Aim To assess the usefulness of ¹⁸F-fluorodeoxyglucose positron emission tomography (¹⁸F-FDG PET/CT) and the predictive factors for the diagnosis of sarcoidosis in patients with uveitis who have normal thoracic tomography.

Methods We retrospectively reviewed 67 consecutive patients with uveitis of unknown aetiology or a suspected sarcoidosis. All patients with normal thoracic tomography underwent an ¹⁸F-FDG PET/CT, which was blindly reinterpreted. We then assessed the proportion of positive ¹⁸F-FDG PET/CT and the impact on the final aetiology, using Abad’s criteria for the diagnosis of intraocular sarcoidosis.

Results 19 of the 67 patients (28.4%) had mediastinal hypermetabolic foci on their ¹⁸F-FDG PET/CT consistent with sarcoidosis. It identified a biopsy site in two cases, which were consistent with sarcoidosis. At the end of the study, six patients (10%) had a proven sarcoidosis, six patients (9%) were considered as having a presumed sarcoidosis and 18 patients (26.9%) as having indeterminate sarcoidosis. ¹⁸F-FDG PET/CT enabled the diagnosis of presumed sarcoidosis in these six patients. An older age at diagnosis (p=0.004) and the presence of synechiae (p=0.02) were significantly related to an abnormal ¹⁸F-FDG PET/CT, with a trend for an elevated ACE (p=0.0993). We established a nomogram to estimate the probability of having positive findings on the ¹⁸F-FDG PET/CT according to different predictive factors.

Conclusion ¹⁸F-FDG PET/CT enabled the diagnosis of intraocular sarcoidosis even in patients with a normal CT scan. Older age at diagnosis, presence of synechiae and elevated ACE are associated with positive findings on ¹⁸F-FDG PET/CT consistent with sarcoidosis.