Serum Levels of Thyroid Stimulating Hormone and Luteinizing Hormone Are Decreased in Girls with Central Precocious Puberty after 12-Month GnRH Agonist Treatment

Puberty is the transitional period from childhood to adult that leads to growth spurt, sexual maturation and attainment of reproductive capacity. Precocious puberty is defined when secondary sexual characteristics develop before the age of eight for girls and nine for boys. Central precocious puberty (CPP) is diagnosed when the process is driven by premature activation of hypothalamic gonadotropin-releasing hormone (GnRH) secretion. Many factors promote CPP, and the thyroid function is thought to be one of them. In our previous study, thyroid stimulating hormone (TSH) was higher in the CPP group than that of the participants without CPP. This elevation of TSH in CPP is said to be associated with pubertal luteinizing hormone (LH) elevation. The aim of this study was to evaluate the causal relationship between TSH and LH in CPP patients. A total of 221 girls diagnosed with CPP and treated with GnRH agonists were included. All participants except one showed LH suppression (peak LH < 3 IU/L), and serum levels of follicle stimulating hormone (FSH) were also lower after the treatment. These results indicate that puberty has slowed down and that the patients were successfully treated for CPP. As for thyroid hormones, TSH was significantly lower and free thyroxine (fT4) levels were higher after 12 months of GnRH agonist treatment compared with baseline. With GnRH agonist treatment, the serum levels of LH and TSH were decreased, suggesting that the increase in serum TSH levels is associated with premature LH elevation in girls with CPP.