, with no head-to-head evidence clearly favoring one over another [1]. Choice depends on comorbidities, cost, and whether the patient has other features like inflammatory bowel disease or uveitis that might favor a specific drug class.

Treat-to-target: the same goal for both conditions

The treat-to-target framework — reaching remission or low disease activity, not just tolerating symptoms — was formalized for spondyloarthritis in a 2013 international task force paper co-authored by Arthur Kavanaugh and published in the Annals of the Rheumatic Diseases [7]. A 2017 update of those recommendations extended the framework and reinforced that the target is the same whether the patient has AS or nr-axSpA [3].

In practice, this means your rheumatologist should be measuring disease activity at every visit using a standardized score (ASDAS or BASDAI are the most common), not just asking how you feel. If the score stays above target after an adequate trial of a drug, the recommendation is to switch — either to a different biologic or to a different class.

What the insurance and approval landscape looks like

One practical difference between AS and nr-axSpA is insurance coverage. Some biologics carry FDA approval for AS but not for nr-axSpA, or approval for nr-axSpA came years after AS. Prior authorization processes vary. Patients with nr-axSpA sometimes face more hurdles getting biologic coverage than AS patients do, even when their disease activity is identical.

This is shifting as more drugs receive nr-axSpA indications, and as payers become more familiar with the ASAS diagnostic framework. But if you have nr-axSpA and hit an insurance barrier, working with your rheumatologist to document objective disease activity (MRI findings, CRP, ASDAS score) tends to be the most effective approach.

What about conventional DMARDs?

Sulfasalazine, methotrexate, and leflunomide are conventional disease-modifying drugs widely used in rheumatoid arthritis. They do not work well for axial inflammation. The ACR/SAA/SPARTAN guidelines explicitly recommend against using them for the axial component of disease in both AS and nr-axSpA [2]. They may have some role if a patient also has peripheral joint involvement (knees, ankles, hips), but they are not a substitute for biologic therapy when the spine is the primary problem.

Corticosteroids (prednisone) are similarly not part of long-term management. Short courses for flares are sometimes used, but there is no evidence they modify disease course in axSpA, and long-term use carries well-documented risks.

Questions to ask your rheumatologist

• Do I have AS or nr-axSpA, and does the distinction affect which biologics my insurance will cover?
• Which disease activity score are you using to track my progress, and what is my target number?
• If my current NSAID is not controlling symptoms, how long should we try it before moving to a biologic?
• For biologics, is there a reason to prefer a TNF inhibitor over an IL-17 inhibitor or JAK inhibitor given my other health conditions?
• How often should we repeat imaging to check for structural progression?

The bottom line

Ankylosing spondylitis and axial spondyloarthritis are the same inflammatory disease at different stages of X-ray progression. Both are treated with NSAIDs first, then biologics — TNF inhibitors, IL-17 inhibitors, or JAK inhibitors — if NSAIDs do not control the disease. The treatment goal is the same for both: remission or low disease activity, measured objectively at every visit. The main practical differences are earlier diagnosis without waiting for X-ray damage, some variation in which biologic approvals apply, and potential insurance access barriers for nr-axSpA patients. Starting treatment before structural damage accumulates, particularly with a biologic when warranted, gives the best chance of preserving spinal mobility.