**2.6 Hyperprolactinaemia**

Radiation-induced hyperprolactinaemia is mostly seen following intensive irradiation due to hypothalamic damage leading to a reduction in the inhibitory neurotransmitter dopamine. It has been described in both sexes and all age groups but is most frequently encountered in the adult female with radiation doses in excess of 40 Gy. In these patients, a mild to modest elevation in prolactin level is noticed in 20-50% (Agha et al., 2005; Constine et al., 1993; Lam et al., 1991; Littley et al., 1989a; Samaan et al., 1987) compared with less than 5% in children (Rappaportet al., 1982) and after low radiation doses (Littley et al., 1991). A much higher incidence is seen following intensive irradiation; Chen et al (Chen et al., 1989) reported hyperpractinaemia in 21% and 36% in the first 4 years and after 15 years of radiotherapy in NCP, respectively.

Radiation-induced hyperprolactinaemia is not clinically significant in the vast majority of patients. Occasionally, it may be of sufficient severity to impair gonadotrophin secretion and cause pubertal delay or arrest in children, decreased libido and impotence in adult males and galactorrhoea and/or ovarian dysfunction in women (Samaan et al., 1982). A gradual decline in the elevated prolactin level may occur with time and can normalize in some patients. This may reflect time-dependent slowly evolving direct radiation-induced damage to the pituitary lactotroph (Littley et al., 1989b).

Radiation-induced hyperprolactinaemia responds very well to treatment with dopamine agonists. Galactorrhoea resolves soon after normalising prolactin levels. However, treatment with dopamine agonists will only restore gonadal function and fertility if there is no coexisting gonadotrophin deficiency or primary chemotherapy-induced gonadal damage.
