Digital [18F]FDG PET/CT as first-line diagnostic modality for cranial giant cell arteritis.

PURPOSE: Diagnosis of giant cell arteritis (GCA) is challenging and relies mainly on temporal artery biopsy and/or Doppler ultrasound (DUS). Although [18F]FDG PET/CT is the test of choice suspected large vessel (LV)-GCA, its use in cranial artery GCA (C-GCA) detection was previously limited. Digital PET/CT devices have improved resolution and sensitivity for smaller lesions. This international prospective cross-sectional comparative study investigates the diagnostic accuracy of digital PET/CT and DUS in patients with suspected GCA. METHODS: Patients aged ≥ 50 years with suspected GCA based on classical symptoms and inflammatory markers were enrolled. Exclusion criteria included corticosteroid therapy for > 3 days prior to PET/CT or prior history of vasculitis. PET/CT scans were interpreted independently by two blinded readers using standardized visual grading scales; in case of disagreement, a third blinded reader adjudicated. DUS of the temporal and axillary arteries was performed as standard of care. Temporal artery biopsy was performed at the treating physician's discretion. Final clinical diagnosis at 6 months served as reference standard. RESULTS: Of 92 enrolled subjects, 8 were excluded as they did not undergo DUS. Eighty-four subjects (mean age: 72 years; mean CRP: 70.7 mg/L) were included in the analysis with mean follow-up of 27 months (range 6-74). GCA was diagnosed in 44/84 patients. PET/CT sensitivity increased from 50.0% (95%CI: 34.6-65.4%) to 86.4% (95%CI: 72.7-94.8%) when incorporating C-GCA assessment, with specificity at 100.0% (95%CI: 91.2-100.0%). DUS demonstrated sensitivity 68.2% (95%CI: 52.4-81.4%) and specificity 92.5% (95%CI: 79.6-98.4%). CONCLUSION: Digital [18F]FDG PET/CT demonstrates high diagnostic accuracy for the diagnosis of C-GCA, supporting its potential role as a first-line modality in the evaluation of suspected GCA. TRIAL REGISTRATION NUMBER: NCT05000138. Trial registration date: 2021-08-03 (submission), 2022-06-10 (study start).