Endocrine Abstracts

Background: Dopamine agonists (DA) are used as the first-line trearment in patients with macroprolactinomas. Late resistant to DA(cabergoline) therapy may occur. Patient with resistant macroprolactinoma may end up receiving a relative high dose of DA. These patients should be advised to take up radiotherapy option as earlier as possible to avoid the need of high dose dopamine agonist. We present a 63-year-old man who presented in 1999 with visual loss,due to giant macroprolactinoma compressing the optic chiasma(image1), his initial prolcatin level was >130 000 mIU/l. He responded well to cabergoline,with full recovery of his vision and prolactin maintained in the normal range (<500) on 1 mg/week of cabergoline. There was significant reduction in tumour size with small residual tumour extending into the right carvenous sinus. Prolactin levels gradually rose to >3000 over 2 years (2005–2007) despite moderate increase in cabergoline, but there was no change in tumour size. Few months later there was dramatic increase of prolactin to >20 000 associated with development of right 6th nerve palsy. MRI demonstrated significant tumour enlargement within the right carvenous sinus with replacement of sphenoid bone. The patient was offered radiotherapy at this stage but he declined. There was minimal response despite increasing cabergoline doses to 10 mg/week, and subsequently he underwent external beam radiotherapy in may 2008. Due to concerns of possible valvulopathy on long term high dose cabergoline (cummulative dose of 1.352 g up to June 2009), quinagolide was gradually introduced and cabergoline dose tapered down over 6 months. His ECHO revealed mild aortic regurgitation, with left ventricular dysfunction, and evidence of LBBB. Currently is 18 months post radiotherapy and remains on quinagolide 300md daily recent prolactin of around 3000 mIU/l. His 6th nerve palsy remains but with evidence of substantial tumour regression on MRI.

Discussion: Late-onset resistance to cabergoline can occur as demonstrated in our patient and in this case associated with aggressive tumour growth. Early radiotherapy should be considered, and switcing to different dopamine agonist which is not ‘ergot-derive’ may be beneficial both in terms of treatment response and avoiding risk of valvulopathy.