A 6-year-old girl is brought to the pediatrician by her father for an annual physical examination. The father reports that the patient is a happy and healthy child, but he sometimes worries about her weight. He says that she is a “picky” eater and only wants chicken nuggets and French fries. He also notes some mild acne on her cheeks and forehead but thinks it’s because she “doesn’t like baths.” The father says she has met all her pediatric milestones. She has recently started kindergarten, can tell time, and is beginning to read. Her teacher says she gets along with her classmates well. The patient was born at 38 weeks gestation. She has no chronic medical conditions and takes only a multivitamin. Height and weight are above the 95th percentile. Physical examination reveals scattered comedones on the patient’s forehead and bilateral cheeks. There is palpable breast tissue bilaterally with raised and enlarged areolae. Scant axillary hair and coarse pubic hair are also noted. A radiograph of the left hand shows a bone age of 9 years. Serum follicular stimulating hormone (FSH) level is 9.6 mU/mL (normal range 0.7-5.3 mU/mL) and luteinizing hormone (LH) level is 6.4 mU/mL (normal range < 0.26 mU/mL). Which of the following is the most appropriate diagnostic test?

Brain magnetic resonance imaging (MRI)

Dehydroepiandrosterone sulfate levels

A 6-year-old boy is brought to the physician by his mother who is concerned about his early sexual development. He has no history of serious illness and takes no medications. He is at the 99th percentile for height and 70th percentile for weight. His blood pressure is 115/78 mm Hg. Examination shows greasy facial skin and cystic acne on his forehead and back. There is coarse axillary and pubic hair. Serum studies show: Cortisol (0800 h) 4 μg/dL Deoxycorticosterone 2.5 ng/dL (N = 3.5–11.5) Dehydroepiandrosterone sulfate 468 mcg/dL (N = 29–412) Which of the following is the most likely underlying cause of this patient's symptoms?

Idiopathic overproduction of GnRH

Constitutive activation of adenylyl cyclase

A 7-year-old girl is brought to the physician because of vaginal bleeding for 2 days. There is no personal or family history of serious illness. She is at the 95th percentile for height and at the 90th percentile for weight. Examination shows enlarged breasts, and the areola and papilla have formed a secondary mound. There is coarse pubic hair that does not extend to the inner thigh. The remainder of the examination show no abnormalities. An x-ray of the left hand and wrist shows a bone age of 11 years. Her serum luteinizing hormone concentration is 0.1 mIU/mL (N < 0.2 mIU/mL). Which of the following is the most appropriate next step in management?

Serum dehydroepiandrosterone level

A 3-year-old girl is brought to the physician by her parents for complaints of breast development and pubic hair growth for the past 6 months. She has no significant birth or medical history. The temperature is 37.0°C (98.6°F), the pulse is 88/min, and the respirations are 20/min. Physical examination shows enlarged breasts at Tanner stage 3 and pubic hair at stage 2. Height and weight are in the normal range. On GnRH stimulation testing, a luteinizing hormone (LH) response of < 5 IU/L is detected. What is the most appropriate next step in diagnosis?

Measure baseline estradiol levels and perform pelvic ultrasound

Perform leuprolide stimulation test to measure testosterone

Measure FSH levels to evaluate pituitary function

Calculate LH:FSH ratio from previous GnRH test

Repeat GnRH stimulation test to confirm LH response

Precocious puberty for USMLE Step 2 CK: High-Yield Pediatrics Lessons

Definition & Cutoffs - Too Fast, Too Young

Definition: Onset of secondary sexual characteristics (SSCs) before the accepted lower age limit.
Age Cutoffs:
- Girls: < 8 years
- Boys: < 9 years
Classification:
- Central (True/GnRH-dependent): Premature activation of the hypothalamic-pituitary-gonadal (HPG) axis.
- Peripheral (Pseudo/GnRH-independent): Excess sex hormones from gonads, adrenals, or exogenous sources.

⭐ The most common form of precocious puberty is idiopathic Central Precocious Puberty (CPP), and it is much more frequent in girls (approx. 10:1 girl-to-boy ratio).

Classification - Brain vs. Body Hormones

Central (GnRH-dependent): True, complete puberty from premature activation of the Hypothalamic-Pituitary-Gonadal (HPG) axis.
Peripheral (GnRH-independent): Pseudopuberty from sex hormones produced outside the brain/pituitary control loop (e.g., adrenals, gonads, external sources).

Hypothalamic-Pituitary Axis and Target Organs

⭐ While Central Precocious Puberty (CPP) is most often idiopathic in girls, a boy with CPP has a much higher likelihood of an underlying CNS lesion, mandating a brain MRI.

📌 Mnemonic: Central = CNS problem. Peripheral = Problem in the Physique (gonads/adrenals).

Diagnostic Workup - The Hormone Hunt

Initial Steps:
- Bone Age: First-line investigation. X-ray of the left hand and wrist. Bone age is typically advanced >2 years beyond chronological age.
- Hormonal Assay: Basal LH, FSH, estradiol (girls) or testosterone (boys). A basal LH > 0.3 IU/L is highly suggestive of Central Precocious Puberty (CPP).
Confirmatory Test:
- GnRH Stimulation Test: The gold standard to differentiate CPP from Peripheral Precocious Puberty (PPP).
- Pubertal Response (CPP): Peak LH > 5-8 IU/L and a peak LH/FSH ratio > 0.66.

⭐ The GnRH stimulation test is the definitive investigation to differentiate between GnRH-dependent (central) and GnRH-independent (peripheral) precocious puberty.

Algorithm for diagnosing precocious puberty in boys

Management - Pumping the Brakes

Central (CPP): Goal is to ↓ GnRH pulses & preserve adult height.

DOC: Long-acting GnRH analogs (continuous stimulation → downregulation).
- Leuprolide acetate (monthly/3-monthly depot).
- Triptorelin, Histrelin implant.
Monitor: ↓ Growth velocity & slowing of bone age advancement.

Peripheral (PPP): Address the specific underlying cause.

McCune-Albright: Aromatase inhibitors (Letrozole).
Testotoxicosis: Anti-androgens + Aromatase inhibitors.

⭐ GnRH agonist therapy initially causes a transient flare-up of puberty (↑ LH/FSH) before downregulation and suppression.

High-Yield Points - ⚡ Biggest Takeaways

Secondary sexual characteristics before age 8 in girls & 9 in boys.

Central (GnRH-dependent) shows a pubertal LH response to GnRH stimulation; peripheral (GnRH-independent) does not.

The first investigation is bone age assessment, which is typically advanced.

Central form is mostly idiopathic in girls; suspect CNS pathology in boys.

Key peripheral causes include McCune-Albright syndrome and adrenal or gonadal tumors.

Treatment for the central form is GnRH agonists (e.g., Leuprolide).

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