Precocious puberty

What it is

Precocious puberty is puberty that starts too early: under 9 years in boys, and in girls under 8 years, given elsewhere as under 7 to 8 years. It divides into a central, gonadotropin dependent form, a peripheral, gonadotropin independent form, and benign precocious variants. They are also divided a second way: isosexual development, which follows the sex of the child, heterosexual development, which is feminization in a boy or virilization in a girl, and isolated pubarche, meaning pubic and axillary hair alone.

Causes and risk

In the central form GnRH is high and LH is high. Causes: idiopathic, most common in girls; CNS lesions, among them congenital defects and septo-optic dysplasia; intracranial tumors, above all hypothalamic hamartoma, the most common brain lesion causing it, and optic glioma, arachnoid cysts and astrocytoma; CNS injury from head trauma, cranial irradiation, cerebral palsy and infections such as tuberculous meningitis; hydrocephalus; myelomeningocele; radiation; tuberous sclerosis and neurofibromatosis type 1; familial precocious puberty; and prolonged exposure to elevated sex steroids, which covers McCune-Albright syndrome and late treatment of congenital adrenal hyperplasia.

The two sexes are not at the same risk, and the reason is at the gonad. The ovaries are very sensitive to the secretion of gonadotrophins from the pituitary gland, so gonadotrophin-dependent precocious puberty is fairly common in girls, where it is usually idiopathic or familial and a pathological cause is rare. The testes are relatively insensitive to the same secretion, so gonadotrophin-dependent precocious puberty is uncommon in boys, and there it is important to exclude a pathological cause.

In the peripheral form sex hormones come from peripheral synthesis or exogenous exposure; LH is low. In boys: congenital adrenal hyperplasia, virilizing tumors such as a Leydig cell tumor and gonadoblastoma, adrenal tumors, testotoxicosis, and familial male-limited precocious puberty. In girls: McCune-Albright syndrome, whose classic triad is precocious puberty, café-au-lait macules and polyostotic fibrous dysplasia; ovarian tumors such as a juvenile granulosa cell tumor; ovarian cysts, including an autonomous functional ovarian cyst; feminizing adrenal tumors; exogenous estrogen ingestion. Tumors that make hCG act predominantly in boys: dysgerminoma, germinal cell tumors, sex cord stromal tumors, and also hepatoblastoma, hepatoma and mediastinal tumor. Exogenous androgens such as anabolic steroids belong on the same list. Primary hypothyroidism and obesity are listed. In McCune-Albright syndrome the classic presenting sign of the precocious puberty is vaginal bleeding, the other common endocrine association is hyperthyroidism, and the inheritance is sporadic, from a mutation in the GNAS1 gene, and it is more common in girls.

Hypothyroidism is named apart, since it is usually associated with delayed pubertal development, and only on rare occasions, in prolonged and untreated disease, may precocious puberty ensue; that is the Van Wyk Grumbach syndrome, and it was proposed that it results from the overproduction of gonadotropins due to the loss of negative feedback on the pituitary.