Background Color duplex ultrasonography (CDU) is recommended as first line of imaging in patients suspected for cranial GCA [1]. However, extra-cranial involvement without temporal artery involvement is found in up to 40% of GCA patients [2]. CDU is very suitable to also assess extra-cranial artery inflammation, of which the axillary artery is relatively easy to assess. However, data on the value of CDU in extra-cranial GCA is limited [3].

Objectives We aimed to (1) evaluate the performance of axillary artery CDU in patients with extra-cranial GCA by comparing CDU findings with [18F]-FDG PET/CT findings. Furthermore, to (2) compare the sensitivity and specificity of adding assessment of axillary arteries to temporal artery CDU, over temporal artery CDU only.

Methods Consecutive patients suspected of GCA who underwent CDU examination of the temporal and axillary arties between 2013 and 2017 were retrospectively included. The presence of a halo or occlusion was considered a positive CDU finding for GCA. In patients with PET-proven extra-cranial GCA, an axillary FDG uptake higher than liver uptake was considered positive. The reference was the clinical diagnosis (GCA or not) after 6 months.

Results Of the 113 included patients, GCA was diagnosed in 41 and excluded in 72 patients at 6 months reference. PET-proven extra-cranial involvement was present in 20/41 GCA patients, of which 13 showed axillary involvement. An axillary halo was found in 8/13 of these patients, consistent with an increased FDG uptake. In 5/13, axillary involvement on PET was missed with axillary CDU (1/5 on steroids). However, in 4/5 of these an halo was found in the temporal arteries. Additionally, 6/20 patients with extra-cranial involvement did not show axillary involvement on both CDU and PET. All 6 had isolated involvement of a single artery on PET (2 aorta; 4 vertebral). CDU found a temporal halo in 3 of them. Overall, CDU of only the temporal arteries resulted in a sensitivity of 52% (95CI 35-67) and a specificity of 93% (95CI 84-97) for the reference diagnosis at 6 months. Adding CDU results of axillary arteries improved sensitivity to 71% (95CI 55-84), while specificity did not change. Although not systematically assessed, adding CDU assessment of the subclavian arteries improved sensitivity to 76% (95CI 59 – 87).

Conclusion In case of an axillary halo no further FDG PET/CT scanning is required to diagnose extra-cranial GCA. In this study, investigation of both temporal and axillary arteries substantially increased the diagnostic performance of CDU. Furthermore, CDU and FDG PET arterial involvement is not always congruent, and occasionally arterial involvement is restricted to vessels not systematically assessed with CDU in our center. In patients in whom the axillary CDU is negative, a targeted CDU of selected vessels (e.g. subclavian, carotid or vertebral), or an FDG PET/CT is mandatory.

References [1] Dejaco C, Ramiro S, Duftner C, et al. EULAR recommendations for the use of imaging in large vessel vasculitis in clinical practice. Ann Rheum Dis. 2018;77(5):636-643.

[2] Schmidt WA, Seifert A, Gromnica-Ihle E, et al. Ultrasound of proximal upper extremity arteries to increase the diagnostic yield in large-vessel giant cell arteritis. Rheumatology (Oxford). 2008;47(1):96-101.

[3] Duftner C, Dejaco C, Sepriano A, et al. Imaging in diagnosis, outcome prediction and monitoring of large vessel vasculitis: A systematic literature review and meta-analysis informing the EULAR recommendations. RMD Open. 2018;4(1):e000612-2017-000612. eCollection 2018.

Disclosure of Interests Hilde Hop: None declared, Douwe J Mulder Grant/research support from: My University has received research grants for my research from: Boehringer Ingelheim and Actelion, Speakers bureau: My University has received speakers fee from: Sanofi, Maria Sandovici: None declared, Andor Glaudemans: None declared, Arie Van Roon: None declared, Riemer Slart: None declared, Elisabeth Brouwer Speakers bureau: Dr. Brouwer as an employee of the UMCG received speaker fees and consulting fees from Roche which were paid to the UMCG