Precocious puberty in girls: pituitary height as an index of hypothalamo-pituitary activation.

The pituitary heights in 47 girls having breast development before 8 yr were measured by magnetic resonance imaging and compared to the normal values for age and to clinical and laboratory data. They were classified into 3 groups: 1) premature thelarche (PT), isolated breast development with plasma estradiol less than 74 pmol/L (8 cases); 2) mild form of central precocious puberty (CPP1) with an LH/FSH peak ratio after the LH-releasing hormone test less than 1 (22 cases); 3) classical form of CPP (CPP2) with an LH/FSH peak ratio greater than 1 (17 cases). All girls with CPP had breast and pubic hair development before 8 yr, accelerated growth velocity, and no intracranial lesion. The mean ages at breast development [7.2 +/- 0.4 (SE), 6.5 +/- 0.4, and 7.2 +/- 0.3 yr] and the mean times between breast development and magnetic resonance imaging evaluation (0.8 +/- 0.1, 0.8 +/- 0.2, and 0.9 +/- 0.1 yr) were similar in the 3 groups. The mean pituitary heights were 4.9 +/- 0.2 in PT, 5.1 +/- 0.2 in CPP1, and 6.2 +/- 0.2 mm in CPP2. They were not significantly different in PT and CPP1 but were significantly greater in CPP2 than in PT (P < 0.001) or CPP1 (P < 0.001). Individual values of pituitary height were compared to those of age-matched girls: they were greater than or equal to mean +/- 2 SD in 8% of PT, 32% of CPP1, and 70% of CPP2. In the CPP group, the pituitary height was correlated with the LH/FSH peak ratio [correlation coefficient (r = 0.52, P < 0.01] and plasma estradiol (r = 0.60, P < 0.01). Four patients with high pituitary height despite LH/FSH peak ratios less than 1 had an increase of their breast development within 1 yr. We conclude that the pituitary height is normal for age in girls with premature thelarche or a mild form of CPP. Conversely, pituitary height is in the pubertal range in girls with the classical form of CPP. Its correlation with LH/FSH peak ratio suggests that pituitary height reflects changes in the degree of hypothalamo-pituitary activation and may provide an indication of its future development. It may therefore help in decisions on LH-releasing hormone analog therapy in certain cases.