What is the diagnostic approach to polymyalgia rheumatica (PMR)?

Diagnostic Approach to Polymyalgia Rheumatica (PMR)

The diagnostic approach to polymyalgia rheumatica requires a combination of clinical assessment, laboratory testing, and exclusion of mimicking conditions, with ESR and CRP being essential inflammatory markers to support the diagnosis. 1, 2

Clinical Features to Assess

• Bilateral shoulder pain with morning stiffness lasting >45 minutes in patients >50 years old is the hallmark presentation 1, 3
• Functional impairment of the shoulder girdle with pain on movement 1, 4
• Pelvic girdle pain and stiffness (though not mandatory for diagnosis) 2, 5
• Constitutional symptoms including fatigue, low-grade fever, and weight loss may be present 4, 5
• Rapid onset of symptoms, developing over days to weeks 5

Core Laboratory Workup

• Essential inflammatory markers:

  • Erythrocyte sedimentation rate (ESR) - particularly valuable as high levels (>40 mm/1st hour) are associated with higher relapse rates 1, 6
  • C-reactive protein (CRP) 1, 2

• Autoantibody testing:

  • Rheumatoid factor and/or anti-cyclic citrullinated peptide antibodies (ACPA) to exclude rheumatoid arthritis 1, 2

• Basic laboratory panel:

  • Complete blood count to assess for anemia or other causes of inflammation 1
  • Basic metabolic panel including glucose, creatinine, and liver function tests 1
  • Bone profile (calcium, alkaline phosphatase) 1
  • Urinalysis 1

Additional Recommended Tests

• Protein electrophoresis to exclude paraproteinemia 1
• Thyroid stimulating hormone (TSH) to rule out thyroid disorders 1
• Creatine kinase to exclude myopathies and myositis 1, 4
• Vitamin D level as baseline before potential glucocorticoid therapy 1

Extended Testing Based on Clinical Presentation

• Anti-nuclear antibodies (ANA) and anti-cytoplasmic neutrophil antibodies (ANCA) when other autoimmune conditions are suspected 1
• Tuberculosis testing when immunosuppressive therapy is being considered 1
• Chest radiograph to exclude malignancy 1

Imaging Studies

• Ultrasound can detect bilateral subdeltoid bursitis in 69% of PMR patients 3
• MRI may reveal inflammation in proximal joints and periarticular structures 7
• Consider advanced imaging (ultrasound, MRI, PET-CT) in atypical presentations 5

Diagnostic Algorithm

1. Initial assessment:

   • Evaluate for bilateral shoulder pain, morning stiffness, functional impairment, age >50 years 1, 3
   • Order core laboratory tests with focus on inflammatory markers 1, 2

2. Differential diagnosis:

   • Exclude inflammatory arthritis (rheumatoid arthritis, spondyloarthropathies) 2, 4
   • Rule out endocrine disorders (thyroid disease) 1
   • Consider infections and malignancies 1, 2
   • Evaluate for other rheumatic conditions (fibromyalgia, osteoarthritis) 4

3. Therapeutic trial:

   • Consider response to low-dose glucocorticoids (12.5-25 mg prednisone equivalent) as a diagnostic tool 1, 2
   • Rapid improvement (within 24-72 hours) supports PMR diagnosis 2, 4

Special Considerations

• Consider specialist referral for atypical presentations including:

  • Peripheral inflammatory arthritis 1, 2
  • Systemic symptoms disproportionate to PMR 1, 2
  • Age <60 years 1, 2
  • Normal inflammatory markers 1, 6
  • High risk of treatment-related side effects 1, 2

• Always consider giant cell arteritis (GCA) in PMR patients who develop:

  • New-onset headache 3, 4
  • Visual disturbances or vision loss 3, 4
  • Scalp tenderness or temporal artery abnormalities 4

Common Pitfalls and Caveats

• No single test is pathognomonic for PMR; diagnosis remains primarily clinical 1
• PMR with normal inflammatory markers is rare but possible and warrants specialist evaluation 6
• Failure to respond to moderate-dose glucocorticoids should prompt reconsideration of diagnosis 2, 4
• Overlooking giant cell arteritis can lead to irreversible vision loss 3, 4
• PMR-like syndromes may develop as a side effect of cancer treatment with checkpoint inhibitors 5