Endocrine Abstracts

Background: Current guidance for the management of macroprolactinomas recommends full pituitary profile at baseline and subsequently only if symptomatic. Pituitary adenomas that co-secrete growth hormone and prolactin at presentation are well-recognised. Case reports of acromegaly after prolactinoma treatment are associated with symptomatic acromegaly. We present two patients with asymptomatic acromegaly years after diagnosis of macroprolactinoma.

Patient 1: A 47-year old gentleman presented with erectile dysfunction and investigations confirmed hypogonadatrophic hypogonadism due to hyperprolactinaemia (prolactin 29,599mIU/l, testosterone 3nmol/l, LH 0.7IU/l). Remaining pituitary profile was normal, IGF-1 26.1nmol/l. MRI showed 28mm x 40mm macroprolactinoma, without optic nerve compression. He commenced cabergoline and subsequent MRI demonstrated significant reduction of the tumour. Pituitary profile 3.5 years later identified a raised IGF-1 (47.1nmol/l), failure to suppress GH during OGTT (nadir 1.5 mg/l) but no clinical features of acromegaly. He underwent pituitary adenomectomy. Histology confirmed a mixed somatotroph-lactotroph adenoma. Two months post-operatively, small residual adenoma remained with corresponding raised IGF-1 (34.5nmol/l) and prolactin (4403mIU/l).

Patient 2: A 39-year old woman investigated for subfertility, secondary amenorrhoea and galactorrhoea was found to have an elevated prolactin (2968mIU/l) and normal other pituitary hormones (IGF-1 20.2nmol/l). MRI demonstrated a microadenoma, cabergoline was commenced and prolactin normalised. Four years later, MRI showed a macroadenoma (16 x 10 x 10mm) stretching the optic chiasm with normal visual fields. The following year, she developed a severe headache due to pituitary apoplexy. Biochemistry found raised IGF (35nmol/l), prolactin (3009mIU/l), low TSH (0.38mU/l; T4 10.7pmol/l), cortisol (67nmol/l) and gonadotrophins. GH failed to suppress on OGTT (nadir 0.59 mg/l) and repeat MRI demonstrated reduction in tumour volume. She did not have clinical features of acromegaly.

Discussion: These cases demonstrate new-onset, asymptomatic GH co-secretion from macroprolactinomas. If there is interval growth or failure of tumour shrinkage with cabergoline, we suggest annual IGF-1 testing.