O16 Positron emission tomography - computed tomography: an important diagnostic tool in the giant cell arteritis fast track pathway

Abstract

Abstract Background/Aims Giant cell arteritis (GCA) is a systemic vasculitis affecting the temporal arteries and large vessels, including the aorta, in 25% of cases. Incidence of vertebral artery involvement is unknown likely owing to the reliance on conventional diagnostics including temporal artery biopsy (TAB) and temporal/axillary ultrasound which evade the vertebral arteries. These tests lose sensitivity soon after steroid initiation. Early specialist assessment and diagnostics, as part of a fast track pathway (FTP), can overcome this challenge. We present the first 12 months data from our FTP. To our knowledge this is the first GCA-FTP in the UK to utilise positron emission tomography - computed tomography (PET-CT) as an early diagnostic tool so we present a unique cohort of patients. Methods Cohort 1: 40 patients, diagnosed between 2015-2019, before FTP implementation. Time from steroid initiation to temporal artery ultrasound (TAUS) and TAB was recorded. Cohort 2: 35 patients referred after pathway implementation. 21 had a positive diagnosis. Time from steroid initiation to diagnostic test was recorded. Results Cohort 1: 26 (65%) patients had TAB; 3 (7.5%) had TAUS. The average time from starting steroid to investigation was 6 and 2 days respectively. Cohort 2: 17 (48%) had TAB, 30 (86%) had TAUS, 28 (80%) had PET-CT. In confirmed diagnoses, time from steroid initiation to investigations was 6.6 days, 1 day and 2.5 days respectively. In negative diagnoses time frames were 11.5, 1.5 and 2.3 days respectively. Table 1 shows sensitivity and specificity of these tests. Table 1. Sensitivity and specificity comparison between diagnostic tests Conclusion Combining TAUS and PET-CT allows for high diagnostic accuracy without the need for invasive biopsy. 24% of patients had negative or inconclusive ultrasound and/ or negative biopsy but confirmed vasculitis on PET-CT. 50% of this cohort had vertebral involvement only. PET-CT has an important role in detecting extracranial particularly vertebral arteritis, where biopsy and ultrasound are unreliable. Our pathway design with the inclusion of PET-CT, enables us to capture all patients with GCA and satisfy NHS England criteria for tocilizumab use in refractory GCA. Continued evaluation of PET-CT and its role in predicting vascular complications is required. Disclosure D.R. Ludwig: None. V. Morris: None. A. Shashidhara: None. S. Voo: None. R. Reshat: None.