What investigations are used to assess for Rheumatoid Arthritis (RA)?

Investigations for Rheumatoid Arthritis Assessment

A comprehensive diagnostic approach for rheumatoid arthritis should include laboratory tests (rheumatoid factor, anti-citrullinated protein antibodies, inflammatory markers), imaging studies (radiographs, ultrasound, MRI), and careful clinical assessment of joint involvement patterns. 1

Laboratory Investigations

Essential Serological Tests

• Rheumatoid Factor (RF): Sensitivity 69-84%, specificity 78-85% 1
• Anti-Citrullinated Protein Antibodies (ACPA/anti-CCP): Sensitivity 67-78.5%, specificity 95-98% - highest specificity for RA 1
• Inflammatory Markers:
  • Erythrocyte Sedimentation Rate (ESR)
  • C-Reactive Protein (CRP)
  • Should be performed at baseline and repeated when clinically relevant 2

Additional Laboratory Tests

• Complete Blood Count
• Liver Function Tests
• Renal Function Tests
• Urinalysis
• Antinuclear Antibodies (ANA) - if systemic lupus erythematosus is suspected
• Immunoglobulins
• Thyroid Function Tests 2

Imaging Studies

Conventional Radiography

• Plain radiographs of hands and feet (posteroanterior view) should be the initial imaging modality 1
• Useful for detecting:
  • Early changes: soft tissue swelling and juxtaarticular osteoporosis 3
  • Established disease: erosions, joint space narrowing
• Should be performed periodically (every 6-12 months in early disease) to monitor structural damage 1

Advanced Imaging

• Ultrasound:

  • Superior to clinical examination for detecting joint inflammation 2
  • Can detect synovitis and erosions not visible on radiographs 1
  • Particularly useful when there is doubt about the presence of inflammatory activity based on clinical assessment 2
  • Power Doppler ultrasound can help predict progression from undifferentiated inflammatory arthritis to RA 2

• Magnetic Resonance Imaging (MRI):

  • More sensitive than radiographs for detecting early erosions and synovitis 2
  • Can detect bone edema which predicts progression to RA 2
  • Consider when radiographs don't show damage but clinical suspicion remains high 1
  • MRI flexor tenosynovitis is a predictor of early RA 2

Clinical Assessment Tools

• Joint Examination:

  • Tender and swollen joint count
  • Pattern assessment: symmetrical involvement of small joints is characteristic 3
  • Morning stiffness duration (typically >1 hour in active disease) 3

• Disease Activity Measures:

  • Disease Activity Score (DAS28)
  • Simplified Disease Activity Index (SDAI)
  • Clinical Disease Activity Index (CDAI) 1

Diagnostic Pitfalls and Considerations

• Rule Out Mimicking Conditions:

  • Crystal arthropathies (gout, pseudogout)
  • Psoriatic arthritis
  • Spondyloarthritis
  • Systemic lupus erythematosus
  • Osteoarthritis
  • Fibromyalgia 2

• Special Considerations:

  • Comorbidities like obesity and fibromyalgia may complicate assessment 2
  • When traditional measures are challenging to interpret, ultrasound is the most feasible measure to detect inflammatory activity 2
  • Extra-articular manifestations may be present and require additional investigations 4

Diagnostic Algorithm

1. Initial Assessment:

   • Clinical evaluation focusing on joint pattern, morning stiffness, and extra-articular features
   • Laboratory tests: RF, ACPA, ESR, CRP
   • Plain radiographs of hands and feet

2. If Diagnosis Uncertain:

   • Ultrasound or MRI to detect subclinical synovitis
   • Additional laboratory tests to rule out mimicking conditions

3. For Disease Monitoring:

   • Regular assessment of disease activity using composite indices
   • Periodic radiographs to assess structural damage
   • Consider ultrasound or MRI when clinical assessment and composite indices are difficult to interpret

Remember that early diagnosis and treatment are crucial for preventing joint damage and disability in RA, but careful assessment is needed to avoid misdiagnosis 2.