Inappropriate TSH secretion with abnormal thyrotroph sensitivity to dopamine.

A 47-year-old male schizophrenic with hyperthyroidism was found to have non-neoplastic inappropriate thyrotropin (TSH) secretion. Anterior pituitary function, CT scan and alpha subunit determinations were normal. TSH rose after TRH (7.8 to 22.5 microU/ml) and propylthiouracil (26.1 microU/ml after 3 months) and decreased with oral T3 (Cytomel 25 micrograms po q.i.d.). Cytomel and glucocorticoid infusion blunted but did not completely suppress the TSH response to TRH. Intravenous dopamine infusion (4 micrograms/kg/min) completely suppressed the prolactin but not the TSH response to TRH. The association of schizophrenia and differential thyrotroph sensitivity to dopamine suggests a possible role for dopamine in the pathogenesis of selected cases of non-neoplastic inappropriate TSH secretion.