POS0100 DIAGNOSIS OF GIANT CELL ARTERITIS BY 18F-FDG PET/CT IN PATIENTS ON STEROID TREATMENT: IMPORTANCE OF DELAYED IMAGING
Authors: V. Aldasoro, V. Betech, S. Castañeda, M. Enguita, J. J. Rosales, M. J. Garcia Velloso
Journal: Annals of the Rheumatic Diseases (2024)

<h3>Background:</h3> Giant cell arteritis (GCA) is the most common type of vasculitis in caucasian patients over 50 years of age which can involves intracranial and extracranial vessels at the same time. Early diagnosis of GCA is essential for avoiding complications and irreversible sequelae. <sup>18</sup>F-FDG PET/CT (PET) has demonstrated to be a very useful image technique to evaluate extracranial arteries although by now, when it is performed in terms of high dose of steroids and further than 10 days on steroid treatment its usefulness decrease. <h3>Objectives:</h3> The aim of this study is to encourage the diagnostic value of PET despite the steroid dose and time on steroid treatment before PET performance in GCA patients. <h3>Methods:</h3> Consecutive diagnostic suspicious patients with GCA according to 2022 EULAR/ACR criteria as a reference standard were included. PET was performed at baseline and at 6 months. In patients with negative result at 60 minutes acquisition, delayed images were performed at 180 minutes. A total vascular score (TVS) was assessed at seven different vascular regions (thoracic aorta, abdominal aorta, subclavian arteries, axillary arteries, carotid arteries, iliac arteries, and femoral arteries), reported as negative (0) or positive, and further scored semi-quantitatively as 1 (minimal but not negligible FDG uptake), 2 (clearly increased FDG uptake), or 3 (very marked FDG uptake). PET/CT was considered positive if at least one arterial segment had a ≥ grade 2 hypermetabolism. For semi-quantitative analysis, volumes of interest (VOI) were drawn around the target arterial structures avoiding areas of atherosclerosis, and SUVmax at the liver and aortic wall to lumen ratio (corresponding to the TBR) were ascertained in both early and delayed acquisition, defining cut-offs for positivity of ≥ 1.34 [1,2]. <h3>Results:</h3> Twenty six patients were included with a median age of 70.5 (57-88) years. Baseline PET was positive in all but one: 18 patients at 60 min acquisition and 7 patients after delayed images at 180 min (Table 1 and Figure 1). The median dose of steroids at the time of the baseline PET was 45 mg/d (26.2-45) of prednisone - equivalent to a median exposure of 14 days (7-76.2). Delayed images were perfomed in more patients with more time on steroid treatment. At 6 months PET was performed on 22 patients, with positive results in 16, although metabolic activity had decreased in all cases. Delayed images were performed in 6 patients, with positive result in all cases, despite treatment with steroids and/or biological disease modifying antirheumatic drugs (bDMARD). Four patients died before the 6-month follow-up PET: 2 due to pneumonia, 1 due to abdominal aortic aneurysm rupture and another for unknown reasons. <h3>Conclusion:</h3> Early diagnosis of GCA is essential for avoiding complications and irreversible sequelae of this disease. A PET scan beyond 3-10 days after treatment initiation may be useful, especially in patients with a strong suspicion of GCA. In this context, in patients under long-term high dose steroid treatment, delayed imaging applying procedural recommendations for vascular quantification could be of great interest in clinical practice. In line with this GC dose seems to be less relevant than the time on steroid treatment. With this data we suggest to perform only one acquisition at 180 min in these kind of patients and in those with high suspicion of GCA and negative PET at 60 min. <h3>References:</h3> [1] Martínez-Rodríguez I, Del Castillo-Matos R, Quirce R, Banzo I, Jiménez-Bonilla J, Martínez-Amador N, Ibáñez-Bravo S, Lavado-Pérez C, Bravo-Ferrer Z, Carril JM. Aortic 18F-FDG PET/CT uptake pattern at 60 min (early) and 180 min (delayed) acquisition in a control population: a visual and semiquantitative comparative analysis. Nucl Med Commun. 2013 Sep;34(9):926-30. doi: 10.1097/MNM.0b013e32836370fb. [2] Martínez-Rodríguez I, Martínez-Amador N, Banzo I, Quirce R, Jiménez-Bonilla J, De Arcocha-Torres M, Ibáñez-Bravo S, Lavado-Pérez C, Bravo-Ferrer Z, Blanco R, González-Gay MA, Carril JM. Assessment of aortitis by semiquantitative analysis of 180-min 18F-FDG PET/CT acquisition images. Eur J Nucl Med Mol Imaging. 2014 Dec;41(12):2319-24. doi: 10.1007/s00259-014-2863-y. <h3>Acknowledgements:</h3> We thank the members of the Vascular Section of the Neurology Department and the Vascular Section of the Radiology Department at the HUN for their contributions to the ultrasound, CT and MRI image acquisition. <h3>Disclosure of Interests:</h3> <b>None declared.</b>