ESR as a Preferred Marker for Polymyalgia Rheumatica
ESR is traditionally preferred over CRP as a marker for polymyalgia rheumatica (PMR) because elevated ESR (>40 mm/1st hour) has been identified as an independent risk factor for relapse and prolonged therapy, making it more valuable for long-term disease monitoring. 1
Diagnostic Value of ESR vs CRP in PMR
ESR is specifically mentioned in PMR guidelines as a key laboratory marker, with high ESR (>40 mm/1st hour) being associated with higher relapse rates and need for prolonged therapy 1
Both ESR and CRP are typically elevated in PMR, with CRP being more sensitive (only 1% of PMR patients have normal CRP at diagnosis compared to 6% with normal ESR) 2
The 2015 EULAR/ACR guidelines recommend measuring both ESR and CRP as part of the basic laboratory dataset for PMR diagnosis and monitoring 1
Why ESR May Be Preferred Over CRP
Physiological Differences
ESR is an indirect measure of fibrinogen which has a longer half-life than CRP, making it more suitable for monitoring chronic inflammatory conditions like PMR 3
CRP responds more rapidly to changes in inflammation, making it better for monitoring acute inflammatory responses and immediate treatment effects 3
Prognostic Value
ESR >40 mm/1st hour at diagnosis has been identified as an independent predictor of relapse with a relative risk approximately twice that of elevated CRP (relative risk 4.9 vs 2.1) 2
Multiple studies have shown that high baseline ESR is associated with higher relapse rates and/or prolonged therapy requirements in PMR patients 1
Clinical Application
In PMR management algorithms, ESR is specifically highlighted when determining initial glucocorticoid dosing, with high ESR (>40 mm/1st hour) being a factor that might favor higher initial doses 1
While CRP is more sensitive for current disease activity, ESR appears to have superior predictive value for the long-term disease course 2
Complementary Role of Both Markers
During disease flares or relapses, ESR may sometimes be normal while CRP remains elevated, suggesting that both markers provide complementary information 2
In a study of PMR relapses, 25 episodes occurred with normal ESR, but CRP was elevated in 62% of these episodes, indicating CRP's value in detecting active inflammation when ESR is normal 2
For comprehensive disease monitoring, the EULAR response criteria for PMR include either ESR or CRP as part of the core set of assessment measures 4
Special Considerations
In cases where clinical symptoms persist despite normalization of both ESR and CRP after starting treatment, other inflammatory markers like serum amyloid A (SAA) might be considered as additional therapeutic markers 5
Some patients (approximately 6%) may present with normal ESR at diagnosis but still have elevated CRP, highlighting the importance of measuring both markers 2
PMR with normal inflammatory markers is considered an atypical presentation that warrants specialist referral according to current guidelines 1