Correlation of scintigraphic results using I-123-methoxybenzamide with hormone levels and tumor size response to quinagolide in patients with pituitary adenomas

The efficacy of dopaminergic agents in the medical treatment of pituitary adenomas is well known. Quinagolide is a nonergot derivative dopamine agonist, which binds dopamine D-2 receptors with high affinity. The treatment with this drug is reported to suppress hormone levels and to cause tumor shrinkage in prolactinomas and in a few GK-secreting pituitary adenomas. In clinically nonfunctioning pituitary adenomas (NFPA), the efficacy of quinagolide treatment is controversial. The scintigraphy of the pituitary region using I-123-methoxybenzamide (I-123-IBZM) allows US to visualize in vivo the expression of dopamine D-2 receptors on pituitary tumors. In this study, the pituitary scintigraphy with I-123-IBZM was performed in 14 patients with macroadenoma before starting a long-term treatment with quinagolide: 6 NFPA with high circulating alpha-subunit levels, 4 PRL-secreting, and 4 GH-secreting adenomas. A 3-point score was used to grade the ligand accumulation within the pituitary adenomas: 0 = negative, 1 = moderate uptake (equal to that recorded in the cerebral cortex), and 2 = intense uptake (equal to that recorded in the basal nuclei). The treatment with quinagolide was carried out at the dose of 0.3-0.6 mg/day for 6-12 months. Clinical, biochemical and hormonal assessment was repeated monthly during the first 3 months, then quarterly. Sellar magnetic resonance imaging was performed before and after 6 and 12 months of quinagolide treatment, to evaluate tumor shrinkage (>25% of baseline size).