THU0443 A probability score from a fast track clinic to aid the management of suspected giant cell arteritis

Abstract

BackgroundDiagnosis of Giant Cell Arteritis(GCA) is difficult since its manifestations are protean1. Under-diagnosis is associated with ischaemic complications whereas over diagnosis is associated with inappropriate glucocorticoids (GC)2.GCA is diagnosed by different specialties, including family physicians, who would benefit from a clinical prediction score.A fast track pathway also requires clinical triage in terms of probability of disease. We evaluated all referred patients (08/16–08/17) to develop a pre-test probability score(PTBS) to support a diagnostic pathway and decision-making.MethodsThe PTBS was generated from long standing clinical experience. Information collected at initial assessment was given varying positive weightage. This included baseline demographics (age-gender), symptomatology at presentation(onset, headache and scalp tenderness, ischaemic symptoms, constitutional symptoms, polymyalgia),C-Reactive protein(CRP) and examination findings(ischaemic ophthalmic complications, temporal artery abnormalities, extra-cranial abnormalities, cranial nerve palsies). Negative weightage was given for competing diagnoses (infection, cancer, head and neck pathology, systemic rheumatological diseases). The PTBS was compared with the final diagnosis as GCA or non-GCA 6 months after the initial assessment. Analysis was performed in Stata SE, version 13.1.Results122 PTBS were collected of which CRP was missing in 1 case which was excluded from the analysis.23 had a final diagnosis of GCA at 6 months follow up. The rest consist our control group(99 patients). The area under the ROC curve for the 121 cases was 0.953 (figure 1). Using the bootstrap method gave an estimated area under the ROC curve (95% confidence interval) of 0.953 (0.911, 0.994). At the point of inflection, corresponding to a cut point of 9.5, sensitivity was 95.7%, and specificity was 86.7%;the likelihood ratio for a positive test was 7.2 and the likelihood ratio for a negative test, 0.050. At this cut point, 88.4% cases were correctly classified.ConclusionsThis single centre retrospective study suggests that PTBS is a useful standardised assessment tool for rating pre-test probability for GCA with high levels of sensitivity and specificity. PTBS may reduce variation in clinical assessment and aid decision making.A patient with low probability score(<9.5) can be managed with colour doppler ultrasound examination(US) which if negative will exclude the disease and the clinician can reassure patient.A patient with high PTBS and positive US can safely have the diagnosis confirmed and treated with GC. With intermediate scores, conflicting PTBS and US findings, equivocal US, additional investigations including TA biopsy and/or other imaging scans may be needed. Our results need validation in a prospective study and in internal and external validation cohorts. PTBS has the potential for forming the basis for education programme for the correct and early diagnosis of GCA and limit inappropriate GC in non GCA mimics.References[1] Murchison AP, et al. Vali...

Probability-based algorithm using ultrasound and additional tests for suspected GCA in a fast-track clinic

“…We are pleased our current definitions fit well with the cut-off of 9.5, dividing LRC from IRC and HRC (ie, LRC is <9) reported from the original study. 20 The test performance of US in GCA was considerably enhanced with this Bayesian probability-based approach, as sensitivity, specificity, PPV and NPV of US overall and in all categories were much higher than previously reported (sensitivity in LC was undefined since there were no false negatives). 29 We feel such a pretest Bayesian approach markedly augments the diagnostic performance of a test such as US and forms the rational basis for planning AT based on progress through the algorithm.…”

“…It also validates our cut-offs for the three probability groups categorised based on probability scores obtained overall for the entire 2-year referrals. 20 Any score above Q3 (>75th percentile, ie, >12) was HRC, between Q2 and Q3 (50th-75th percentile, ie, 9-12) was IRC and less than Q2 (<50th percentile, ie, <9) was LRC. We have considered in future of adding a very low category below Q1 (<25th percentile, ie, score <7) but this is not the subject of the current study.…”

“…4 We have previously reported a pretest probability score (PTPS) that shows promise to stratify patients into low-risk category (LRC), intermediate-risk category (IRC) and high-risk category (HRC) when first seen. 20 Herein, we analyse our experience over 2 years (2018-2019) of pretest probability triage (with a primary US test and additional tests (AT) to follow), with the objective of describing a probability-based secure diagnostic algorithm that works in clinical practice. The main objective was to develop a joined-up, end-to-end, fast-track confirmatory/exclusionary, algorithmic process based on a probability score triage to drive subsequent investigations with US and any appropriate AT as required.…”

Halo score (temporal artery, its branches and axillary artery) as a diagnostic, prognostic and disease monitoring tool for Giant Cell Arteritis (GCA)

“…In patients with a low clinical probability and a negative imaging result, the diagnosis of GCA can be considered unlikely, and the patient reassured [18]. There is also a report from Southend suggesting that the 'pre-test GCA Probability Score' may be a useful tool for rating the pre-test probability of GCA, stratifying patients into 'low' or 'not-low' probability groups [28]. This score may also reflect clinical severity and extent of disease.…”

Clinical Applicability of Ultrasound in Systemic Large Vessel Vasculitides

“…It is hoped that this flow chart will provide a suitable algorithm for clinicians using ultrasound in patients in whom GCA is suspected. In addition, Laskou et al have recently developed a possibly implementable GCA probability–scoring tool that can calculate the likelihood of GCA . If proven valid, such a scoring system can provide additional reassurances in the assessment of GCA.…”