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 D2 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
GH-secreting pituitary adenomas. In clinically nonfunctioning
pituitary adenomas (NFPA), the efficacy of
quinagolide treatment is controversial. The scintigraphy of the pituitary region using 123I-methoxybenzamide (123I-IBZM) allows us to visualize in vivo the expression of
dopamine D2 receptors on
pituitary tumors. In this study, the pituitary scintigraphy with
123I-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). In all 14 patients, a significant positive correlation was found between the degree of
123I-IBZM uptake and the clinical response to
quinagolide treatment (r = 0.90; P < 0.001). In particular, the normalization of serum alpha-subunit and PRL levels, respectively, was achieved in 3 patients with NFPA and in 2 patients with
prolactinoma, who showed intense
123I-IBZM uptake in the pituitary region. In 4 of these 5 patients with positive scan, a significant
tumor shrinkage occurred between 6 and 12 months after the beginning of
quinagolide treatment. In all patients with GH-secreting
adenoma, no significant uptake of
123I-IBZM was found and no significant decrease of circulating GH and/or
insulin-like growth factor-I levels, and
tumor shrinkage was obtained during long-term treatment with
quinagolide. In conclusion, the pituitary scintigraphy with
123I-IBZM can be considered a useful tool to indicate
adenomas with significant expression of functioning D2 receptors. This innovative technique may predict the response to long-term treatment with
quinagolide in patients with NFPA, where the lack of pituitary
hormone hypersecretion makes difficult the monitoring of medical treatment efficacy.