Hypothalamic hamartomas and precocious puberty

Gonadotrophin and prolactin secretory dynamics in girls with normal puberty, idiopathic precocious puberty and precocious puberty due to hypothalamic hamartoma

OBJECTIVE

This study was designed to test the hypothesis that hypothalamic hamartoma causes precocious puberty through a different neuroendocrine mechanism than that of normal puberty or of idiopathic precocious puberty.

DESIGN AND PATIENTS

We compared the pattern of gonadotrophin secretion among 4 girls with precocious puberty due to hypothalamic hamartoma, 27 girls with idiopathic precocious puberty, and 14 girls with normal puberty. All subjects were breast stage 3 or 4. Blood samples were obtained every 20 min for 4 h during the day (1.000 hours to 1400 h) and night (22.00 hours to 0200 h).

MEASUREMENTS

LH, FSH, and prolactin were measured in each blood sample. Girls also underwent LHRH-stimulation with measurement of LH and FSH before and after stimulation.

RESULTS

There were no significant differences in mean LH level, LH peak amplitude, or LH or FSH peak frequency during either the day or the night among the three diagnostic groups. However, the mean +/- SD LHRH-stimulated peak LH levels were greater in girls with hypothalamic hamartoma than in girls with normal puberty or with idiopathic precocious puberty (194 +/- 142 vs 85 +/- 60 or 66 +/- 54 IU/l, respectively, P < 0.05). The LHRH-stimulated peak FSH level in girls with hypothalamic hamartoma exceeded the level for the normal pubertal girls (31 +/- 19 vs 17 +/- 7 IU/l, P < 0.05), but not the level for the girls with idiopathic precocious puberty (25 + 12 IU/l). The peak LH to peak FSH ratio in the girls with hypothalamic hamartoma exceeded the ratio for the girls with idiopathic precocious puberty (7.3 +/- 3.9 vs 2.6 +/- 3.0 IU/l, P < 0.05), but not the ratio for the normal pubertal girls (5.0 + 2.9). There were no significant differences in mean prolactin level, peak amplitude or frequency, or in the ratio of mean night to mean day prolactin, among the 3 diagnostic groups.

CONCLUSIONS

We conclude that spontaneous gonadotrophin and prolactin secretion are similar among girls with hypothalamic hamartoma, idiopathic precocious puberty, or normal puberty. However, the increased LHRH-stimulated peak LH in the girls with hypothalamic hamartoma suggests subtle differences in neuroendocrine regulation that may underlie their more rapid pubertal maturation.

Precocious puberty

Puberty occurring before the age of 8 years in girls and 9 years in boys in considered precocious. The numerous causes of precocity can be classified as central or peripheral. Central or true precocious puberty (CPP) is due to premature activation of the hypothalamopituitary-gonadal axis and is isosexual. Peripheral or pseudoprecocious puberty (PPP) results from the production of sex steroids independent of the H-P-G axis and may be isosexual or heterosexual. CPP is the most common form of precocity involving more than 50% of children and is much more common in girls than boys. CPP is more common between 4 and 8 years. A peak serum LH levels > 10 iu/l following GnRH stimulation is the absolute evidence of CPP. Serum IGF-I levels are predictive of the outcome. Availability of CT and MRI has helped to determine the cause of CPP in most cases. Hypothalamic hamartoma is the most common tumour causing CPP especially in boys. Adrenal causes, particularly CAH, are the commonest cause of PPP in boys whereas ovarian causes are more likely in girls. Long acting GnRH analogues provide a safe and effective form of treatment of CPP.