Primary hypothyroidism with hyperprolactinaemia and pituitary enlargement mimicking a pituitary macroadenoma.

Hyperprolactinaemia can occur in patients with hypothyroidism. A 32-year-old woman with primary hypothyroidism presented with amenorrhoea and galactorrhoea of two years' duration. She had hyperprolactinaemia, low basal morning cortisol levels and evidence of a pituitary macroadenoma on magnetic resonance imaging. Therapy with L-thyroxine resulted in induction of regular menses, resolution of galactorrhoea, normalisation of hormone levels and disappearance of the image of pituitary macroadenoma. It seems that enlargement of the pituitary due to thyrotroph and/or lactotroph cell hyperplasia secondary to hypothyroidism is responsible for this 'pseudotumour' image on radiological study. Recovery of her low basal cortisol values during treatment could also be explained by the dissolution of the pressure effect of enlarged pituitary in addition to the regression of hypothyroidism. In subjects with primary hypothyroidism and hyperprolactinaemia and pituitary enlargement, thyroid hormone replacement should be a first line treatment preceding pituitary surgery and bromocriptine use.