[Hyperthyroidism and subjects hyperresponding to thyrotropin. Importance of simultaneous thyrotropin and prolactin determination following administration of thyroid-releasing hormone]

Abstract

Primary hypothyroidism is assessed by increased basal and TRH-induced TSH levels. Since basal and TRH induced prolactin (PRL) levels may also be modified by the thyroid status, TSH and PRL responses to TRH are simultaneously determined in patients with mild or evident primary hypothyroidism (n = 22) and in TSH hyperresponders (n = 28) with clinicobiological appearance of euthyroidism. In evident hypothyroidism (free thyroxine index FT4 I = 0,4 +/- 0,1) basal PRL are increased in 8 out of 11 patients and TRH-induced PRL responses are exaggerated in all cases like in mild hypothyroidism (FT 4 I = 1,2 +/- 0, 1) A negative correlation is found between maximal PRL levels and triiodothyronine (T3) levels (p less than 0,01). In presumed euthyroid TSH hyperresponders (FT4 I = 2,2 +/- 0,1) PRL response to TRH is exaggerated in only 7 patients and no correlation exists between maximal PRL and T3 levels. These data suggest that simultaneously exaggerated TSH and PRL responses to TRH are presumably patterns of potential hyperthyroidism for the diagnosis of which the determination of TSH alone seems to be necessary but insufficient.