[Thelarche praecox - gray zone of precocious puberty].

Premature breast enlargement (premature thelarche) is not uncommon in girls younger than 8 years with the highest incidence below 2 years of age. It is usually a benign non-progressive condition. The pathogenesis of premature thelarche is unknown and controversial. Some authors suggest that it results from the abnormal sensitivity of the breast tissue to the small physiological amounts of estrogens. According to the results of some clinical investigations it may be due to the partial activation of hypothalamic-pituitary gonadal axis which affects FSH only. Such findings have not been confirmed by other clinical studies. Elevated FSH levels in younger girls seem to stem rather from delayed inactivation of the hypothalamic-pituitary gonadal axis, and in girls older than 3 years FSH levels were found to be not statistically different than in normal girls matched for age. Pelvic US in girls with premature thelarche usually reveals uterus and ovaries of prepubertal size. However, in girls with early stage of true precocious puberty similar pattern can be found. Exaggerated thelarche or thelarche variant, in which bone age acceleration or elevated estradiol levels may be present, can be a clinical challenge. In the differential diagnosis LHRH-analogue stimulation test with estradiol estimation seems to be particularly useful. Regular follow-up of the patients with PT, carried out until normal puberty develops is essential to rule out a progression of symptoms.