Hyperthyroidism due to a pituitary TSH secreting tumour with amenorrhoea-galactorrhoea

A 20-year-old female presented with thyrotoxicosis associated with amenorrhoea and galactorrhoea after oral contraceptive withdrawal. Serum TSH was persistently elevated (mean: 28 +/- 3.1 microU/ml during 24-h sampling and did not vary significantly after TRH, bromocriptine or somatostatin. Prolactin levels remained constantly at the upper limit of normal (mean: 20.6 +/- 2.1 ng/ml, with a minimal increase after TRH, a slight decrease after somatostatin (54%) and a marked decrease after bromocriptine (88.5%). Surgical exploration revealed an unusually firm tumour adherant to the wall of the sella turcia; electron microscopic study showed that it was composed almost exclusively of thyrotrophs. After a transient period of euthyroidism post-operatively, T3 toxicosis occurred with an increased TSH level (15.5 microU/ml) and a rise in TSH and alpha subunit in response to TRH. An increase in T4 followed while prolactin remained low.