Hypothalamic-pituitary causes

Hypogonadotrophic hypogonadism is characterised by a selective failure of the pituitary gland to produce luteinising hormone and follicle stimulating hormone. The commonest cause is excessive exercise, being underweight, or both. Women who have a low body mass index (weight (kg)/(height (m)²)) (for example, < 20) or who exercise excessively—for example, gymnasts, marathon runners, ballerinas—may develop amenorrhoea because of a physiological reduction in the hypothalamic production of gonadotrophin releasing hormone. Women who are underweight for their height when they get pregnant are more likely to have “small for dates” babies; and children of women who have eating disorders are more likely to be admitted to hospital with failure to thrive.

Sheehan's syndrome (panhypopituitarism), caused by infarction of the anterior pituitary venous complex (usually after massive postpartum haemorrhage or trauma), and Kallman's syndrome (amenorrhoea with anosmia caused by congenital lack of hypothalamic production of gonadotrophin releasing hormone) are rare. Children treated for a craniopharyngioma or some forms of leukaemia may have hypogonadotrophic hypogonadism secondary to cerebral irradiation, which may affect the hypothalamus or the pituitary.

Hyperprolactinaemia is usually caused by a pituitary microadenoma. …