What is the recommended treatment for ankylosing spondylitis in dogs?

Treatment for Ankylosing Spondylitis

Start with NSAIDs as first-line therapy, and if inadequate response after 2 NSAIDs, escalate to TNF inhibitors (TNFi) for patients with objective evidence of inflammation (elevated CRP, MRI inflammation, or radiographic sacroiliitis) and disease activity score ≥2.1. 1, 2

Treatment Algorithm by Disease Activity

Active Disease - First-Line Treatment

• NSAIDs are strongly recommended as initial pharmacological therapy 1
• Continuous NSAID therapy is preferred over on-demand dosing for better disease control 1
• No specific NSAID is superior to another - choose based on patient tolerance and response 1
• Physical therapy emphasizing consistent exercise, stretches, and posture maintenance should be initiated concurrently 3

Active Disease Despite NSAIDs - Second-Line Treatment

TNF inhibitors are the preferred biologic therapy when NSAIDs fail 1, 2:

• Options include: infliximab, etanercept, adalimumab, certolizumab, golimumab, and their biosimilars 1
• No particular TNFi is preferred - all are equally effective 1
• Eligibility criteria: Disease activity score (ASDAS) ≥2.1 AND failure of ≥2 NSAIDs AND objective inflammation (elevated CRP, MRI sacroiliitis, or radiographic sacroiliitis) 2

IL-17 inhibitors (secukinumab or ixekizumab) are also strongly recommended as second-line options 1:

• TNFi are conditionally preferred over IL-17 inhibitors for initial biologic therapy 1
• IL-17 inhibitors are conditionally preferred over tofacitinib (JAK inhibitor) 1

Conventional synthetic DMARDs (sulfasalazine, methotrexate) have limited role:

• Only consider for prominent peripheral arthritis or when biologics are unavailable 1
• Should NOT be used for pure axial disease 2
• Tofacitinib may be considered but is inferior to TNFi 1

Active Disease Despite First TNFi - Third-Line Treatment

The approach depends on the type of TNFi failure:

Primary non-response (no improvement within 3-6 months):

• Switch to IL-17 inhibitor (secukinumab or ixekizumab) - conditionally preferred over switching to another TNFi 1

Secondary non-response (loss of response after initial improvement):

• Switch to a different TNFi - conditionally preferred over non-TNFi biologics 1

Important caveats:

• Do NOT switch to a biosimilar of the same TNFi that failed 1
• Do NOT add sulfasalazine or methotrexate to the failing TNFi - switch to a new biologic instead 1
• Do NOT add low-dose methotrexate to TNFi for axial disease 1

Tailoring Treatment for Extra-Articular Manifestations

When extramusculoskeletal features are present 2:

• Recurrent uveitis or inflammatory bowel disease: Use TNF monoclonal antibodies (infliximab, adalimumab, certolizumab, golimumab) - NOT etanercept
• Significant psoriasis: IL-17 inhibitors are preferred

This is critical because etanercept is less effective for uveitis and IBD, while TNF monoclonal antibodies effectively treat all three conditions.

Stable Disease Management

For patients stable on TNFi for ≥6 months 1:

• Continue TNFi monotherapy
• Stop NSAIDs if disease is well-controlled 1
• Stop any concurrent conventional DMARDs 1
• Consider tapering (not abrupt discontinuation) of biologics in sustained remission 2
• If on originator TNFi and stable, do not switch to biosimilar for non-medical reasons 1

Treatment Failure Considerations

Before escalating therapy, always 2:

• Re-evaluate the diagnosis to confirm axSpA
• Assess for comorbidities (fibromyalgia, mechanical back pain, osteoarthritis)
• Verify medication adherence
• Confirm presence of active inflammation (not just pain)

Treatments to AVOID

• Long-term glucocorticoids - discouraged for axial disease 2
• Conventional DMARDs for pure axial involvement - ineffective 2
• Biosimilar switching after failure of originator TNFi 1
• Adding methotrexate or sulfasalazine to failing TNFi instead of switching biologics 1

Key Monitoring Parameters

Active disease is defined as symptoms at an unacceptably bothersome level judged by the clinician to be due to inflammation 1. Monitor treatment response at 3-6 months, as primary non-response is defined by lack of meaningful improvement in this timeframe 1.

The evidence base from the 2019 ACR/SAA/SPARTAN guidelines [1-1] and 2022 ASAS-EULAR update 2 provides high-quality guidance for TNFi and IL-17 inhibitors, with moderate-to-high quality evidence supporting their efficacy in reducing disease activity and improving quality of life.