Overview & Definition

• Definition: Absence of testicular enlargement (volume < 4 mL or length < 2.5 cm) by 14 years of age.
• Alternate Definition: Lack of pubertal changes 2 to 2.5 Standard Deviations (SD) later than population mean.
• Epidemiology: More common in boys than girls.
• Key Nuance: Presence of pubic hair (adrenarche) does not exclude delayed puberty (gonadarche).

Etiological Classification

Detailed Etiology & Pathophysiology

Constitutional Delay of Growth and Puberty (CDGP)

• Pathogenesis: Extreme variation of normal pubertal timing. Delayed maturation of HPG axis.
• Genetics: Highly heritable. 50-75% report family history of delayed puberty. Inheritance patterns include autosomal dominant, autosomal recessive, X-linked, and bilineal.
• Molecular Defects: Mutations in IGSF10 cause delayed migration of GnRH neurons from olfactory bulbs to hypothalamus during embryogenesis. LIN28B variants also implicated.
• Growth Pattern: Normal birth size. Growth deceleration between 6 months and 2 years. Tracks along lower percentiles. Delayed skeletal maturation (bone age).
• Clinical Course: Endogenous puberty eventually occurs. Adult height usually reaches genetic target range, though pubertal growth spurt magnitude may be diminished.

Functional (Transient) Hypogonadotropic Hypogonadism

• Pathogenesis: Adaptive suppression of HPG axis to conserve energy during chronic stress or negative energy balance.
• Nutritional: Anorexia nervosa, malnutrition.
• Systemic Illness: Celiac disease, inflammatory bowel disease, cystic fibrosis, chronic renal failure, sickle cell anemia, thalassemia.
• Endocrine: Hypothyroidism, poorly controlled diabetes mellitus, hyperprolactinemia.
• Excessive Exercise: Elite athletes, wrestlers ("making weight").

Persistent Hypogonadotropic Hypogonadism (HH)

Characterized by low LH, low FSH, and low testosterone.

Kallmann Syndrome & Normosmic HH

• Kallmann Syndrome (KS): HH combined with anosmia/hyposmia. Defective GnRH neuronal migration from olfactory placode.
• Genetics: ANOS1 (KAL1) (X-linked). FGFR1, PROK2, PROKR2, FGF8, CHD7, NSMF.
• Isolated/Normosmic HH: GNRHR, GNRH1, KISS1R (encodes kisspeptin receptor), TAC3 (neurokinin B), TACR3.
• Reversibility: ~10% of IHH cases achieve normal reproductive endocrine activity in adulthood despite carrying loss-of-function mutations (e.g., FGFR1, TAC3).

Multiple Pituitary Hormone Deficiencies (MPHD)

• Transcription Factor Defects: Mutations in PROP1, HESX1, LHX3, LHX4, SOX3 cause multiple pituitary hormone deficiencies including HH. PROP1 mutations may present with late-onset HH.
• Congenital Malformations: Holoprosencephaly, septo-optic dysplasia.

Syndromic HH

• Prader-Willi Syndrome: HH + hyperphagia + obesity. Involves both hypothalamic dysfunction and primary testicular dysfunction.
• Adrenal Hypoplasia Congenita (AHC): X-linked mutation in NR0B1 (DAX1). Fetal adrenal cortex normal, adult zone fails to develop. HH presents in adolescence.
• Other Syndromes: Bardet-Biedl, Alström, Laurence-Moon.
• Genetic Obesity: Leptin (LEP), Leptin receptor (LEPR), PCSK1 mutations cause obesity and HH.

Acquired HH

• Tumors: Craniopharyngioma, glioma, germinoma, pituitary adenoma (prolactinoma).
• Infiltrative: Langerhans cell histiocytosis, hemochromatosis, sarcoidosis.
• Iatrogenic: Cranial radiation, neurosurgery, chronic glucocorticoids, opiates.

Hypergonadotropic Hypogonadism (Primary Testicular Failure)

Characterized by elevated LH and FSH, low testosterone.

Klinefelter Syndrome (47,XXY)

• Incidence: 1 in 500 to 667 males.
• Pathophysiology: Prepubertal testes relatively normal. Puberty onset initiates massive germ cell apoptosis, seminiferous tubule hyalinization, and fibrosis.
• Clinical Features: Small firm testes (<5 mL), tall stature (eunuchoid habitus), microphallus, gynecomastia (50-80%), learning disabilities.
• Height Mechanism: Extra copy of SHOX gene on pseudoautosomal region of X chromosome causes tall stature.

