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48. How to evaluate a boy with precocious puberty?

In a boy with appearance of secondary sexual characteristics below 9 years of

age, basal serum LH, testosterone, and LH response to GnRH should be per-

formed. Basal LH ≥0.3 IU/L (ICMA) and testosterone >1.7 nmol/L (RIA) sug-

gest a diagnosis of GDPP in boys. Peak LH >5.0 IU/L at 3h, after subcutaneous

administration of aqueous leuprolide (20 μg/Kg), has a sensitivity and specific-

ity of 83 % and 97 %, respectively, for the diagnosis of GDPP in boys. Further

tests are required to establish the etiological diagnosis of precocious puberty

including MR brain imaging or CT abdomen. An approach to a boy with preco-

cious puberty is summarized in the algorithm given below (Fig. 6.12).

49. Why is LH, but not FSH response to GnRH, used for the diagnosis of GDPP?

FSH response to GnRH is present at all ages irrespective of reactivation of

HPG-axis, while LH response to GnRH is present only after reactivation of

HPG-axis. Therefore, rise in LH, but not FSH, reflects the onset of GnRH pulse

generator activity. This is because of stringent neuroendocrine regulation of LH

as compared to FSH at the level of hypothalamus, which is mediated by opioids,

GABA, and dopamine. Hence, in clinical practice, basal and stimulated LH is

estimated to establish the diagnosis of GDPP.

Appearance of Secondary Sexual Characteristics in a boy <9 yrs

Penile enlargement with

testicular volume <3ml

GIPP

↑170HP ↑DHEAS

CAH Adrenal tumor

Exogenous

androgen

exposure

↑ LH, ↑T

GDPP

↓LH, ↑T

• Testotoxicosis


• hCG secreting
  tumor


• MAS

↓LH, ↓ T

Primary

hypothyroidism

Penile enlargement with testicular

volume ≥3ml

Symmetrical

testicular

enlargement

Asymmetrical

testicular

enlargement

↓LH, ↑T

↓LH, ↑T

• CAH with TART


• Leydig cell tumor


• MAS

Fig. 6.12 Approach to a boy with precocious puberty

6 Precocious Puberty