Retrobulbar 99mTc-Diethylenetriamine-Pentaacetic-Acid Uptake May Predict the Effectiveness of Immunosuppressive Therapy in Graves' Ophthalmopathy

Background: In Graves' ophthalmopathy (GO), only patients with immunologically active disease respond to immunosuppressive therapy. Previous studies and theoretical considerations suggest that elevated orbital 99m Tc-diethylenetriamine-pentaacetic-acid (DTPA) single photon emission computed tomography (SPECT) reflects inflammatory disease activity. We studied whether corticosteroid treatment causes a substantial decrease in DTPA uptake in GO, a result consistent with successful immunosuppressive treatment of GO and referred to as a favorable treatment outcome. Methods: One hundred fourteen orbits in 57 patients with active GO (CAS ≥ 4) were entered into the study. All patients received corticosteroid treatment. Orbital DTPA uptakes were numerically quantified for the entire orbit as well as the anterior and posterior segments separately. DTPA SPECT was performed before, and 2 to 9 months after the initiation of immunosuppressive treatment. The normal range for DTPA uptake was established in 34 orbits of 17 patients who were being worked up for Raynaud's phenomenon and had no thyroid disease. Results: The mean DTPA uptake of the 114 orbits of GO patients was higher prior to corticosteroid therapy than after this treatment (11.03 ± 4.26 MBq/cm 3 and 9.84 ± 3.51 MBq/cm 3 , respectively, p 12.28 MBq/cm 3 for a substantial decline in DTPA uptake (favorable treatment outcome) was 76%, while a negative predictive value of a pretreatment DTPA ≤12.28 MBq/cm 3 was 78%. Conclusions: Corticosteriod treatment is associated with a decline in DTPA uptake in a fraction of GO patients. GO patients with a DTPA uptake above 12.28 MBq/cm 3 are more likely to have a favorable response to corticosteroid therapy while patients with lower values are less likely to have this potentially favorable response. An elevated DTPA uptake may identify patients who are most likely to benefit from immunosuppressive treatment.