Precocious Puberty

• Central (GnRH-dependent) precocious puberty follows the normal pubertal sequence and is driven by premature axis activation. It is far more often idiopathic in girls; in boys a central nervous system lesion (hamartoma, tumour, prior irradiation) must be excluded, so MRI of the brain is the higher-yield study in a boy.
• Peripheral (GnRH-independent) precocious puberty comes from autonomous sex steroid production — congenital adrenal hyperplasia, adrenal or gonadal tumours, McCune–Albright syndrome, exogenous hormone exposure — and the sequence is often out of order.
• The distinguishing test is a GnRH stimulation test: a pubertal LH rise indicates central disease, a suppressed LH indicates peripheral.
• Both accelerate skeletal maturation, so bone age exceeds chronological age and untreated disease shortens final adult height through early epiphyseal fusion.

Central (GnRH-dependent) — premature activation of the axis

• Idiopathic: the large majority of girls. A diagnosis of exclusion after imaging.
• CNS structural lesions: hypothalamic hamartoma (the classic lesion, may present with gelastic seizures), optic pathway glioma (think neurofibromatosis type 1), astrocytoma, craniopharyngioma, hydrocephalus, arachnoid cyst. Far more likely in boys and in any child under 6.
• Acquired CNS insult: cranial irradiation for leukaemia or brain tumour, head trauma, meningitis/encephalitis, perinatal injury.
• Genetic: loss-of-function MKRN3 mutations (paternally inherited because the gene is maternally imprinted) and gain-of-function kisspeptin-pathway mutations.
• Secondary central activation: prolonged peripheral sex-steroid exposure (e.g. late-treated congenital adrenal hyperplasia) primes the hypothalamus, so the axis switches on once the peripheral source is corrected.

Peripheral (GnRH-independent) — autonomous steroid production

• Adrenal: 21-hydroxylase deficiency congenital adrenal hyperplasia; adrenal adenoma or carcinoma.
• Gonadal: Leydig cell tumour (asymmetric testicular enlargement), granulosa cell tumour, autonomous ovarian cyst.
• McCune–Albright syndrome: mosaic activating GNAS mutation.
• **Familial male-limited precocious puberty (testotoxicosis)**: activating LH-receptor mutation.
• hCG-secreting tumours: hepatoblastoma, mediastinal or intracranial germ cell tumours — virilise boys only, since hCG alone drives Leydig cells but ovarian oestrogen synthesis also requires FSH.
• Severe primary hypothyroidism (Van Wyk–Grumbach) and exogenous exposure to topical testosterone or oestrogen creams.

Risk factors examiners plant

• Non-modifiable: female sex, Black or Hispanic ancestry, family history, prior CNS irradiation or injury, international adoption.
• Modifiable: obesity/high BMI (leptin-related, mainly in girls), and household exposure to a parent's transdermal sex-steroid gel or oestrogenic endocrine disruptors.

The normal brake

• Through childhood the GnRH pulse generator in the arcuate nucleus is actively restrained. MKRN3 and related factors suppress kisspeptin neurons; puberty begins when this inhibition is released and pulsatile GnRH resumes, driving LH more than FSH, then gonadal steroidogenesis.

Central mechanism

• Any lesion that disinhibits or ectopically drives the pulse generator — a hamartoma containing its own GnRH-secreting neurons, mass effect, or radiation injury to inhibitory pathways — restores pulsatile GnRH prematurely. Because the entire axis is engaged, puberty is isosexual and follows the normal sequence (thelarche → pubarche → growth spurt → menarche in girls; testicular enlargement first in boys). Bilateral testicular enlargement is the physical signature that gonadotrophins, not extragonadal steroids, are doing the work.

Peripheral mechanism

• Sex steroids arrive independent of GnRH, so hypothalamic GnRH and pituitary LH are suppressed by negative feedback. Testes therefore stay prepubertal in size despite virilisation (except in testotoxicosis or a unilateral Leydig cell tumour, where the gonad itself is the source). Adrenal androgen excess produces pubarche, acne and phallic growth without testicular growth — the out-of-sequence pattern.
• In McCune–Albright syndrome a post-zygotic activating GNAS mutation locks Gsα in the GTP-bound state, so cAMP is generated without ligand in affected tissues: autonomous ovarian cysts (oestrogen, vaginal bleeding), fibrous dysplasia in bone, hyperfunctioning thyroid, and hyperpigmented patches. Mosaicism explains why lesions are unilateral and irregular.
• In severe hypothyroidism, grossly elevated TSH cross-activates the FSH receptor — a rare cause in which bone age is delayed rather than advanced.

Common downstream endpoint

• Oestrogen (from ovarian output, or from aromatisation of androgens in boys) accelerates chondrocyte maturation, so linear growth accelerates but epiphyseal fusion is brought forward. The child is tall for age yet loses growth potential — the paradox of early tall stature with short final adult height.

