Gonadotropin-releasing hormone testing in premature thelarche.
Premature thelarche (PT) is characterized by isolated breast development in girls prior to 8 years of age. In addition, there is neither growth spurt nor advanced bone age. It has been suggested that luteinizing hormone (LH) response to gonadotropin-releasing hormone (GnRH) alone is adequate to distinguish central precocious puberty from PT. However, LH response to GnRH is greater in infancy than that in childhood. Therefore, gonadotropin response to GnRH in girls with isolated premature breast development in different age group was studied. Thirty-six girls with isolated PT (aged 0.25-8 years) were evaluated. They were classified into 2 groups; aged < 4 years (group A: mean age 1.57 +/- 0.87 years, n = 13) and > or = 4 years (group B: mean age 6.97 +/- 0.94 years, n = 23). Initial evaluation included X-ray bone age, pelvic sonography and GnRH testing. Patients were followed for at least 1 year to confirm that no patient had progression into puberty. Bone ages in both groups were within mean +/- 2 SD in all patients. Pelvic sonography was performed in all patients which revealed no abnormality of ovaries and uterus. Pubertal response to GnRH stimulation is characterized by peak LH of > 20 IU/L or delta LH of > 15 IU/L which is generally greater than peak follicle stimulating hormone (FSH) or delta FSH, respectively. Mean peak LH and delta LH in group A were 13.0 +/- 6.06 and 11.4 +/- 5.92 IU/L whereas those in the group B were 8.5 +/- 4.10 and 6.3 +/- 3.49 IU/L. Therefore, LH response to GnRH in group A was significantly higher than that in group B (p < 0.05). In addition, the mean peak FSH and delta FSH in group A were 120.5 +/- 45.87 and 109.9 +/- 42.09 IU/L whereas those in the group B were 48.7 +/- 24.05 and 39.9 +/- 23.69 IU/L. Therefore, FSH response to GnRH in group A was significantly greater than that in group B (p < 0.001). LH response to GnRH alone can distinguish prepuberty from puberty in girls > 4 years of age. However, in prepubertal young girls with PT aged < 4 years, pubertal LH response can occur, i.e. peak LH > 20 IU/L. Hence, the greater FSH response to GnRH than that of LH would confirm the diagnosis of premature thelarche in this group. Therefore, the evaluation of FSH response to GnRH is beneficial to distinguish puberty from prepuberty in young girls.