Initial Investigations for Polymyalgia Rheumatica (PMR)
The initial workup for suspected polymyalgia rheumatica should include a comprehensive laboratory assessment with inflammatory markers, autoantibody testing, and basic metabolic parameters to exclude mimicking conditions. 1
Core Laboratory Tests
- Inflammatory markers: Erythrocyte sedimentation rate (ESR) and/or C-reactive protein (CRP) are essential as they are typically elevated in >90% of PMR cases 1, 2
- Complete blood count to assess for anemia and exclude other causes of inflammation 1
- Rheumatoid factor and/or anti-cyclic citrullinated peptide antibodies (ACPA) to exclude rheumatoid arthritis 1, 3
- 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, 4
- Vitamin D level to establish a baseline before potential glucocorticoid therapy 1
Extended Testing Based on Clinical Presentation
- Serological tests including 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
- Imaging studies such as chest radiographs to exclude other diagnoses like malignancy 1
Special Considerations for Laboratory Testing
- ESR is typically elevated (>40 mm/1st hour) in most PMR cases, but approximately 20% of patients may present with an ESR <40 mm/h 5, 6
- Patients with low ESR PMR tend to be younger, more frequently male, and have less systemic symptoms (fever, weight loss) 6
- Both ESR and CRP should be measured, as ESR has been shown to be a better indicator of clinical disease activity in most cases 7
- Normal inflammatory markers do not exclude the diagnosis of PMR if clinical presentation is typical 5
Diagnostic Approach Algorithm
- Assess for clinical features: bilateral shoulder pain, morning stiffness, functional impairment, and age >50 years 1, 2
- Order core laboratory tests as listed above 1
- Consider a therapeutic trial with low-dose glucocorticoids (12.5-25 mg prednisone equivalent) as a diagnostic tool - prompt response supports diagnosis 1, 3
- Exclude mimicking conditions: inflammatory arthritis, endocrine disorders, infections, malignancies 1, 4
When to Consider Specialist Referral
- Atypical presentations including peripheral inflammatory arthritis 3
- Systemic symptoms suggesting alternative diagnoses 3
- Age <60 years 3
- High risk of treatment-related side effects 3
- Normal inflammatory markers despite typical clinical presentation 5
Remember that no single test is pathognomonic for PMR; diagnosis remains primarily clinical, supported by laboratory evidence of inflammation and exclusion of other disorders 1.