Pubertas Prekoks

01Pathophysiology

Normal puberty begins when pulsatile GnRH secretion from the hypothalamus resumes after childhood quiescence, driving LH and FSH release, which in turn stimulates gonadal sex steroid production. Precocious puberty represents secondary sexual development before age 8 in girls and age 9 in boys, and it is mechanistically split into two pathways that the examiner expects you to differentiate confidently.

In central precocious puberty, the HPG axis is prematurely switched on. The pulse generator in the hypothalamus activates early, producing a normal but mistimed cascade: GnRH triggers LH and FSH, gonads enlarge and secrete estradiol or testosterone, and Tanner stages progress in the normal physiological sequence. This is why girls with central form develop breast tissue first (thelarche), then pubic hair (pubarche), then menarche, while boys show testicular enlargement greater than 4 mL as the earliest sign. The accelerated sex steroid exposure pushes the growth plate, producing the classic early growth spurt followed by premature epiphyseal fusion and short adult stature if untreated.

In peripheral precocious puberty, sex steroids appear without HPG activation. The source is the gonad itself (autonomous ovarian cyst, Leydig cell tumor), the adrenal gland (congenital adrenal hyperplasia, adrenal carcinoma), an ectopic hCG-producing tumor, or an exogenous hormone exposure. Because LH and FSH are suppressed by negative feedback, the testes remain prepubertal in size despite virilization, a finding that should immediately point you toward an adrenal or exogenous source in a boy. The exception is hCG-secreting tumors (hepatoblastoma, germ cell tumors), where hCG mimics LH and causes bilateral testicular growth.

A second key concept is secondary central precocious puberty: prolonged peripheral sex steroid exposure can mature the hypothalamus and trigger true central activation on top of the original peripheral process. This explains why untreated CAH or McCune-Albright syndrome can evolve into a mixed picture and why GnRH agonists may be added later.

02Classification and Clinical Manifestation

Two named syndromes appear repeatedly in vignettes.

• McCune-Albright syndrome is the triad of peripheral precocious puberty, polyostotic fibrous dysplasia, and café-au-lait macules with irregular borders that respect the midline. The underlying defect is a postzygotic activating mutation of the GNAS1 gene producing constitutive G-protein activation in affected tissues.

• Familial male-limited precocious puberty (testotoxicosis) results from an activating mutation of the LH receptor, causing autonomous Leydig cell testosterone production with suppressed LH; boys present at age 2 to 4 with virilization and modestly enlarged testes.

Types of Central Precoccious Puberty

Types of peripheral precoccious puberty

03Diagnostic Workup

The workup follows a logical sequence built around one question: is the HPG axis the driver, or is the sex steroid coming from somewhere else?

Begin with bone age as the first practical step. A bone age that matches chronological age in a child with apparent pubertal signs argues against true precocious puberty and favors a benign normal variant such as premature thelarche or premature adrenarche. An advanced bone age more than 2 SD above chronological age confirms that meaningful sex steroid exposure has occurred and justifies further evaluation.

Next obtain basal LH, FSH, and the dominant sex steroid (estradiol in girls, total testosterone in boys). Modern ultrasensitive assays detect a basal LH greater than 0.3 IU/L, which alone may confirm central activation. When basal levels are equivocal, proceed to the GnRH stimulation test, which is the gold standard. Synthetic GnRH (or a GnRH analog such as leuprolide) is administered, and LH is measured at intervals. A peak LH greater than 5 IU/L indicates a pubertal HPG axis and confirms central form; a blunted response with continued sex steroid elevation confirms peripheral form.

Once you have classified the process, target the source. For central form, obtain an MRI of the brain and pituitary to look for hypothalamic hamartoma, optic pathway glioma, or other lesion. MRI is mandatory in all boys with central form and in girls under age 6, since pathological causes are more common at younger ages. For peripheral form, the source determines the next test: pelvic ultrasound for ovarian pathology, adrenal CT or MRI for suspected adrenal tumor, 17-OHP for CAH, beta-hCG for hepatic or germ cell tumors, and a careful history for exogenous hormone exposure (creams, supplements, contaminated medications).

