Clinical Scenario:
A 5-year-old girl is brought to the clinic because of progressive breast development and the recent appearance of pubic hair over the past 6 months. Her growth chart shows a marked acceleration in height velocity, with her height percentile increasing from the 50th to the 90th percentile. Examination reveals Tanner stage III breast development and Tanner stage II pubic hair. There are no café-au-lait skin lesions, headaches, visual abnormalities, or other neurological findings.
A left hand and wrist radiograph shows advanced skeletal maturation, with a bone age of 8 years. A GnRH stimulation test produces a pubertal LH response, with a peak LH concentration of 8.5 mIU/mL. Pelvic ultrasonography demonstrates pubertal changes in the uterus and ovaries.
What is the most likely underlying mechanism responsible for this presentation?
A. Autonomous estrogen secretion from an ovarian lesion
B. Exogenous estrogen exposure
C. Premature activation of the hypothalamic-pituitary-gonadal (HPG) axis
D. Androgen excess due to non-classic congenital adrenal hyperplasia
E. Autonomous gonadal activation associated with McCune-Albright syndrome
Correct answer & Explanation:
Correct answer: C. Premature activation of the hypothalamic-pituitary-gonadal (HPG) axis
Explanation
This child has central precocious puberty (CPP), caused by premature activation of the hypothalamic-pituitary-gonadal axis.
The important clues are:
- Progressive breast development before 8 years of age
- Rapid growth acceleration
- Advanced bone age
- Pubertal progression involving both gonadarche and adrenarche
- Pubertal LH response following GnRH stimulation
- Pubertal uterine and ovarian maturation on ultrasound
In central precocious puberty, premature pulsatile secretion of GnRH from the hypothalamus stimulates the pituitary to release LH and FSH. These gonadotropins stimulate the ovaries, resulting in increased estrogen production and progressive breast and reproductive tract maturation.
The pubertal LH response is particularly important. In GnRH-dependent precocious puberty, stimulated LH becomes pubertal, whereas peripheral causes of precocious puberty generally produce sex-steroid effects without activation of the HPG axis and therefore have a prepubertal gonadotropin response.
Why the other options are less likely
A. Autonomous estrogen secretion from an ovarian lesion — Incorrect
An ovarian cyst or estrogen-secreting ovarian lesion can produce breast development and other estrogen effects, but this is a GnRH-independent (peripheral) mechanism. The gonadotropin response would generally remain prepubertal.
B. Exogenous estrogen exposure — Incorrect
External estrogen can cause breast development and other estrogenic effects without activating the HPG axis. It would not explain the clearly pubertal LH response.
D. Non-classic congenital adrenal hyperplasia — Incorrect
Non-classic CAH causes excess adrenal androgens, typically presenting with premature pubic/axillary hair, acne, or virilization. It does not explain progressive breast development with a pubertal LH response.
E. McCune-Albright syndrome — Incorrect
McCune-Albright syndrome can cause peripheral precocious puberty, particularly recurrent estrogen-producing ovarian cysts in girls. Café-au-lait pigmentation may be present, although its absence does not completely exclude the syndrome. The key point here is that the pubertal GnRH-stimulated LH response indicates central rather than peripheral activation.
Exam Pearl
Pubertal LH response after GnRH stimulation + advanced bone age + progressive secondary sexual characteristics = central precocious puberty.
The 2026 Endocrine Society guideline defines central precocious puberty as premature activation of the HPG axis, traditionally resulting in pubertal development before age 8 in girls and before age 9 in boys.
You can also view High-Yield Exam Summary on Precocious Puberty
References:
- Endocrine Society. Central Precocious Puberty: An Endocrine Society Clinical Practice Guideline. 2026.
- Kliegman RM, St Geme JW, Blum NJ, Shah SS, Tasker RC, Wilson KM, editors. Nelson Textbook of Pediatrics. 22nd ed. Philadelphia: Elsevier; 2025.
