Thyrotropin-and prolactin--secreting pituitary tumor dissociated hormonal response to bromocriptine

A 41-year-old male with recurrent hyperthyroidism resulting from pituitary tumor was studied. Because of recurrent hyperthyroidism, he had been treated with propylthiouracil for four years and had been operated. At the time of high serum thyroid hormone (T4: 20 micrograms/dl; T3:502 ng/dl), there was also elevated basal serum TSH level (55 microU/ml) which could not be suppressed by exogenous thyroid hormone administration. In addition, the serum TSH showed blunt response to intravenous TRH infusion. An elevated serum prolactin level was also observed (111 ng/ml). After bromocriptine administration (2.5 mg daily), the suppressibility of serum TSH level was found better than that of prolactin level. The existence of a TSH- and PRL-secreting pituitary tumor in this patient exhibited a dissociated hormonal response to low doses of dopaminergic agents.