What is the preferred marker, Erythrocyte Sedimentation Rate (ESR) or C-Reactive Protein (CRP), for diagnosing and monitoring Polymyalgia Rheumatica (PMR)?

ESR vs CRP for Polymyalgia Rheumatica (PMR)

Both ESR and CRP should be measured in the diagnostic evaluation of PMR, with CRP being a more sensitive indicator of current disease activity, though ESR is a superior predictor of relapse. 1, 2

Diagnostic Value of ESR and CRP in PMR

Initial Diagnosis

• Both ESR and CRP are important inflammatory markers in the diagnostic workup for PMR 3, 1
• Laboratory evaluation should include:
  • Complete blood count
  • ESR and CRP
  • Rheumatoid factor
  • Anti-cyclic citrullinated peptide antibodies
  • Basic biochemistry 1

Comparative Sensitivity

• CRP is more sensitive than ESR for detecting current disease activity:
  • Only 1% of PMR patients have normal CRP at diagnosis
  • 6% of PMR patients may have normal ESR at diagnosis 2
• CRP is elevated in 62% of relapse episodes where ESR is normal 2

Clinical Scenarios and Special Considerations

PMR with Normal Inflammatory Markers

• PMR can present with normal ESR (≤30 mm/h) in approximately 6-14% of patients 4, 2
• Patients with normal ESR but PMR typically:
  • Are younger at diagnosis
  • Have longer symptom duration before diagnosis
  • Have lower comorbidity rates
  • Are predominantly male 4, 5
• When ESR is normal, CRP is still elevated in 90% of these cases 2
• In rare cases where both ESR and CRP are normal (14% in one study), serum amyloid A (SAA) may be elevated and can be used as an alternative marker 4

Monitoring Disease Activity and Predicting Relapse

• ESR >40 mm/h at diagnosis has twice the relative risk (4.9) for predicting relapse compared to CRP >7.8 mg/dL (relative risk 2.1) 2
• CRP normalizes more quickly than ESR with effective treatment, making it more responsive to short-term changes in disease activity 2, 6

Recommendations for Clinical Practice

1. Initial Diagnosis:

   • Measure both ESR and CRP as part of the diagnostic workup
   • Do not exclude PMR diagnosis based on normal ESR alone
   • Consider ultrasound to demonstrate bursitis in patients with normal inflammatory markers 4

2. Disease Monitoring:

   • Use both ESR and CRP for monitoring disease activity
   • CRP is preferred for assessing immediate treatment response
   • ESR is more valuable for predicting long-term outcomes and relapse risk 2

3. Follow-up Schedule:

   • Monitor patients every 4-8 weeks in the first year
   • Every 8-12 weeks in the second year
   • Assess both clinical response and inflammatory markers 1

Pitfalls to Avoid

• Excluding PMR diagnosis solely based on normal ESR
• Failing to measure both ESR and CRP in the initial workup
• Not considering alternative inflammatory markers (like SAA) when both ESR and CRP are normal in clinically suspicious cases
• Relying exclusively on inflammatory markers without clinical correlation

Remember that response to low-dose glucocorticoids (15-20 mg/day of prednisone) with significant improvement within 24-72 hours remains a key confirmatory element of PMR diagnosis, regardless of baseline inflammatory marker levels 1, 7.