MON-114 - A Paradoxical Endocrine Response to Cabergoline: Rising IGF-1 in Setting of Prolactinoma Treatment

Prolactinomas account for approximately 40% of pituitary adenomas. Oral dopamine agonists are the first-line treatment. Cabergoline, a dopamine D2 receptor agonist, is usually preferred over bromocriptine because of its greater efficacy in normalizing prolactin levels and achieving tumor shrinkage. Cabergoline is also used as an oral therapeutic agent in the treatment of mild acromegaly and is expected to lower IGF-1 levels; however, we have observed mild elevations in IGF-1 following dopamine agonist therapy. Here, we present three cases of patients with prolactinomas who developed elevated IGF-1 levels during dopamine agonist treatment.

There was a series of three patients (Patients A-C) in our institution with a history of either micro- or macroprolactinoma. All patients were treated either with cabergoline or bromocriptine. Both Patient A had B had baseline IGF-1 levels drawn prior to therapy which were found to be within normal range. Patient A experienced a 37% increase in IGF-1 after 13 months of therapy with Cabergoline 0.25 mg twice weekly while Patient B experienced a 79% increase in IGF-1 after 21 months of therapy with Cabergoline 0.25 mg weekly. Patient C also developed elevations of IGF-1 after 12 months of therapy, with Bromocriptine 2.5 mg daily. Patient B underwent an oral glucose tolerance test after holding cabergoline for 4 weeks, which was negative, successfully excluding acromegaly. Of note, these patients did not have any clinical signs or symptoms of growth hormone excess. This is clinically relevant as a correct diagnosis is crucial to prevent reduction or withdrawal of dopamine agonist therapy.

The mechanisms regarding IGF-1 increase during dopamine agonist therapy may be due to increased secretion of growth hormone from somatotroph cells, rather than a stimulatory effect of DA on IGF-1 production. Based on the data we reviewed, it is recommended to closely monitor these patients, as this could potentially increase the risk of developing acromegaly in the future. Patients should undergo baseline testing of IGF-1 prior to initiation of DA therapy. Although monitoring levels throughout therapy is not recommended, it is a vital clinical pearl to consider when treating patients.

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