What is the diagnostic approach for Polymyalgia Rheumatica (PMR)?

Diagnostic Approach for Polymyalgia Rheumatica (PMR)

The diagnosis of polymyalgia rheumatica requires a systematic exclusion of mimicking conditions through comprehensive clinical evaluation, laboratory testing, and in some cases, imaging studies.

Clinical Presentation Assessment

• Age requirement: PMR almost exclusively affects patients over 50 years of age 1
• Cardinal symptoms:
  • Bilateral shoulder pain/aching (most common presentation)
  • Morning stiffness lasting >30 minutes
  • Hip girdle pain
  • Neck pain
  • Functional impairment 1, 2
• Constitutional symptoms (common but not required):
  • Fever
  • Weight loss
  • Malaise 1

Laboratory Evaluation

Essential laboratory tests:

• Inflammatory markers:
  • Erythrocyte sedimentation rate (ESR) - typically >40 mm/hr
  • C-reactive protein (CRP)
  • Note: 20% of PMR cases may present with ESR <40 mm/hr (more common in men, with milder symptoms) 3

Required laboratory tests to exclude mimicking conditions:

• Rheumatoid factor (RF) and/or anti-cyclic citrullinated peptide antibodies (ACPA) to exclude rheumatoid arthritis
• Complete blood count
• Glucose
• Creatinine
• Liver function tests
• Bone profile (including calcium, alkaline phosphatase)
• Urinalysis 1

Additional recommended tests:

• Protein electrophoresis (to exclude paraproteinemia)
• Thyroid stimulating hormone (TSH) (to exclude thyroid disorders)
• Creatine kinase (CK) (to exclude myositis)
• Vitamin D level 1

Optional tests based on clinical presentation:

• Anti-nuclear antibodies (ANA)
• Anti-neutrophil cytoplasmic antibodies (ANCA)
• Tuberculosis tests 1

Imaging Studies

• Ultrasound: Can detect bilateral subdeltoid bursitis in 69% of PMR patients 2
• Additional imaging based on clinical suspicion to exclude other diagnoses:
  • Chest radiograph
  • Joint radiographs
  • MRI of affected areas 1

Exclusion of Mimicking Conditions

Must exclude:

1. Inflammatory conditions:

   • Giant cell arteritis (GCA) - evaluate for headache, jaw claudication, visual disturbances
   • Rheumatoid arthritis - particularly elderly-onset RA
   • Myositis

2. Non-inflammatory conditions:

   • Fibromyalgia
   • Osteoarthritis
   • Rotator cuff pathology
   • Adhesive capsulitis

3. Other causes:

   • Drug-induced myalgias
   • Endocrine disorders (thyroid, parathyroid)
   • Infections
   • Malignancy 1, 2, 4

Diagnostic Response to Treatment

• Rapid response to low-dose glucocorticoids (12.5-25 mg prednisone equivalent daily) is considered a diagnostic feature
• Clinical improvement should be noted within 2 weeks of starting treatment 1, 4

Specialist Referral Considerations

Consider rheumatology referral for:

• Atypical presentations (peripheral inflammatory arthritis, systemic symptoms, low inflammatory markers, age <60 years)
• High risk of treatment-related side effects
• Refractory disease or frequent relapses 1

Common Pitfalls in PMR Diagnosis

1. Delayed diagnosis: The average time from symptom onset to rheumatology referral is 13 months, leading to unnecessary testing and hospitalizations 5

2. Over-reliance on ESR: Up to 20% of PMR patients may present with ESR <40 mm/hr, particularly men who tend to have milder disease 3

3. Failure to consider GCA: PMR is associated with GCA in approximately 20% of cases, but subclinical large vessel vasculitis may be more common 6

4. Unnecessary imaging: Many patients undergo extensive imaging studies (abdominal CT, chest CT, cranial MRI) before diagnosis, which could be avoided with earlier consideration of PMR 5

By following this systematic diagnostic approach, clinicians can more efficiently diagnose PMR, avoid unnecessary testing, and initiate appropriate treatment to improve patient outcomes.