From the Research
The diagnosis of polymyalgia rheumatica (PMR) relies on several laboratory tests, with elevated inflammatory markers being the most important, including erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), as well as serum amyloid A (SAA) in cases with normal ESR and CRP values. The primary tests for diagnosing PMR are ESR and CRP, with most PMR patients showing significant elevations (ESR typically >40 mm/hr and elevated CRP) 1. However, it is essential to note that some patients with PMR can have normal ESR and CRP values at the time of diagnosis, and in such cases, SAA can be used as an alternative inflammatory marker 1.
Some key laboratory tests used in the diagnosis of PMR include:
- Erythrocyte sedimentation rate (ESR)
- C-reactive protein (CRP)
- Serum amyloid A (SAA) in cases with normal ESR and CRP values
- Complete blood count (CBC) to reveal normocytic anemia and normal white blood cell counts
- Comprehensive metabolic panel to rule out other conditions and assess liver function
- Rheumatoid factor and anti-cyclic citrullinated peptide antibodies to distinguish PMR from rheumatoid arthritis
- Creatine kinase and aldolase levels to differentiate PMR from polymyositis
These laboratory findings, combined with clinical symptoms like bilateral shoulder and hip pain, morning stiffness, and response to low-dose corticosteroids, help establish the diagnosis of PMR, as there is no single definitive test for the condition 2, 3. Ultrasonography can also be used to demonstrate bursitis in patients with normal ESR and CRP values, supporting the diagnosis of PMR 1.
In cases where giant cell arteritis is suspected, additional tests may be necessary to confirm the diagnosis. The European League Against Rheumatism (EULAR) response criteria for PMR comprise a core set of markers for monitoring therapeutic responses in PMR, including ESR or CRP, the visual analogue scale of patient's pain, and physician's global assessment, as well as morning stiffness and the ability to elevate the upper limbs 2.
Overall, the diagnosis of PMR requires a combination of clinical evaluation, laboratory tests, and imaging studies to establish the diagnosis and rule out other conditions. The most recent and highest quality study 1 suggests that SAA can be a useful marker in cases with normal ESR and CRP values, highlighting the importance of considering alternative inflammatory markers in the diagnosis of PMR.