Delayed puberty and hypogonadism in adolescents — branching viva

Opening framework

My framework has four layers. First, the timing — no testicular enlargement (under four millilitres) by 14 in boys or no thelarche by 13 in girls, or a stall of more than two years. Second, the gonadotrophin split — a morning testosterone or oestradiol with FSH and LH divides the differential into a central (hypogonadotropic) and a gonadal (hypergonadotropic) cause. Third, the clock-versus-furnace distinction — constitutional delay is a late but intact clock, permanent CHH is a defective clock, and primary gonadal failure is a clock with no furnace. Fourth, the induction principle — gradual sex-steroid escalation over 18 to 24 months to mimic normal puberty. [1]

The timing and the triad

This 14-year-old boy meets the definition: his testes are three millilitres, below the four-millilitre threshold for pubertal onset. The triad of short stature on the third centile with a mid-parental target on the fortieth, a bone age lagging by two and a half years, and both parents with a history of late puberty points to constitutional delay of growth and puberty — the commonest cause in boys, roughly 60 percent of referrals. His growth velocity is normal, which is reassuring: a falling-off velocity would force me to look beyond constitutional delay. [1]

The gonadotrophin split and the CDGP-versus-CHH problem

The single most discriminating test is the gonadotrophin level. Low or inappropriately normal FSH and LH with a low testosterone confirm a central cause, which is where this boy sits. The harder question is whether his central cause is temporary (CDGP) or permanent (CHH). The features that push toward CHH are anosmia (Kallmann syndrome), a history of micropenis or cryptorchidism at birth reflecting deficient neonatal minipuberty, a standing height that is normal-to-tall rather than short-for-age throughout childhood, and a family history of anosmia or infertility rather than just late puberty. This boy has none of those — his stature is short-for-age, his smell is intact, his neonatal history is unremarkable, and his family history is of late puberty — so constitutional delay is the working diagnosis, with a planned period of watchful waiting to confirm spontaneous progression. [1] [6]

The role of short-course testosterone

If the psychological burden is significant — and for a 14-year-old boy who is the shortest and least mature in his class, it often is — a short course of intramuscular testosterone (50 to 100 milligrams monthly for three to six months) serves two purposes. It induces the early changes of puberty and a growth spurt that relieves the distress, and it is a diagnostic trial: constitutional delay will show a pubertal response that continues after the course stops, whereas CHH will not progress independently. The Stancampiano structured approach emphasises that this is given at a dose and duration that does not advance bone age excessively or compromise final height. [12]

Branch 1: the high-gonadotrophin boy

The second case — a 15-year-old with tall stature, small firm testes, gynaecomastia, and markedly elevated FSH and LH with a low testosterone — is hypergonadotropic hypogonadism, and the phenotype is Klinefelter syndrome (47,XXY), the commonest genetic cause of primary gonadal failure at roughly one in 600 male births. The confirmatory test is a karyotype. The supernumerary X causes dysgenesis of the seminiferous tubules, low testosterone, and loss of feedback with rising gonadotrophins. The associated features are learning and behavioural vulnerabilities, metabolic and cardiovascular risk, osteoporosis, and infertility. [7] [1]

Branch 2: pubertal induction and fertility

Pubertal induction in Klinefelter uses escalating testosterone over 18 to 24 months — low-dose intramuscular or transdermal testosterone started at a fraction of the adult dose and increased gradually, per the Endo-ERN guideline. Rapid escalation is harmful because it advances bone age and compromises final height and because it outpaces psychosocial maturation. Fertility is impaired but micro-dissection testicular sperm extraction can recover sperm in many men, so early semen analysis and cryopreservation counselling are part of the long-term plan. Induction is followed by lifelong replacement and transition to adult endocrine care. [9] [7]