Orbital Gallium-67 Scintigraphy in Graves' Ophthalmopathy: A Disease Activity Parameter that Predicts the Therapeutic Response to Immunosuppressive Treatment

In this study, orbital gallium-67 citrate (⁶⁷Ga) scintigraphy was evaluated as a disease activity parameter that can predict the therapeutic response to immunosuppressive treatment in Graves' ophthalmopathy. Orbital scintigraphic analysis was performed on 32 patients demonstrating moderate to severe Graves' ophthalmopathy. Single-photon emission computed tomography (SPECT) images were obtained 48 hours after intravenous injection of 148 MBq of radioactive ⁶⁷Ga complex, and orbit/occipital (O/Occ) ratios were calculated to correct the background activity. Intravenous methylprednisolone was given as immunosuppressive treatment to 24 patients (group 1) and 8 patients were followed up without any treatment and evaluated as controls (group 2). Orbital ⁶⁷Ga scintigraphy was repeated in all patients after 6 months to analyze the changes in clinical findings and orbital ⁶⁷Ga accumulation. In Group 1, the mean ± standard deviation (SD) ⁶⁷Ga O/Occ ratio of responders(2.23 ± 0.2, 16 cases) was statistically different from nonresponders (1.49 ± 0.1, 8 cases, p < 0.001). Additionally, the corticosteroid treatment provided a significant decrease in orbital ⁶⁷Ga accumulation in responders(p < 0.001), however, it did not change statistically in nonresponders (p:0.13). In group 2, the patients did not demonstrate clinical improvement and orbital ⁶⁷Ga uptake did not change after the follow-up period (p:0.81). The receiver-operator-characteristic curve showed that the best threshold for discriminating responder and nonresponder groups was 1.70 (sensitivity, 94%; specificity, 88%). This study demonstrated that orbital ⁶⁷Ga scintigraphy may be a useful imaging technique in predicting the therapeutic response to immunosuppressive treatment in Graves' ophthalmopathy.