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D2-receptor imaging has limited use in patients with nonfunctioning pituitary adenoma

de Herder WW et al. (2006) Dopamine agonist therapy of clinically non-functioning pituitary macroadenomas. Is there a role for 123I-epidepride dopamine D2 receptor imaging? Eur J Endocrinol 155: 717–723

Surgery is the preferred treatment for clinically nonfunctioning pituitary macroadenoma, but these tumors often recur. Since some of these tumors express dopamine D2 receptors, dopamine-agonist therapy has been explored as an alternative to surgery and as a postoperative treatment, with favorable albeit heterogeneous results; de Herder and colleagues, therefore, investigated whether single-photon-emission CT (SPECT) imaging with 123I-epidepride, a radiolabeled dopamine D2 receptor antagonist, could predict patients' responses to dopamine-agonist therapy.

Of 54 patients with clinically nonfunctioning pituitary adenoma who underwent SPECT, 18 patients (age range 32–86 years; 12 men) received dopamine-agonist therapy with quinagolide (150–300 µg daily) or cabergoline (1–2 mg weekly, titrated as required), for 34–187 months (mean 7.5 years). Five patients had previously undergone surgery and one required surgery after dopamine-agonist therapy was initiated. The other 36 patients required surgery or refused dopamine-agonist therapy. Patients underwent pituitary MRI at baseline, after 3–6 and 12 months of treatment, and annually thereafter.

Mean tumor shrinkage was 30% in cabergolide-treated and quinagolide-treated patients, which suggested that both agents reduced the need for postoperative radiotherapy. Pituitary uptake of 123I-epidepride did not predict patients' responses to dopamine-agonist therapy, although when tumor shrinkage was defined as a decrease of >20% on MRI, there was a trend for shrinkage to correlate with uptake of 123I-epidepride, especially for tumors with moderate uptake.

The authors conclude that 123I-epidepride SPECT is most useful to differentiate scar tissue from recurrent or residual tumor.

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D2-receptor imaging has limited use in patients with nonfunctioning pituitary adenoma. Nat Rev Endocrinol 3, 202 (2007). https://doi.org/10.1038/ncpendmet0408

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