Plasma fibrinogen is an accurate marker of disease activity in patients with polymyalgia rheumatica

The overall aim of this study was to establish whether plasma fibrinogen was a superior biomarker of disease activity in active PMR than the standard biomarkers, ESR and CRP.

Sixty patients with PMR were divided into active (n = 25) or inactive (n = 35) disease groups based on symptoms, physician assessment and biomarkers ESR and CRP. Plasma fibrinogen was assayed. Groups underwent assessment at baseline and 6 weeks. Disease activity as per the PMR activity score (PMR-AS) was recorded at all visits. Receiver operator curves (ROCs), predictive values and likelihood ratios were calculated for all biomarkers.

Disease activity measures improved significantly in the active group between weeks 1 and 6 (P < 0.001). There was no significant difference between the activity scores at week 6 in the active group and the inactive group. Mean fibrinogen decreased from 5.2 to 3.5 g/l (normal <4 g/l) between weeks 1 and 6 in the active group. Mean ESR and CRP decreased from 59.6 to 24.3 mm/h (normal <30 mm/h) and 45.9 to 12.66 mg/l (normal <5 mg/l), respectively. Receiver operator curve analysis revealed fibrinogen to be more specific than either ESR or CRP for the detection of response to treatment in active PMR, with an overall sensitivity and specificity of 92% and 96%, respectively. Values above the upper limit of normal for fibrinogen, CRP and ESR were associated with likelihood ratios for active disease of 20.53, 2.9 and 2.8, respectively (P < 0.001).

Plasma fibrinogen is at least as useful as CRP and ESR for the diagnosis of active PMR and more specific for confirmation of response to treatment than either ESR or CRP.