P196 The changing role of biopsy and imaging in the diagnosis of giant cell arteritis prior to tocilizumab treatment

Abstract

Abstract Background/Aims Vasculitis has always relied on pattern recognition, biopsy and imaging to secure a diagnosis. Historically, giant cell arteritis diagnosis has relied too heavily on pattern recognition without scrutiny. The current guidelines recommend securing a diagnosis by either temporal artery biopsy (TAB) or imaging. Ultrasound (US) has been given parity with biopsy in European guidelines for cranial giant cell arteritis (cGCA) although in the USA experience is more limited. Large vessel vasculitis (LVV) may not present with cranial symptoms and is diagnosed by axillary US, MRA or preferably PET. The Clyde GCA Fast Track US Pathway was introduced in 2018 and follows EULAR imaging guidelines. In a health board with access to all diagnostic modalities, how is GCA being diagnosed in patients treated with tocilizumab? How is this changing over time? Methods 46 patients commenced on tocilizumab for GCA since 2017 had their diagnoses examined. Electronic records and US data were used to categorise diagnosis as a result of biopsy, MRA, PET, ultrasound or clinical diagnosis alone. Clinical diagnoses with neither imaging nor biopsy were reviewed in more depth. Results There were 37 women and 9 men; 33 cranial GCA and 13 LVV; 9 presenting with a relapsing pattern of disease and 37 with new presentations. Age range 59-91 (mean of 73 years). Only 3 of 46 patients had no additional proof of diagnosis. Diagnosis was secured by biopsy in 16 and imaging in 27 (14 US and 13 PET). Conclusion By 2022, cGCA was equally likely to be diagnosed by US as biopsy. The fast track US service provided support for patients, referrers and surgeons to determine if biopsy was needed to secure a diagnosis. Biopsy was most valuable in delayed presentations or if clinical suspicion was high but US negative. PET is the most useful imaging technique for diagnosing LVV; US of axillary arteries was only positive in a few cases and unable to cover the differential diagnosis. MRA was informative but not diagnostic. All GCA diagnoses should be based on good evidence to warrant the potential toxicity of steroids, tocilizumab and any future treatments for relapsing disease. Disclosure L.M.M. Hutton: None.