What is the diagnostic process for seronegative spondylarthropathies?

Diagnostic Process for Seronegative Spondyloarthropathies

The diagnosis of seronegative spondyloarthropathies requires a combination of clinical assessment, laboratory testing, and appropriate imaging studies, with MRI being the most sensitive tool for early detection of inflammatory changes before radiographic damage occurs. 1

Clinical Evaluation

Key Clinical Features to Identify

• Inflammatory back pain (onset before age 45, duration >3 months)
• Morning stiffness lasting >30 minutes
• Pain that improves with exercise but not rest
• Nocturnal awakening due to pain (especially in second half of night)
• Alternating buttock pain 1, 2
• Peripheral manifestations:
  • Enthesitis (inflammation at tendon/ligament insertions)
  • Dactylitis ("sausage digits")
  • Peripheral arthritis 1, 2
• Extra-articular manifestations:
  • Psoriatic plaques or nail changes
  • Eye inflammation (uveitis)
  • Inflammatory bowel disease symptoms 3

Laboratory Testing

• HLA-B27 testing (positive in many but not all cases)
  • Important: A negative HLA-B27 test does not rule out seronegative spondyloarthropathies 2
• C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR)
  • May be elevated but can be normal in up to 50% of cases 2
• Rheumatoid factor (RF) - negative by definition
• Anti-citrullinated protein antibodies (ACPA) - negative

Imaging Studies

Step 1: Radiography

• First-line imaging for suspected sacroiliitis 1
• Evaluate sacroiliac joints for:
  • Erosions
  • Joint space narrowing or widening
  • Sclerosis
  • Ankylosis 1
• For peripheral symptoms, obtain radiographs of hands and feet 2

Step 2: MRI (if radiographs are negative or equivocal)

• Most sensitive for early inflammatory changes before radiographic damage 1
• Protocol should include:
  • T1-weighted sequences
  • Fat-suppressed fluid-sensitive sequences (T2-weighted fat-suppressed or STIR)
  • Optional: Gadolinium contrast-enhanced T1-weighted fat-saturated sequences 1
• Key findings:
  • Bone marrow edema
  • Synovitis
  • Enthesitis
  • Erosions 1

Step 3: Additional Imaging (if needed)

• CT scan: Better for detecting subtle erosions and structural changes when MRI cannot be performed 1
• Ultrasound: Useful for peripheral joints to detect:
  • Synovial hypertrophy
  • Hyperemia on color Doppler
  • Erosions 1

Classification Criteria

CASPAR Criteria for Psoriatic Arthritis

• Established inflammatory arthritis with ≥3 points from:
  • Current psoriasis (2 points), history of psoriasis (1 point), or family history (1 point)
  • Nail dystrophy (1 point)
  • Negative rheumatoid factor (1 point)
  • Current or history of dactylitis (1 point)
  • Radiographic evidence of juxta-articular new bone formation (1 point) 1

ASAS Classification for Axial Spondyloarthritis

• Back pain ≥3 months, age of onset <45 years, plus either:
  • Sacroiliitis on imaging plus ≥1 SpA feature, OR
  • HLA-B27 positive plus ≥2 SpA features 1

Differential Diagnosis

• Rheumatoid arthritis (distinguished by symmetric polyarthritis, rheumatoid nodules, high RF titers) 1
• Osteoarthritis (distinguished by mechanical rather than inflammatory pattern) 1
• Mechanical back pain (lacks inflammatory features, morning stiffness) 1
• Diffuse idiopathic skeletal hyperostosis (DISH)
• Spinal fractures (consider in case of sudden change in symptoms) 1

Common Pitfalls to Avoid

1. Overlooking seronegative spondyloarthropathy due to negative HLA-B27 - The diagnosis should be based on clinical features and imaging, not solely on HLA-B27 status 2

2. Relying only on radiographs - Radiographic changes often lag behind clinical symptoms by 7+ years; MRI is essential for early diagnosis 1

3. Missing peripheral manifestations - Enthesitis and peripheral arthritis may be the predominant features in some patients 2

4. Failing to consider subtypes - Seronegative spondyloarthropathies include ankylosing spondylitis, psoriatic arthritis, reactive arthritis, enteropathic arthritis, and undifferentiated spondyloarthropathy 4

5. Overlooking extra-articular manifestations - Particularly uveitis, which requires immediate ophthalmology referral 2

By following this structured diagnostic approach and avoiding common pitfalls, clinicians can effectively diagnose seronegative spondyloarthropathies and initiate appropriate treatment to prevent disease progression and improve patient outcomes.