Speed of response to dopaminergic agents in prolactinomas

Purpose: Hyperprolactinemia in the presence of a sellar lesion can be caused by prolactin secretion from the lesion, or by increased intrasellar pressure/compression of the pituitary stalk (“stalk effect”). The objective of this work was to determine the response to dopamine agonists (DAs) in bona fide prolactinomas presenting with a prolactin range similar to what can be seen in nonhormonal secreting pituitary tumors. Methods: A descriptive study on 68 prolactinomas presenting with prolactin levels between 50 and 200 ng/mL in a tertiary center in the U.S.A. over 22 years. The main outcome was prolactin decrease from diagnosis to follow-up by 2 months from initiation of DA therapy. Results: With a median time to follow-up from starting DA therapy of 5 weeks [IQR:4, 6], the median prolactin check showed normality at 11.85 ng/mL [IQR: 5.1, 29]. The median prolactin percent change was at 87% [IQR:67, 94] by 2 months. The majority (75%) of patients presenting had a 2/3 (67%) prolactin drop by 2 months, with more than 1/4 (25%) having a percent drop >95%. Conclusions: A rapid decline in prolactin level can be seen in prolactinomas upon initiation of DA therapy. This significant prolactin drop restricts the ability to establish a threshold beyond which the diagnosis of prolactinoma could be excluded.