What tests are used to diagnose Polymyalgia Rheumatica (PMR)?

Diagnostic Tests for Polymyalgia Rheumatica (PMR)

The diagnosis of PMR requires a core laboratory dataset including erythrocyte sedimentation rate (ESR) and/or C-reactive protein (CRP), rheumatoid factor and/or anti-cyclic citrullinated peptide antibodies, complete blood count, and basic metabolic panel 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 1, 2
• Autoantibody testing: Rheumatoid factor and/or anti-cyclic citrullinated peptide antibodies (ACPA) help exclude rheumatoid arthritis 1, 3
• Complete blood count: Necessary to assess for other causes of inflammation or anemia 1
• Basic metabolic panel: Including glucose, creatinine, and liver function tests to establish a 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

• Creatine kinase: To exclude myositis and other myopathies which can present with similar symptoms 1, 3
• 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
• Vitamin D: To establish a baseline before potential glucocorticoid therapy 1

Imaging Studies

• Ultrasound: Enables detection of bilateral subdeltoid bursitis in 69% of PMR patients, improving diagnostic accuracy 1, 4
• Magnetic resonance imaging (MRI): Can help identify inflammation in shoulder and hip joints 4

Extended Testing Based on Clinical Presentation

• Serological tests: Anti-nuclear antibodies (ANA) and anti-neutrophil cytoplasmic antibodies (ANCA) when other autoimmune conditions are suspected 1
• Tuberculosis testing: When immunosuppressive therapy is being considered or in high-risk patients 1
• Chest radiographs: To exclude other diagnoses like malignancy 1

Diagnostic Approach Algorithm

1. Initial clinical assessment: Look for bilateral shoulder pain, morning stiffness, functional impairment, and age >50 years 1, 4
2. Laboratory testing: Order the core laboratory tests listed above 1
3. Imaging: Consider ultrasound to detect subdeltoid bursitis 1, 4
4. Therapeutic trial: Response to low-dose glucocorticoids (12.5-25 mg prednisone equivalent) can be used as a diagnostic tool 1, 5
5. Differential diagnosis: Exclude mimicking conditions (inflammatory arthritis, endocrine disorders, infections, malignancies) 1, 6

Special Considerations

• Giant cell arteritis (GCA): Should be ruled out in all PMR patients, as it occurs in approximately 20% of PMR cases 7
• Atypical presentations: 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
• Normal inflammatory markers: PMR with normal inflammatory markers is considered an atypical presentation that warrants specialist referral 2

Pitfalls and Caveats

• No single test is pathognomonic for PMR; diagnosis remains primarily clinical, supported by laboratory evidence of inflammation and exclusion of other disorders 1, 4
• Elderly-onset rheumatoid arthritis is frequently misdiagnosed as PMR and should be carefully excluded 7
• ESR is particularly important in PMR diagnosis and monitoring, with high ESR (>40 mm/1st hour) being an independent risk factor for relapse 2
• When GCA is suspected, temporal artery biopsy remains the gold standard for definitive diagnosis, but imaging studies like ultrasound and MRI can support the diagnosis 3, 4