What is the diagnostic approach for rheumatoid arthritis?

Diagnostic Approach for Rheumatoid Arthritis

The diagnosis of rheumatoid arthritis requires the presence of at least one joint with definite clinical synovitis (swelling) not better explained by another disease, with a score of ≥6/10 on the 2010 ACR/EULAR classification criteria based on joint involvement, serology, acute phase reactants, and symptom duration. 1

Clinical Evaluation

Key Clinical Features to Assess

• Joint involvement pattern:

  • Small joint involvement (MCPs, PIPs, wrists) is more characteristic than large joint involvement 1
  • Symmetric distribution is typical 2
  • "Squeeze test" of MCP or MTP joints (positive test indicates inflammation) 3

• Duration and timing of symptoms:

  • Morning stiffness lasting at least 1 hour 2
  • Symptoms lasting ≥6 weeks score higher in classification criteria 1

• Systemic symptoms:

  • Fatigue, low-grade fever, weight loss, malaise 2

Laboratory Testing

First-line Tests

• Serology:

  • Rheumatoid Factor (RF): Moderate specificity (70%) 1
  • Anti-citrullinated protein antibody (ACPA): Higher specificity (90%) 1
  • Scoring for serology in classification criteria:
    • Negative RF and negative ACPA: 0 points
    • Low-positive RF or low-positive ACPA: 2 points
    • High-positive RF or high-positive ACPA: 3 points 3

• Inflammatory markers:

  • C-reactive protein (CRP): Preferred over ESR due to simplicity, reliability, and age-independence 1
  • Erythrocyte sedimentation rate (ESR): Alternative to CRP 1
  • Abnormal CRP or ESR: 1 point in classification criteria 1

• Additional baseline tests:

  • Complete blood count with differential
  • Renal and hepatic function tests 4
  • Hepatitis B, hepatitis C, and tuberculosis screening (if considering biologic therapy) 4

Imaging Studies

• Plain radiographs of hands and feet:

  • Early findings: Soft tissue swelling and juxtaarticular osteoporosis 2
  • Later findings: Erosions and joint space narrowing 3

• Advanced imaging when clinical examination is inconclusive:

  • Ultrasound: Detects synovitis, tenosynovitis, and erosions not visible on examination 1, 2
  • MRI: Identifies early synovitis and bone edema 1

2010 ACR/EULAR Classification Criteria

A score of ≥6/10 is required for definitive classification of RA:

1. Joint involvement (0-5 points):

   • 1 large joint: 0 points
   • 2-10 large joints: 1 point
   • 1-3 small joints: 2 points
   • 4-10 small joints: 3 points

   • 10 joints (at least 1 small joint): 5 points 1

2. Serology (0-3 points):

   • Negative RF and ACPA: 0 points
   • Low-positive RF or ACPA: 2 points
   • High-positive RF or ACPA: 3 points 1

3. Acute phase reactants (0-1 points):

   • Normal CRP and ESR: 0 points
   • Abnormal CRP or ESR: 1 point 1

4. Duration of symptoms (0-1 points):

   • <6 weeks: 0 points
   • ≥6 weeks: 1 point 1

Diagnostic Algorithm

1. Initial assessment:

   • Identify patients with at least one swollen joint not explained by another condition
   • Assess for symmetric small joint involvement
   • Evaluate duration of morning stiffness

2. Laboratory testing:

   • Order RF, ACPA, CRP (preferred) or ESR
   • Complete baseline blood work (CBC, renal/hepatic function)

3. Apply classification criteria:

   • Calculate score using joint involvement, serology, acute phase reactants, and symptom duration
   • Score ≥6/10 indicates RA

4. Imaging:

   • Obtain baseline radiographs of hands and feet
   • Consider ultrasound or MRI if clinical suspicion is high but diagnosis is uncertain

5. Referral:

   • Refer to rheumatologist ideally within 6 weeks of symptom onset 3
   • Early referral and treatment significantly improve long-term outcomes 3

Common Pitfalls to Avoid

• Delayed referral while waiting for laboratory confirmation 3
• Assuming hand stiffness in older adults is always due to osteoarthritis 3
• Overlooking RA in patients with only one or few affected joints initially 1
• Missing early disease by relying solely on radiographs, which may be normal in early RA 2
• Failing to distinguish between morning stiffness due to RA versus osteoarthritis (RA typically >1 hour) 2

Early diagnosis and prompt treatment with disease-modifying antirheumatic drugs are crucial to prevent joint damage, maintain function, and improve long-term outcomes 4, 5.