Background Determination of disease activity in polymyalgia rheumatica (PMR) is challenging due to the subjective nature of symptoms and prevalence of concurrent musculoskeletal complaints in an elderly population. Traditionally the non specific inflammatory markers ESR and CRP have been used to guide therapeutic decisions. CRP and ESR may be normal in up to 20% of patients with PMR at the time of diagnosis. Normal ESR or CRP values have been observed in 27% and 14% of relapses, respectively. Any biomarker than assists physicians in more accurately determining patients disease status and therefore enabling accurate adjustment of glucocorticoid dose would be welcomed. Previously we have demonstrated the enhanced specificity of plasma fibrinogen over both ESR and CRP for the detection of response to treatment in patients with active PMR.
Objectives To prospectively evaluate the utility of the biomarkers ESR, CRP and Fibrinogen for identifying different disease states in patients with known PMR.
Methods Patients with PMR (as per Jones-Hazleman criteria) were divided into high/medium (Group 1) or low (Group 2) disease activity as per the Polymyalgia Rheumatica Activity Score (PMR-AS). A PMR-AS >7 indicates medium/high disease activity with a PMR-AS <7 indicating low disease activity1. Plasma fibrinogen, CRP and ESR were also assayed. An ESR value of 30mm/hr (lab normal <20mm/hr) and CRP of 8mg/L (lab normal <5mg/l) were considered the upper limit for detection of low disease activity. The upper limit of the lab normal for Fibrinogen (4g/L) was used. Sensitivity, specificity, positive predictive values and likelihood ratios were calculated for all biomarkers.
Results Data was available from 120 patient visits. Demographic data was similar in both groups. Mean age was 71.8 years. All patients were receiving glucocorticoids with a median steroid dose of 10mg in Group 1 and 5mg in Group 2.There were significant differences in steroid dose between the two groups (p<.001). 70 patients were defined as having low disease activity as per the PMR-AS. Of these 6/70 had an elevated plasma fibrinogen with 14/70 having an ESR >30mm/hr and 18/70 a CRP >8mg/L. The specificity, sensitivity, positive predictive values and likelihood ratios for the different biomarkers as calculated for all 120 patient visits are shown in the table below.
Whilst CRP was the most sensitive biomarker, plasma fibrinogen was more specific than either ESR or CRP for differentiating between low disease activity and moderate/high disease activity in PMR. It also demonstrated a superior positive predictive value and likelihood ratio than ESR and CRP for identifying patients with moderate/high disease activity.
Conclusions Elevated Plasma fibrinogen more accurately indicates that patients are in a persistent moderate or high disease activity state than elevation of ESR or CRP. Measurement of fibrinogen as an adjunct to ESR and CRP in patients with PMR may therefore help treating physicians more accurately identify patients’ disease status and guide decisions with regards glucocorticoid dosage.
A disease activity score for polymyalgia rheumatica. Leeb BF, Bird HA. Ann Rheum Dis. 2004 Oct;63(10):1279-83.
Disclosure of Interest None Declared
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