Comparison of iodine-123 epidepride and iodine-123 IBZM for dopamine D-2 receptor imaging in clinically non-functioning pituitary macroadenomas and macroprolactinomas

We compared pituitary iodine-123 epidepride single-photon emission tomograp hy (SPET) and I-123-IBZM SPET for the in vivo imaging of dopamine D-2 recep tors in 15 patients with clinically non-functioning pituitary adenomas. Fou r patients with dopamine agonist-sensitive macroprolactinomas were studied as positive controls. The uptake of radioactivity in the pituitary was esta blished using a visual scoring system and an uptake index calculated by div iding the average count rates in the pituitary area by the average count ra tes in the cerebellum. All four macroprolactinomas showed specific binding of I-123-epidepride, but only one showed specific binding of I-123-IBZM. Sp ecific binding of I-123-epidepride was demonstrated in 9 of the 15 clinical ly nonfunctioning pituitary adenomas (60%), but specific binding of I-123-I BZM was shown in only 6 of these 15 cases (40%). The uptake of I-123-epidep ride in the pituitary region was consistently higher than that of I-123-IBZ M. None of the patients who showed absence of uptake of I-123-epidepride in the pituitary area showed uptake of I-123-IBZM in this area. In conclusion : I-123-epidepride SPET is superior to I-123-IBZM SPET for the visualizatio n of dopamine receptor-positive pituitary adenomas. Therefore, I-123-epidep ride should replace I-123-IBZM for future D-2 receptor SPET studies of pitu itary adenomas. I-123-epidepride SPET potentially might serve to predict th e response of clinically non-functioning pituitary adenomas to dopamine ago nist therapy.