In a 6‑year‑old boy with precocious puberty and suppressed basal follicle‑stimulating hormone (FSH) and luteinizing hormone (LH), does this indicate that his bone age is stable and not advancing?

Suppressed FSH and LH in Precocious Puberty: Bone Age Control

No—suppressed basal FSH and LH in a 6-year-old boy with precocious puberty does NOT indicate that bone age is under control; rather, it indicates successful suppression of the hypothalamic-pituitary-gonadal axis by GnRH analog therapy, but bone age advancement must be monitored separately through serial radiographic assessment.

Understanding the Hormonal Suppression

Suppressed gonadotropins reflect treatment efficacy, not bone age status:

• When GnRH analogs are used to treat central precocious puberty, basal LH and FSH levels decrease within 1 week of initiating therapy, and sex steroid secretion decreases within 2 weeks to prepubertal range 1
• The suppression of FSH and LH indicates that the GnRH pulse generator has been successfully downregulated by continuous GnRH analog stimulation, which desensitizes gonadotrophs and reduces gonadotropin release 2
• This hormonal suppression is the mechanism of treatment, not a marker of bone age control 1

Bone Age Monitoring Requirements

Bone age must be assessed independently through serial radiographs:

• The velocity of skeletal maturation decreases after 12 months of GnRH analog therapy and is sustained during continued therapy over 18-36 months, but this requires direct measurement 1
• Bone age X-rays should be obtained at baseline and serially during treatment to assess skeletal maturation and predict impact on final height 2
• Delayed bone age and joint pain are common signs of GH excess in children, but in precocious puberty, accelerated bone maturation is the concern—treatment aims to slow this progression 3

Treatment Monitoring Algorithm

To determine if bone age is truly "under control," you must:

1. Verify hormonal suppression (which you have):

   • Basal LH and FSH should be suppressed to prepubertal levels 1
   • Sex steroids (testosterone in boys) should be in prepubertal range 1

2. Assess clinical response:

   • Secondary sexual characteristics should cease advancing or revert toward prepubertal state 1
   • Height velocity should decrease during therapy 1

3. Monitor skeletal maturation directly:

   • Obtain bone age X-rays every 6-12 months during treatment 2
   • Calculate the ratio of bone age advancement to chronological age advancement
   • Bone age is "under control" when the rate of skeletal maturation slows to approximately 1 year per chronological year 1

Common Pitfall to Avoid

Do not assume suppressed gonadotropins equal controlled bone age:

• Some patients may have a subnormal growth rate (less than 4.5 cm/year) during GnRH analog therapy, indicating over-suppression, while others may continue to have accelerated skeletal maturation despite hormonal suppression 1
• The velocity of skeletal maturation must be directly measured—it cannot be inferred from hormone levels alone 1
• In boys with central precocious puberty, serum inhibin B might result from the contribution of Sertoli cell mass even when FSH is suppressed, highlighting that hormonal markers don't always correlate perfectly with tissue-level changes 4

Additional Monitoring Considerations

Beyond bone age, assess:

• Height velocity and standard deviations above mean height for age, which should decrease during therapy 1
• Testicular volume, which should stabilize or decrease 4
• Growth velocity more than +2 SDS or abnormally tall stature defined as +2 or +3 SDS above country-specific, age-appropriate and sex-appropriate mean height indicates inadequate control 3