F-18 Fluorodeoxyglucose PET/CT as a Diagnostic Tool in Orbital Inflammatory Disorders

Abstract Background: In the last decade, FDG-PET/CT has become routine practice in the management of lymphoma or autoimmune diseases. In the current study, we aimed to assess the usefulness of FDG-PET/CT as a potential diagnostic tool for detecting underlying systemic diseases (SD) in patients with orbital inflammatory disorders (OID).Methods: All consecutive patients managed for new-onset OID between 2011 and 2018 in a tertiary referral center for OID, who underwent FDG-PET/CT as part as the etiological diagnostic workup were enrolled. PET-FDG/CT scans were reviewed blindly and were considered as positive for SD detection if they showed lymphadenopathy and/or other visceral lesions with an uptake above blood pool background. We used the standard diagnostic workup (performed in all patients at presentation) as relevant comparator. To quantify the incremental value of FDG-PET/CT over the standard diagnostic workup, the Net Reclassification Index (NRI) and Integrated Discrimination Index (IDI) were used. The final diagnosis was based on international criteria for autoimmune diseases, or histological confirmation for lymphoma, xanthogranuloma, crystal storing histiocytosis (CSH), or idiopathic orbital inflammation syndrome (IOIS). Results: Among the 22 patients enrolled, 14 (63%) had underlying SD (granulomatosis with polyangiitis (GPA), n=1; IgG4-related disease (IgG4-RD), n=5; CSH, n=1; adult onset asthma and periocular xanthogranuloma (AAPOX), n=3; lymphoma, n=4) while the remaining 8 (37%) patients were diagnosed with IOIS. Eleven (50%) patients had a positive FDG-PET/CT. After clinicobiological evaluation, FDG-PET/CT correctly reclassified 29% of patients with SD (p=0.04) and 13% with IOIS (p=0.3), corresponding to an elevated NRI of 0.41±0.17 (p=0.03). The IDI test used to evaluate the improvement of FDG-PET/CT for SD detection was 0.38±0.08 (p<0.001). After FDG-PET/CT, probability changes for SD and IOIS were measured at 0.14 and -0.24, respectively (relative gain of 3.04 for IDI). FDG-PET/CT successfully detected asymptomatic lesions in all patients with a final diagnosis of lymphoma. Conclusion: FDG-PET/CT enabled accurate reclassification of more than one quarter of patients with SD, suggesting its potential value for detecting SD (especially extraorbital lymphoma).