Diagnostic Testing for Polymyalgia Rheumatica (PMR)
There is no specific autoimmune test that is pathognomonic for PMR; diagnosis relies on a combination of clinical features, laboratory evidence of inflammation, exclusion of mimicking conditions, and response to glucocorticoid therapy. 1, 2
Core Laboratory Tests for PMR Diagnosis
- Inflammatory markers are essential: ESR and/or CRP should be measured, as they are elevated in >90% of PMR patients, with high ESR (>40 mm/1st hour) associated with higher relapse rates 2, 3
- Rheumatoid factor and/or anti-cyclic citrullinated peptide antibodies (ACPA) testing helps exclude rheumatoid arthritis, which commonly mimics PMR 1, 2
- Complete blood count is necessary to assess for other causes of inflammation or anemia 2
- Basic metabolic panel (glucose, creatinine, liver function tests) establishes baseline values before initiating glucocorticoid therapy 1
- Bone profile including calcium and alkaline phosphatase should be checked to assess bone health before steroid therapy 1, 2
- Urinalysis helps exclude other inflammatory or infectious conditions 2
Additional Recommended Tests
- Protein electrophoresis to exclude paraproteinemia which can mimic PMR symptoms 2
- Thyroid stimulating hormone (TSH) to rule out thyroid disorders presenting with similar symptoms 2
- Creatine kinase to exclude myopathies and myositis 2, 4
- Vitamin D level establishes a baseline before potential glucocorticoid therapy 2
Extended Testing Based on Clinical Presentation
- Anti-nuclear antibodies (ANA) and anti-cytoplasmic neutrophil antibodies (ANCA) should be considered when other autoimmune conditions are suspected 1, 2
- Tuberculosis testing is necessary when immunosuppressive therapy is being considered 1
- Imaging studies such as ultrasonography can help confirm diagnosis by demonstrating bursitis, even in patients with normal inflammatory markers 5
Important Clinical Considerations
- PMR can occur with normal ESR and CRP values (approximately 14-20% of cases), particularly in younger patients with longer symptom duration and lower comorbidity rates 6, 5
- In patients with normal ESR/CRP but clinical suspicion of PMR, serum amyloid A (SAA) may be elevated and can serve as an alternative inflammatory marker 5
- PMR has a complex relationship with other autoimmune conditions, particularly giant cell arteritis (occurs in approximately 20% of PMR cases) 3, 7
- Response to low-dose glucocorticoids (12.5-25 mg prednisone equivalent daily) is considered a diagnostic criterion for PMR 1, 2
Common Pitfalls to Avoid
- Relying solely on ESR/CRP for diagnosis may miss PMR cases with normal inflammatory markers 6, 5
- Failing to exclude mimicking conditions, particularly elderly-onset rheumatoid arthritis, which is frequently misdiagnosed as PMR 3
- Not considering specialist referral for atypical presentations (peripheral inflammatory arthritis, systemic symptoms, age <60 years) 1
- Overlooking the possibility of subclinical giant cell arteritis in PMR patients, which may require different management 7