04Management and Treatment

The management framework hinges on the type. Central form is treated with GnRH agonists, which produce paradoxical suppression of the HPG axis after an initial flare. Continuous (rather than pulsatile) GnRH receptor stimulation downregulates pituitary GnRH receptors, shutting off LH and FSH and halting gonadal steroid production. Leuprolide depot is the workhorse: 7.5 mg intramuscularly every 4 weeks, or longer-acting formulations every 12 weeks. The histrelin implant placed subcutaneously delivers continuous drug for at least one year and is a practical option for adherence. Treatment is monitored by suppression of basal and stimulated LH, slowing of growth velocity, regression or stabilization of Tanner stage, and deceleration of bone age advancement. Therapy continues until a developmentally appropriate age, generally around 11 in girls and 12 in boys, after which puberty is allowed to resume.

Peripheral form demands treatment of the cause. In McCune-Albright syndrome, aromatase inhibitors (letrozole, anastrozole) block estrogen synthesis at the ovary, while tamoxifen blocks estrogen action at the receptor. Familial male-limited precocious puberty requires combined blockade: an antiandrogen (spironolactone, bicalutamide) plus an aromatase inhibitor to prevent androgen-driven bone maturation. Congenital adrenal hyperplasia is treated with hydrocortisone replacement to suppress ACTH and reduce androgen overproduction; fludrocortisone is added when there is salt-wasting. Tumors are resected. Once a peripheral process has been suppressed, watch for secondary central activation that may then require a GnRH agonist on top of the original therapy.

The "next best step" logic that recurs in vignettes is: confirm advanced bone age, classify the form with basal gonadotropins or a GnRH stimulation test, image the brain when central form is found, and start a GnRH agonist when central form is confirmed and progressive. Do not start a GnRH agonist before classification. Do not image the brain in a child with isolated premature thelarche and no advanced bone age.

05Differential Diagnosis and Distractors

06Traps and High-Yield Pearls

The most common error is failing to distinguish central from peripheral form before reaching for treatment. Vignettes will hand you a child with breast budding and advanced bone age and tempt you to choose a GnRH agonist. If basal LH is suppressed, GnRH agonists will not work; the source is elsewhere. Always anchor your reasoning on the gonadotropin pattern: pubertal LH points central, suppressed LH points peripheral.

The classic boys' trap centers on testicular size. Bilateral enlargement greater than 4 mL implies LH stimulation, which means either central form or an hCG-secreting tumor. Prepubertal testes with virilization implies adrenal androgens (CAH or adrenal tumor) because the gonad is not being stimulated. Asymmetric or unilateral enlargement with virilization implies a Leydig cell tumor. Sorting boys by testicular findings cuts the differential cleanly.

The hypothyroidism trap is favored by exam writers because it inverts the usual pattern: bone age is delayed, not advanced. A child with breast development, short stature, weight gain, and constipation, found to have profound primary hypothyroidism, has Van Wyk-Grumbach syndrome. Treating with levothyroxine resolves the precocious changes. Picking a GnRH agonist here is wrong.

McCune-Albright is a high-yield distractor that can be solved by reading the skin description carefully. Café-au-lait macules with irregular "coast of Maine" borders that respect the midline, combined with bone pain or fractures from polyostotic fibrous dysplasia, points away from idiopathic central form and toward peripheral form requiring an aromatase inhibitor or tamoxifen rather than a GnRH agonist.

For benign normal variants, the rescue cue is usually the bone age. Premature thelarche and premature adrenarche have bone ages within one year of chronological age, no progressive Tanner advancement, and normal growth velocity. Choosing extensive imaging or hormonal therapy in these children is an exam trap; the correct next step is reassurance and observation.

The core competency being tested is mechanistic classification followed by directed therapy: recognize the age-based threshold (under 8 in girls, under 9 in boys), confirm the process is real with bone age and basal gonadotropins, distinguish central from peripheral with a GnRH stimulation test, image the brain when central form is confirmed (always in boys), and treat the cause rather than the surface phenotype.