The stem's typical child

• A girl aged 5–8 brought for breast development, often with a high BMI, or a boy under 9 with pubic hair and enlarging genitalia — a presentation that is far more likely to be pathological.

Central pattern (ordered, isosexual)

• Girls: breast budding first (oestrogen effect on ductal tissue), then pubic/axillary hair, growth spurt, and menarche typically about 2–3 years after thelarche.
• Boys: bilateral testicular enlargement above prepubertal volume is the earliest finding — gonadotrophin-driven seminiferous tubule growth — followed by phallic growth, pubic hair, voice deepening and acne.
• Growth acceleration with height crossing percentile lines upward, and advanced bone maturation on exam of the hands.

Peripheral pattern (disordered)

• Virilisation without testicular enlargement points to an adrenal source (congenital adrenal hyperplasia, adrenal tumour).
• Unilateral testicular enlargement suggests a Leydig cell tumour; symmetric enlargement out of proportion to a suppressed axis suggests testotoxicosis.
• Vaginal bleeding preceding or without breast development suggests an autonomous ovarian cyst or exogenous oestrogen.

Syndrome-specific clues

• McCune–Albright: large café-au-lait macules with irregular "coast of Maine" borders that respect the midline, polyostotic fibrous dysplasia with limp, bone pain or pathological fracture, plus recurrent oestrogen-secreting ovarian cysts causing intermittent vaginal bleeding.
• Hypothalamic hamartoma: gelastic (laughing) seizures, headache, visual field loss.
• NF1: multiple café-au-lait spots with smooth "coast of California" borders, axillary freckling, Lisch nodules.
• Congenital adrenal hyperplasia: clitoromegaly, severe acne, muscular build, salt-wasting history.

Benign mimics to recognise on exam

• Premature thelarche: isolated breast tissue in a toddler, normal growth velocity, normal bone age.
• Premature adrenarche: isolated pubic/axillary hair and body odour with normal growth and near-normal bone age.

Step 1 — establish that puberty is truly advanced

• Detailed Tanner staging, growth velocity plotted on a curve, review of prior heights, and a search for exogenous hormone exposure and CNS symptoms.
• Bone age radiograph of the left hand and wrist, read against the Greulich and Pyle atlas. A bone age exceeding chronological age (classically by more than about 2 standard deviations) confirms sex-steroid–driven skeletal advancement; the Bayley–Pinneau method converts this to a predicted adult height. A normal bone age points instead to benign premature thelarche or adrenarche.

Step 2 — is it central or peripheral?

• Basal LH by an ultrasensitive (third-generation) assay, ideally early morning: a pubertal-range LH essentially establishes central precocious puberty. A low LH does not exclude it.
• GnRH (or GnRH agonist, e.g. leuprolide) stimulation test is the reference standard: an LH-predominant pubertal rise confirms central disease; flat, suppressed LH with elevated oestradiol or testosterone confirms peripheral disease.

Step 3 — find the cause

• Central: MRI of the brain with pituitary/hypothalamic views — mandatory in all boys and in girls under 6, and in any child with neurological signs or rapid progression, per Pediatric Endocrine Society/ESPE consensus practice. Look for hamartoma, glioma, craniopharyngioma.
• Peripheral: pelvic ultrasound (ovarian cyst or tumour, uterine volume), testicular ultrasound if asymmetric, adrenal imaging; 17-hydroxyprogesterone (congenital adrenal hyperplasia), DHEAS, β-hCG and AFP (germ cell tumour, hepatoblastoma), TSH and free T4 (severe hypothyroidism with delayed bone age), and skeletal survey plus GNAS testing when McCune–Albright is suspected.

Interpretive traps

• A suppressed LH with high testosterone and prepubertal testes means the source is extragonadal — look at the adrenals.
• Peripheral disease can secondarily trigger central puberty; a repeat stimulation test after treating the peripheral source is sometimes needed.

Decide first whether treatment is needed

• Slowly progressive or non-progressive variants (isolated premature thelarche, premature adrenarche, a girl close to age 8 with normal bone age and preserved height prediction) are managed with serial observation of growth velocity, Tanner stage and bone age every few months. Treating these offers no height benefit.

Central precocious puberty — first line

• GnRH agonists (leuprolide acetate depot intramuscularly, monthly or every 3 months; histrelin subcutaneous implant replaced annually; triptorelin depot). Continuous, non-pulsatile receptor occupancy downregulates and desensitises pituitary GnRH receptors, shutting off LH/FSH — the therapeutic use of the same physiology that makes pulsatility essential. Expect a transient flare in the first weeks, occasionally with withdrawal vaginal bleeding.
• Goals per the Pediatric Endocrine Society/ESPE (Lawson Wilkins) consensus on GnRH analogue use: halt or regress secondary sexual characteristics, slow bone-age advancement and preserve adult height. Monitor clinically plus suppressed stimulated LH; treatment is usually stopped around the normal age of puberty, after which the axis reactivates and fertility is preserved.
• Adjunct: growth hormone is considered only in selected children with markedly compromised height prediction.

