A case of idiopathic hypothalamic hypothyroidism

The availability of thyrotropin hormone (TRH) has made it possible to determine whether tropic hormone deficiency is caused by pituitary or hypothalamic dysfunction. A case of hypothalamic hypothyroidism was described ina a 17 year old woman. This patient was admitted for the evaluation of hypothyroidism and secondary amenorrhea. Her T3 and T4 were decreased, with an undetectable level of base line thyrotropin. the TRH test revealed normal but delayed response of TSH. Her base line prolactin and its response to TRH were normal. Adenocorticotropic hormone (ACTH), cortisol, growth hormone (GH), and urinary 17-hydroxysteroids were also normal. ACTH response to metyrapone was normal. Evaluation of the pituitary-gonadal axis revealed a normal increase in both lutenizing hormone (LH) and follicle stimulating hormone (FSH) following the intravenous administration of lutenizing hormone releasing hormone (LHRH). These results suggest that she had hypothalamic hypothyroidism as an isolated disturbance in the hypothalamic-pituitary axis. A deficiency of TRH is probably caused by a disorder of hypothalamic function of unknown etiology since the extensive studies did not reveal any secondary causes. It is recommended that patients with amenorrhea and hypothyroidism be evaluated for possible hypothalamic hypothyroidism.