A PROSPECTIVE STUDY EVALUATING A PRE-TEST PROBABILITY SCORE IN THE DIAGNOSIS OF GIANT CELL ARTERITIS

C. Kirby, R. Flood, S. Norton, J. Galloway, R. Mullan, G. Murphy, D. KaneTallaght University Hospital, Rheumatology, Dublin, Ireland King’s College London, Centre for Rheumatic Diseases, London, United Kingdom King’s College Hospital, Rheumatology, London, United Kingdom Cork University Hospital, Rheumatology, Cork, Ireland  Background Temporal Artery Ultrasound (TAUS) has been increasingly used in recent years to diagnose Giant Cell Arteritis (GCA) but has shown widely disparate results in studies to date [1-3]. A Pre-Test Probability Score (PTPS) has been developed to standardise the estimation of clinical probability of having GCA which, to date, has been validated in only one prospective study [4]. Objectives To evaluate the diagnostic utility of the PTPS and to investigate whether its use can improve the sensitivity of US. Methods We performed a prospective multicentre study of all new referrals to our Rapid Access GCA clinic over 18 months. US of all branches of the Superficial Temporal (STA) and Axillary Arteries (AA) was performed using a GE P9 device. Sonographic abnormalities considered indicative of vasculitis included the halo sign and non-compressible arteries with a thickened intima-media complex [5]. The PTPS (scale 0-30) incorporates a number of variables to quantify the likelihood of having a diagnosis of GCA (Table 1) [4]. We compared results to a clinical diagnosis of GCA at 6 months, verified by 2 rheumatologists. We performed Chi-Square tests with ROC analyses and logistic regression to determine the diagnostic performance of the PTPS, US and of both tools combined. Image/graph:Table 1. The Pre-Test Probability Score of having a diagnosis of GCA incorporates patient demographics, symptoms, examination findings, laboratory results and relevant false negatives, with a maximum score 30. Y = Yes (present), N = No (absent). Results 72/149 patients had a diagnosis of GCA with a mean age of 73.3 years of whom 58% were males. The PTPS AUC for a diagnosis of GCA was 0.807 (95% CI 0.736-0.875). At scores <10, the PTPS correctly refuted the diagnosis in 91.67%, with lower scores having even higher sensitivities. At scores >13, it correctly identifies the diagnosis in 93.51%, with higher scores having even higher specificities. The TAUS AUC for a diagnosis of GCA was 0.865 (95% CI 0.810- 0.920). A model which combines both PTPS and TAUS out-performs both individual tools with an AUC 0.912 and is illustrated in Figure 1. In the case of positive US, a PTPS ≥6 infers a >60% likelihood of having GCA. In cases of negative US, a PTPS ≤12 infers a <20% likelihood of having GCA. Image/graph:Figure 1. Probability of having a diagnosis of GCA at various PTPS in US-positive (above, blue) and US-negative (below, green) patients, with confidence intervals. Conclusion Our study demonstrates a strong correlation between baseline PTPS and a clinical diagnosis of GCA at 6 months, in a large prospective cohort. Although US is superior to PTPS for diagnosis of GCA, a model which combines both tools achieves a sensitivity of 91%, higher than that for US alone. This model can form the basis of an algorithm to guide early corticosteroid use in cases of suspected GCA. References Schmidt WA, Kraft HE, Völker L, Vorpahl K, Gromnica-Ihle EJ. Colour Doppler sonography to diagnose temporal arteritis. Lancet (London, England). 1995;345(8953):866. Bilyk JR, Murchison AP, Leiby BT, Sergott RC, Eagle RC, Needleman L, et al. The Utility of Color Duplex Ultrasonography in the Diagnosis of Giant Cell Arteritis: A Prospective, Masked Study. (An American Ophthalmological Society Thesis). Transactions of the American Ophthalmological Society. 2017;115:T9. Luqmani R, Lee E, Singh S, Gillett M, Schmidt WA, Bradburn M, et al. The Role of Ultrasound Compared to Biopsy of Temporal Arteries in the Diagnosis and Treatment of Giant Cell Arteritis (TABUL): a diagnostic accuracy and cost-effectiveness study. Health technology assessment (Winchester, England). 2016;20(90):1-238. Sebastian A, Tomelleri A, Kayani A, Prieto-Pena D, Ranasinghe C, Dasgupta B. Probability-based algorithm using ultrasound and additional tests for suspected GCA in a fast-track clinic. RMD open. 2020;6[3]. Schäfer VS, Juche A, Ramiro S, Krause A, Schmidt WA. Ultrasound cut-off values for intima-media thickness of temporal, facial and axillary arteries in giant cell arteritis. Rheumatology (Oxford, England). 2017;56(9):1479-83. Acknowledgements: NIL. Disclosure of Interests None Declared. Keywords: Diagnostic tests, Vasculitis, Ultrasound DOI: 10.1136/annrheumdis-2023-eular.5693Citation: , volume 82, supplement 1, year 2023, page 632Session: Vasculitis - large vessel vasculitis (Poster View)