Peripheral precocious puberty — treat the source

• Congenital adrenal hyperplasia: glucocorticoid replacement (hydrocortisone) ± mineralocorticoid to suppress ACTH-driven androgens.
• Tumours (Leydig cell, granulosa cell, adrenal, hCG-secreting): surgical resection is definitive; oncological therapy as indicated.
• McCune–Albright syndrome in girls: aromatase inhibitor (letrozole) or selective oestrogen receptor modulator (tamoxifen) to blunt oestrogen effect.
• Testotoxicosis: androgen receptor blocker (bicalutamide or spironolactone) plus an aromatase inhibitor.
• Severe hypothyroidism: levothyroxine reverses the process.
• Remove any exogenous hormone source and counsel on transdermal gel transfer.

Contraindicated or futile

• GnRH agonists do not work in peripheral disease — the pituitary is already suppressed. They are added only if secondary central activation develops after the peripheral source is controlled.

Of the disease

• Short final adult stature: oestrogen-driven premature epiphyseal fusion. The signal is a child who is tall for age with a bone age far ahead of chronological age and a falling predicted adult height — the main reason to treat.
• Psychosocial morbidity: body-image distress, behavioural problems, teasing, and early menarche in a cognitively young child; heightened vulnerability to sexual abuse, which should be screened for.
• Missed underlying malignancy or CNS lesion — an emergency. Headache, vomiting, visual field defect or papilloedema suggests a hypothalamic/pituitary tumour with raised intracranial pressure; a virilising abdominal mass may be adrenal carcinoma or hepatoblastoma.
• Adrenal crisis in undiagnosed salt-wasting congenital adrenal hyperplasia — hypotension, hyponatraemia, hyperkalaemia; an emergency requiring stress-dose hydrocortisone, saline and glucose.
• McCune–Albright: pathological fracture and deformity from fibrous dysplasia, plus hyperthyroidism, growth hormone excess and hypophosphataemic rickets from FGF23 excess.
• Long term: early menarche is associated with adverse metabolic and cardiovascular risk profiles and with higher lifetime breast cancer risk, though causality is not established.

Of treatment

• GnRH agonist flare: transient rise in gonadotrophins with breast enlargement or vaginal bleeding in the first weeks.
• Injection-site reactions and sterile abscess with depot leuprolide; implant site infection or breakage with histrelin.
• Reduced bone mineral density accrual during suppression, largely recovering after discontinuation; ensure calcium and vitamin D adequacy.
• Slipped capital femoral epiphysis, reported with rapid changes in sex-steroid milieu — a limping child with hip or referred knee pain needs urgent imaging.
• Glucocorticoid over-treatment in congenital adrenal hyperplasia: growth suppression, Cushingoid features, weight gain.
• Aromatase inhibitors/antiandrogens: incomplete control of bone-age advance, and gynaecomastia with antiandrogens in boys.

• Testicular size is the free answer in boys: bilateral enlargement = central (gonadotrophin-driven); prepubertal testes with virilisation = adrenal source (congenital adrenal hyperplasia or adrenal tumour); unilateral enlargement = Leydig cell tumour.
• Single best next step in almost every stem is a bone age film of the left hand and wrist; a normal bone age with normal growth velocity redirects you to benign premature thelarche or premature adrenarche, not true precocious puberty.
• Central precocious puberty in a boy demands brain MRI — pathology is the rule, not the exception. Hypothalamic hamartoma with gelastic (laughing) seizures is the eponymous association examiners love.
• McCune–Albright triad: coast of Maine café-au-lait macules, polyostotic fibrous dysplasia, and peripheral precocious puberty from autonomous ovarian cysts — mosaic activating GNAS mutation, constitutive Gsα–cAMP signalling. Contrast with NF1's smooth coast of California borders.
• The GnRH stimulation test settles it: a pubertal LH-predominant rise = central; flat, suppressed LH with high sex steroids = peripheral.
• Classic distractor: giving a GnRH agonist for peripheral disease. It cannot work — the pituitary is already suppressed. Treat the source (glucocorticoid, resection, aromatase inhibitor/antiandrogen).
• The one bone-age exception: severe primary hypothyroidism (Van Wyk–Grumbach) causes precocious puberty with a delayed bone age and poor growth; TSH cross-reacts with the FSH receptor, and levothyroxine is the treatment.
• hCG-secreting tumours virilise boys only — hCG mimics LH at the Leydig cell, but ovarian oestrogen production also needs FSH. Check β-hCG and AFP in a virilised boy with a suppressed LH.
• Always ask about exogenous exposure: a parent's transdermal testosterone or oestrogen gel is a cheap, fully reversible cause.