Radiation-induced hyperprolactinaemia in a treated acromegalic.

A 31-year-old acromegalic was normoprolactinaemic after partial removal of her pituitary tumour. The post-operative external pituitary irradiation lowered the mean growth hormone (GH) level from 75 mU/1 to less than 1 mU/1 within 2 years. However, at the same time hyperprolactinaemia developed. These changes in the GH and prolactin levels were confirmed 3 and 4 years after irradiation. The cause of the hyperprolactinaemia was radiation-induced hypothalamic damage. Therefore it is suggested that similar damage may occur in patients receiving external pituitary irradiation for 'prolactinomas' and that this mechanism may contribute to the persistent hyperprolactinaemia observed in such patients.