Endocrine Abstracts

Prolactinomas are the most common functional pituitary tumours. Therapy is with dopamine agonists (DA). Cabergoline is frequently used as a first line agent; resistance to therapy is seen to other DA. We present a case of a 32 year old woman who moved to our area in the 1st trimester of pregnancy. She was known to have macroprolactinoma (maximal diameter > 1 cm), impinging on the optic chiasm. She was on cabergoline 0.5 mg once daily, but this was discontinued with no complications during pregnancy. Cabergoline 0.5 mg weekly was restarted 9 months postpartum, but serum prolactin remained elevated (5768 mIU/l; Normal Range: 102–496) and titration to 1 mg twice a week reduced this to 4054 mIU/l. Compliance was good. Therapy was changed to quinagolide rather than further increase in cabergoline dose, and a daily dose of 150 mcg reduced serum prolactin to 106 mIU/l. There was no change in the size of the adenoma on MRI, but there was no longer any impingement on the optic chiasm. Both quinagolide and cabergoline are selective D2 receptor agonists. Cabergoline resistance (which can be described as lack of response to a weekly dose ≥ 2 mg) is uncommon and tends to occur in macroprolactinomas. Increasing the dose further may prove effective, but carries an increased risk of side effects. Patients resistant to bromocriptine or quinagolide have been successfully treated by using cabergoline instead. This is the first case to our knowledge of a macroprolactinoma resistant to cabergoline, but responding to quinagolide.