Endocrine Abstracts

Background: Giant prolactinomas are uncommon pituitary tumours that can cause marked hormone excess and mass effect. Dopamine agonists are usually very effective, but some patients develop resistance or side effects when treated at high doses for long periods.

Case: A 21-year-old man presented with progressive visual loss and headaches. MRI showed an 8-cm sellar mass invading both cavernous sinuses and the tentorium. His serum prolactin was 794,560 mIU/l. He was started on cabergoline 14 mg per week—well above standard dosing—and was lost to follow-up for almost a decade. When reviewed again, his prolactin remained elevated (15,000 mIU/l) and MRI demonstrated persistent invasive disease. He also described compulsive gambling and excessive spending, consistent with a dopamine-agonist-related impulse control disorder. Echocardiography excluded valvular disease. The pituitary multidisciplinary team advised tapering cabergoline and reconsidering radiotherapy, given limited surgical options and incomplete biochemical response.

Discussion: This case highlights the problems that can arise when long-term cabergoline therapy is not closely monitored. Resistance to dopamine agonists and the emergence of behavioural side effects can complicate management and require a reassessment of treatment goals.

Conclusion: Giant prolactinomas resistant to dopamine agonists remain difficult to manage. Ongoing endocrine, neurosurgical and psychiatric follow-up is essential to balance tumour control with treatment safety.