Giant Cell Arteritis on 18F-FDG PET/CT: The Influence of Corticosteroid Therapy: A Case Report

Abstract

Background: Giant cell arteritis (GCA) is a granulomatous large-vessel vasculitis that typically affects patients over 50 years of age. It can lead to severe vascular complications, including irreversible blindness, highlighting the need for prompt diagnosis and immediate initiation                        of appropriate therapy. 18F-Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography (18F-FDG PET/CT) has emerged as a valuable tool for early diagnosis, but its sensitivity is influenced by prior corticosteroid treatment. Case Presentation: We report the case of a 73-year-old man who presented to the emergency department with acute-onset left eye blindness. Ophthalmological examination concluded ischemic optic neuropathy. The patient also reported persistent frontotemporal headaches and recent unintentional weight loss of 5 kg, accompanied by a significant biological inflammatory syndrome (ESR 92 mm/h, CRP 145 mg/L). GCA was strongly suspected, and high-dose systemic corticosteroid therapy was initiated urgently (intravenous boluses for three days, followed by oral prednisone at 1 mg/kg/day) due to the high risk of bilateral blindness. An 18F-FDG PET/CT scan performed five days after treatment initiation revealed moderate, linear, bilateral, and nearly symmetric hypermetabolism of the supra-aortic arterial trunks, particularly the common carotid and subclavian arteries, with maximum standardized uptake values (SUVmax) ranging from 2.3 to 3.4 (liver SUVmax 3.4). Based on the clinical, biological, and imaging findings, the diagnosis of GCA was established. Corticosteroid therapy was continued, leading to clinical improvement and normalization of inflammatory markers. Conclusion: This case illustrates that 18F-FDG PET/CT can retain diagnostic utility in GCA even after the initiation of corticosteroid therapy, provided the scan is performed within an optimal time window. However, the findings were borderline against formal 2022 ACR/EULAR classification criteria, highlighting that in equivocal cases, earlier imaging (ideally within 72 hours) may be necessary to obtain classification-level evidence. The case underscores the importance of interpreting PET/CT findings in the context of both treatment duration and the specific criteria being applied.