What is spondyloarthritis of the spine?

Spondyloarthropathy of the Spine

Spondyloarthropathy of the spine (axial spondyloarthritis) is a chronic inflammatory disorder affecting the sacroiliac joints and spine, characterized by inflammatory back pain, morning stiffness, and potential extra-musculoskeletal manifestations, which can significantly impair quality of life if not diagnosed and treated promptly. 1

Definition and Classification

Axial spondyloarthritis (axSpA) is the main form of chronic inflammatory arthritis affecting the axial skeleton and comprises a spectrum of inflammatory conditions including:

• Ankylosing spondylitis (radiographic axSpA)
• Non-radiographic axial spondyloarthritis
• Psoriatic spondyloarthritis
• Reactive arthritis
• Enteropathic spondyloarthritis (associated with inflammatory bowel disease)
• Juvenile spondyloarthritis
• Undifferentiated spondyloarthritis 1, 2

Epidemiology

• Prevalence: 0.9% to 1.4% in the United States adult population
• Global prevalence varies from 0.14% in Latin America to 0.25% in Europe 1
• Affects 0.1-0.5% of the population for ankylosing spondylitis specifically 3
• Strong genetic component with HLA-B27 positivity in 74-89% of patients 1

Clinical Features

Key Characteristics of Inflammatory Back Pain (present in 70-80% of patients):

• Insidious onset before age 45
• Symptoms lasting >3 months
• Morning stiffness >30 minutes
• Pain at night/early morning
• Improvement with exercise but not with rest
• Alternating buttock pain 1

Extra-articular Manifestations:

• Uveitis
• Psoriasis
• Inflammatory bowel disease 3, 1

Pathogenesis

The disease involves:

• Genetic predisposition (strong association with HLA-B27)
• Gut microbial dysbiosis
• Entheseal trauma
• Immune cell infiltration of the sacroiliac joints and entheseal insertion areas in the spine 1

Diagnostic Approach

Clinical Assessment:

• Inflammatory back pain pattern
• Extra-articular manifestations
• Family history
• Response to NSAIDs

Laboratory Tests:

• HLA-B27 testing (sensitivity 90-95% in ankylosing spondylitis)
• Inflammatory markers (ESR/CRP) may be elevated but normal levels don't rule out disease (sensitivity only 50%) 1

Imaging:

• Radiography of sacroiliac joints: first-line imaging looking for erosions, sclerosis, joint space narrowing, and ankylosis
• MRI of sacroiliac joints: can detect early inflammatory changes before radiographic damage
• Bone marrow edema on MRI is the hallmark of active sacroiliitis
• CT may help when radiographs are equivocal
• Spine imaging to assess for syndesmophytes in established disease 1

Disease Activity Assessment

• ASDAS-CRP (Ankylosing Spondylitis Disease Activity Score): combines patient-reported outcomes and CRP levels
• BASDAI (Bath Ankylosing Spondylitis Disease Activity Index): measures fatigue, pain, stiffness, and discomfort
• BASFI (Bath Ankylosing Spondylitis Functional Index): measures functional ability 1

Treatment

First-line Treatment:

• NSAIDs have long been used as first-line treatment 3
• Physical therapy and exercise to maintain spinal mobility

Biologic Therapy:

• TNF inhibitors (TNFi) are recommended over secukinumab or ixekizumab as the first biologic to be used 3
• Secukinumab or ixekizumab is recommended over a second TNFi in patients with primary non-response to the first TNFi 3
• TNFi, secukinumab, and ixekizumab are favored over tofacitinib 3

Other Medications:

• Sulfasalazine is recommended only for persistent peripheral arthritis when TNFi are contraindicated 3
• Co-administration of low-dose methotrexate with TNFi is not recommended 3

Treatment Strategy:

• A strict treat-to-target strategy is not recommended 3
• Discontinuation or tapering of biologics in patients with stable disease is not recommended 3

Monitoring

• Regular assessment of disease activity using validated tools
• For patients with unclear disease activity, spine or pelvis MRI could aid assessment
• Routine monitoring of radiographic changes with serial spine radiographs is not recommended 3

Prognosis and Complications

Without proper treatment, axSpA can lead to:

• Progressive spinal fusion and ankylosis
• Decreased mobility and function
• Reduced quality of life
• Work disability

Early diagnosis and appropriate treatment can significantly improve outcomes and prevent structural damage 4.

Common Pitfalls in Diagnosis

• Delayed diagnosis (average 7-10 years from symptom onset)
• Over-reliance on radiographs (missing early disease)
• Ignoring inflammatory back pain patterns
• Neglecting extra-articular manifestations
• Misinterpreting normal inflammatory markers
• Referring patients to inappropriate specialists 1

The concept of spondyloarthropathy has evolved significantly in recent decades, with improved understanding leading to earlier diagnosis and more effective treatments that can prevent disease progression and improve quality of life 4.