Endocrine Abstracts

The goals of treatment for a prolactinoma are to normalise serum prolactin and decrease the size of the tumour. Dopamine agonists (cabergoline is first-line) represent primary therapy for almost all prolactinomas. Some prolactinomas exhibit resistance to dopamine agonist treatment and require higher doses. Our patient was a 35-year-old male who presented to Ophthalmology in March 2021 with visual disturbance, confirmed to be secondary to a bitemporal hemianopia. OCT showed bilateral reduced RNFL thickness, worse on the right. Initial bloods revealed: prolactin 28 000 mIU/l(<300), FSH 2.9 IU/l,LH 1.7 IU/land testosterone 4.6 nmol/l. 9AM cortisol, thyroid function and IGF-1 were normal. MRI Pituitary showed a 3.5*2.5*2.6 cm suprasellar mass compressing the optic nerves and chiasm. He started cabergoline 250 mg twice a week with the dose gradually increased, aiming to reduce prolactin into the reference range and to restore normal gonadal function. Once the weekly cabergoline dose exceeded 2 mg/week, annual echocardiography was organised with close monitoring of behaviour for impulse control disorder throughout. Three months after starting cabergoline (June 2021), his visual fields showed some improvement. In August 2021, MRI pituitary revealed minimal change in the size of tumour in with compression of the chiasm and distortion of the pre-chiasmatic optic nerves, especially the right. The cabergoline dose was further increased to 4 mg/week. Serum prolactin steadily fell with normalisation of testosterone and corresponding improvement in libido and erectile function. Annual echocardiography was organised with close monitoring of behaviour for impulse control disorder throughout. However, further pituitary imaging again showed little reduction in the tumour size with ongoing chiasmal compression. At this stage his serum prolactin remained above the reference range at 744mU/l. To try to achieve further reduction in tumour size and normalise serum prolactin, cabergoline was increased to a weekly dose of 7 mg/week. This was tolerated well by the patient. Surprisingly, subsequent imaging revealed only a marginal reduction in tumour size despite a normal serum prolactin with ongoing mass effect on the optic chiasm. The patient underwent trans-sphenoidal pituitary surgery in March 2023. Post-operative MRI showed an excellent resection and we wait ophthalmology review post-operatively. Histology confirmed staining for GH and prolactin, with a Ki67 index of <3%. Since this histology may reflect a somatomammotroph adenoma, which is a more aggressive histopathological subtype, we will monitor this closely with imaging. We are interested why prolactin normalised with dopamine agonists (at high dose) but the tumour size did not change.