Comparison of iodine-123 epidepride and iodine-123 IBZM for dopamine D2 receptor imaging in clinically non-functioning pituitary macroadenomas and macroprolactinomas

We compared pituitary iodine-123 epidepride single-photon emission tomography (SPET) and I-123-IBZM SPET for the in vivo imaging of dopamine D-2 receptors in 15 patients with clinically non-functioning pituitary adenomas. Four patients with dopamine agonist-sensitive macroprolactinomas were studied as positive controls. The uptake of radioactivity in the pituitary was established using a visual scoring system and an uptake index calculated by dividing the average count rates in the pituitary area by the average count rates in the cerebellum. All four macroprolactinomas showed specific binding of I-123-epidepride, but only one showed specific binding of I-123-IBZM. Specific binding of I-123-epidepride was demonstrated in 9 of the 15 clinically nonfunctioning pituitary adenomas (60%), but specific binding of I-123-IBZM was shown in only 6 of these 15 cases (40%). The uptake of I-123-epidepride in the pituitary region was consistently higher than that of I-123-IBZM. 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 visualization of dopamine receptor-positive pituitary adenomas. Therefore, I-123-epidepride should replace I-123-IBZM for future D-2 receptor SPET studies of pituitary adenomas. I-123-epidepride SPET potentially might serve to predict the response of clinically non-functioning pituitary adenomas to dopamine agonist therapy.