What tests are used to diagnose polymyalgia rheumatica (PMR)?

Diagnostic Tests for Polymyalgia Rheumatica (PMR)

The diagnosis of polymyalgia rheumatica requires a basic laboratory dataset including rheumatoid factor and/or anti-cyclic citrullinated peptide antibodies, C-reactive protein and/or erythrocyte sedimentation rate, complete blood count, glucose, creatinine, liver function tests, bone profile, and urinalysis to exclude mimicking conditions. 1

Core Laboratory Tests

• Inflammatory markers: ESR and/or CRP are essential, with ESR being particularly valuable as high levels (>40 mm/1st hour) are associated with higher relapse rates and may guide initial treatment decisions 2, 3
• Autoantibody testing: Rheumatoid factor and/or anti-cyclic citrullinated peptide antibodies (ACPA) to help exclude rheumatoid arthritis 1
• Complete blood count: To assess for other causes of inflammation or anemia 1
• Basic metabolic panel: Including glucose, creatinine, and liver function tests to establish baseline before glucocorticoid therapy 1
• Bone profile: Including calcium and alkaline phosphatase to assess bone health before steroid therapy 1
• Urinalysis: To exclude other inflammatory or infectious conditions 1

Additional Recommended Tests

• Protein electrophoresis: To exclude paraproteinemia which can mimic PMR symptoms 1
• Thyroid stimulating hormone (TSH): To rule out thyroid disorders that may present with similar symptoms 1
• Creatine kinase: To exclude myopathies and myositis 1
• Vitamin D: To establish baseline before potential glucocorticoid therapy 1

Extended Testing Based on Clinical Presentation

• Serological tests: Anti-nuclear antibodies (ANA), anti-cytoplasmic neutrophil antibodies (ANCA) when other autoimmune conditions are suspected 1
• Tuberculosis testing: When immunosuppressive therapy is being considered or in high-risk patients 1
• Imaging studies: Chest radiographs may be considered to exclude other diagnoses such as malignancy 1
• Ultrasound imaging: Can detect bilateral subdeltoid bursitis in approximately 69% of PMR patients, improving diagnostic accuracy 4, 5

Diagnostic Approach Algorithm

1. Initial evaluation: Assess for bilateral shoulder pain, morning stiffness, functional impairment, and age >50 years 4, 3
2. Laboratory testing: Order core laboratory tests listed above 1
3. Imaging consideration: Consider ultrasound of shoulders to detect subdeltoid bursitis 4, 5
4. Differential diagnosis: Exclude mimicking conditions (inflammatory arthritis, endocrine disorders, infections, malignancies) 1
5. Therapeutic trial: Consider response to low-dose glucocorticoids (12.5-25 mg prednisone equivalent) as a diagnostic tool 1, 3

Special Considerations

• PMR with normal inflammatory markers is considered an atypical presentation requiring specialist referral 2, 3
• Consider specialist referral for atypical presentations, including peripheral inflammatory arthritis, systemic symptoms, age <60 years, or when there's high risk of treatment-related side effects 1
• No single test is pathognomonic for PMR; diagnosis remains primarily clinical, supported by laboratory evidence of inflammation and exclusion of other disorders 6, 7
• The 2012 EULAR/ACR classification criteria can support diagnosis but are primarily intended for research purposes 6, 5

Common Pitfalls

• Relying solely on ESR/CRP without considering the full clinical picture 2, 3
• Failing to exclude other conditions that can mimic PMR, particularly giant cell arteritis, rheumatoid arthritis, and malignancy 4, 5
• Not considering atypical presentations that may require more extensive workup 1, 2
• Initiating treatment without establishing an adequate baseline for monitoring therapy 1