What are the differences between axial spondyloarthropathy (ankylosing spondylitis) and peripheral spondyloarthritis, including their clinical manifestations and recommended treatments?

Axial vs Peripheral Spondyloarthropathy: Key Distinctions

Axial spondyloarthropathy (axSpA) primarily affects the spine and sacroiliac joints with inflammatory back pain, while peripheral spondyloarthropathy (pSpA) predominantly involves peripheral joints, entheses, and dactylitis—though both share similar extra-articular manifestations and require distinct treatment approaches based on their dominant clinical pattern.

Clinical Manifestations

Axial Spondyloarthropathy

Axial disease is characterized by 1:

• Inflammatory back pain with sacroiliitis and potential spinal fusion
• Male predominance (70.4% in AS) 2
• Chronic back pain and spinal stiffness as primary symptoms
• Validated assessment using BASDAI plus acute phase reactants or ASDAS 3
• MRI inflammation of sacroiliac joints or radiographic sacroiliitis 4

Peripheral Spondyloarthropathy

Peripheral disease manifests as 3, 5:

• Asymmetric arthritis (prevalence ~28-30%)
• Enthesitis (prevalence ~29-35%)
• Dactylitis (prevalence ~6%)
• More balanced gender distribution (46.8% male) 2
• Greater working disability compared to axial disease 5

Shared Features

Both forms demonstrate similar prevalence of 2:

• HLA-B27 positivity (~77-78%)
• Psoriasis (~10%)
• Inflammatory bowel disease (~4-6%)
• Uveitis is more common in axial disease (23% vs 16%)

Treatment Differences

Axial Spondyloarthropathy Treatment Algorithm

Step 1: First-line therapy 1, 4:

• Continuous NSAIDs are strongly recommended as initial pharmacological treatment
• Physical therapy and regular exercise are essential non-pharmacological interventions
• Monitor disease activity with ASDAS or BASDAI plus CRP

Step 2: Biologic escalation 6, 4:

• Initiate TNF inhibitors or IL-17 inhibitors when ASDAS ≥2.1 persists despite ≥2 NSAIDs AND patient has either elevated CRP, MRI sacroiliac inflammation, or radiographic sacroiliitis
• TNFi is preferred as first biologic over IL-17i or JAK inhibitors 6
• No role for conventional DMARDs (methotrexate, sulfasalazine) in pure axial disease 7
• Avoid systemic glucocorticoids for axial manifestations 1

Step 3: Treatment failure management 6, 4:

• If primary non-response to first TNFi: switch to secukinumab or ixekizumab (IL-17i)
• If secondary failure: switch to another biologic with same or different mechanism
• JAK inhibitors reserved when biologics contraindicated or unavailable 8

Peripheral Spondyloarthropathy Treatment Algorithm

Step 1: Oligoarticular disease 9:

• NSAIDs and local glucocorticoid injections for symptomatic relief
• Consider short-term NSAID monotherapy (≤4 weeks) only for very mild disease

Step 2: Polyarticular or poor prognostic factors 9:

• Initiate csDMARD rapidly (methotrexate preferred if concomitant skin involvement)
• Poor prognostic factors include: structural damage, elevated acute phase reactants, dactylitis, nail involvement

Step 3: Biologic escalation 7:

• Sulfasalazine may be considered for persistent peripheral arthritis 7, 8
• When inadequate response: proceed to TNFi, IL-17i, or JAK inhibitors using similar algorithm as axial disease
• Methotrexate has no proven efficacy for axial symptoms but can be used for peripheral arthritis 7

Critical Treatment Distinctions

Key Differences to Remember:

1. DMARDs role: Conventional DMARDs (sulfasalazine, methotrexate) have NO efficacy for axial disease but may benefit peripheral arthritis 7, 8

2. Glucocorticoids: Local injections acceptable for peripheral manifestations; systemic glucocorticoids NOT supported for axial disease 7

3. Extra-articular manifestations guide biologic choice 6, 8:

   • Recurrent uveitis or IBD: Use TNF monoclonal antibodies (not etanercept)
   • Significant psoriasis: IL-17 inhibitors preferred
   • No specific extra-articular features: Any TNFi or IL-17i acceptable

4. Disease monitoring differs 3:

   • Axial: BASDAI/ASDAS with acute phase reactants, consider MRI for unclear activity
   • Peripheral: Quantified measures of arthritis, dactylitis, enthesitis

Common Pitfalls to Avoid

• Do not use methotrexate or sulfasalazine monotherapy for pure axial disease—this delays effective treatment 7
• Do not require DMARD failure before biologics in axial disease—no evidence supports this approach 7
• Do not discontinue biologics abruptly in remission—taper gradually if considering optimization 6, 4
• Do not ignore time to referral—axial patients often have longer symptom duration before diagnosis compared to peripheral patients 5

Both axial and peripheral SpA require treat-to-target strategies with regular disease activity monitoring and therapy adjustment to achieve remission or low disease activity, maximizing long-term quality of life and preventing structural damage 3, 10.