Background/Purpose: Every effort should be made to confirm a suspected diagnosis of giant cell arteritis (GCA). According to the 2018 update of the EULAR recommendations for the management of large vessel vasculitis, objective confirmation of the presence of vasculitis should always be obtained by histology (temporal artery biopsy [TAB]) or imaging, with color Doppler ultrasound (CDUS) of the temporal arteries being the most commonly used imaging method. However, in clinical practice, it is not uncommon to encounter patients with negative cranial studies, and this subgroup, remains the most challenging to diagnosis. The present study aimed to investigate the diagnostic performance of ¹⁸F-FDG PET-CT for assessing large vessel involvement in patients with suspected GCA and a negative TAB.

Methods: We retrospectively reviewed our hospital databases to identify all patients with suspected GCA and a negative TAB who underwent an ¹⁸F-FDG PET-CT in an attempt to confirm the diagnosis. The gold standard for GCA diagnosis was clinical confirmation after a follow-up period of at least 12 months.

Results: One hundred and twenty-seven patients were included. After a detailed review of the medical records, 73 patients were finally diagnosed has having GCA. Three of the remaining 54 subjects were diagnosed with other types of vasculitis, and 51 had other diagnoses. Among the 73 patients diagnosed with GCA, ¹⁸F-FDG PET-CT was considered positive in 61 cases (83.5%). Nine of the 12 GCA patients with negative PET-CT had undergone previous glucocorticoid treatment. Of the 54 patients without ACG, FDG-PET was considered positive in only 8 (14.8%) (1 case of Erdheim-Chester disease, 3 IgG4-related disease, 1 case of sarcoidosis, and 3 clinically isolated aortitis). Overall, the diagnostic performance of ¹⁸F-FDG PET-CT in assessing large vessel involvement in patients with suspected GCA and negative TAB yielded 83.5% sensitivity, 85.1% specificity, and a diagnostic accuracy of 84% with an area under the ROC curve of 0.844 (95% CI:0.752 to 0.936).

Conclusion: Our study confirms the usefulness of ¹⁸F-FDG PET-CT when the GCA diagnosis is uncertain following a negative TAB result, by demonstrating the presence of large vessel vasculitis.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/diagnostic-yield-of-18f-fdg-pet-ct-for-large-vessel-involvement-in-patients-with-suspected-giant-cell-arteritis-and-negative-temporal-artery-biopsy/