A 6-year-old boy develops pubic hair (Tanner stage 3), penile enlargement, and testicular volume of 6 mL bilaterally over 6 months. Serum testosterone is elevated for age, but LH and FSH are prepubertal (LH <0.3 IU/L). GnRH stimulation shows no LH rise. Which diagnosis is most likely?

• A Central precocious puberty
• B Familial male-limited precocious puberty (testotoxicosis) ✓
• C Congenital adrenal hyperplasia
• D HCG-secreting germ cell tumor

Explanation

Peripheral (gonadotropin-independent) precocious puberty in a boy with prepubertal LH, elevated testosterone, and asymmetric or enlarged testes points to familial male-limited precocious puberty (testotoxicosis), an activating mutation of the LH receptor causing autonomous testosterone production. Central precocious puberty would show pubertal LH response to GnRH. CAH causes testicular adrenal rest tumors but LH would not be autonomously suppressed with this pattern. HCG-secreting tumors would elevate serum HCG, not LH receptor function.

Reference: Nelson Textbook of Pediatrics, 21st ed.

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