Other Primary Testicular Defects

• Congenital Anorchia (Vanishing Testes Syndrome): 46,XY males with normal external genitalia but absent testes. Suggests testicular loss between 14th week and birth. Undetectable Anti-Müllerian Hormone (AMH), absent testosterone response to hCG.
• Acquired Damage: Chemotherapy (alkylating agents, platinum), testicular radiation, bilateral torsion, mumps orchitis, trauma.
• Steroidogenic Defects: 5a-reductase deficiency, 17,20-lyase deficiency, 17b-HSD3 deficiency.
• Testicular Dysgenesis Syndrome: Environmental endocrine disruptors (phthalates, bisphenol A) linked to cryptorchidism, hypospadias, low sperm count.

Clinical Evaluation

Medical History

• Growth Pattern: Review prior height/weight records. Growth deceleration <3 cm/year suggests specific disease.
• Systemic Symptoms: GI distress (Celiac/IBD), headache/visual changes (CNS tumor), anosmia/hyposmia (Kallmann).
• Neonatal History: Micropenis or cryptorchidism at birth suggests congenital HH. Prolonged jaundice, hypoglycemia suggests hypopituitarism.
• Family History: Parental pubertal timing, heights, infertility. Self-limited DP in parent strongly suggests CDGP.

Physical Examination

• Anthropometry: Calculate growth velocity. Measure upper-to-lower segment ratio and arm span. Arm span >5 cm greater than height indicates eunuchoid habitus (hypogonadism). Underweight suggests chronic illness/eating disorder; obesity suggests specific genetic syndromes (LEPR, PCSK1, Prader-Willi).
• Genital Examination:
  • Testicular Volume: Use Prader orchidometer. Volume $\ge$ 4 mL indicates onset of central puberty.
  • Penile Length: Assess stretched penile length. Micropenis indicates inadequate prenatal testosterone.
  • Scrotum: Check for cryptorchidism, bifid scrotum, hypospadias.
• Secondary Sex Characteristics: Differentiate Tanner genital stage from pubic hair stage.
• General Exam: Neurologic/visual field exam, olfactory testing (sense of smell), dysmorphic features.

graph TD

Start["Boy ≥ 14 years with no testicular enlargement (volume < 4 mL)"] --> Eval["1\. Clinical Evaluation: History (Growth, Family Hx) & Physical Exam"]

Eval --> FirstLine["2\. First-Line Labs: Bone Age, Basal LH & FSH, Testosterone, Systemic Screen (TSH, etc.)"]

FirstLine --> LHFSH{"Basal LH & FSH Levels"}

%% Hypergonadotropic Branch
LHFSH -- "High (Elevated)" --> Hyper["Hypergonadotropic Hypogonadism (Primary Testicular Failure)"]
Hyper --> Karyotype["Check Karyotype (Mandatory to rule out Klinefelter 47,XXY)"]
HyperTx["Management: Testosterone Replacement, Fertility Preservation"]
Karyotype --> HyperTx

%% Hypogonadotropic Branch
LHFSH -- "Low / Normal" --> Hypo["Secondary Hypogonadism"]
Hypo --> Screen{"Systemic / Chronic Illness Present?"}

Screen -- "Yes" --> FHH["Functional HH (e.g., Celiac, Anorexia, Hypothyroidism)"]
FHH --> FHHTx["Management: Treat Underlying Condition"]

Screen -- "No" --> CDGP_vs_HH["Differentiate: CDGP vs. Persistent HH"]
CDGP_vs_HH --> SecondLine["Second-Line Labs<br/>Inhibin B, GnRH/hCG Stim Tests, MRI, Olfactory Test"]

%% Differentiating CDGP and PHH
SecondLine --> CDGP["Constitutional Delay of Growth & Puberty (CDGP)<br/>(e.g., Inhibin B &gt; 65 pg/mL, Family Hx)"]
CDGP --> CDGPTx["Management: Watchful Waiting OR Short-course Low-Dose Testosterone"]

SecondLine --> PHH["Persistent HH (e.g., Kallmann Syndrome, MPHD)<br/>(e.g., Inhibin B &lt; 35 pg/mL, Anosmia, MRI findings)"]
PHH --> PHHTx["Management: Long-term Testosterone, Exogenous Gonadotropins for Fertility"]

Diagnostic Investigations

First-Line Investigations

Second-Line Investigations (Differentiating CDGP vs. HH)

Management & Therapeutics

1. Constitutional Delay of Growth and Puberty (CDGP)

• Watchful Waiting: Observation with reassurance is appropriate if psychosocial distress is minimal.
• Low-Dose Testosterone Therapy:
  • Indication: Psychosocial distress, bullying, severe anxiety over lack of growth/development.
  • Regimen: Testosterone enanthate or cypionate 50-100 mg Intramuscularly (IM) every 4 weeks for 3 to 6 months.
  • Goal: Induces secondary sexual characteristics, promotes growth spurt, jump-starts endogenous puberty without unduly advancing bone age or compromising adult height.
  • Follow-up: Halt after 3-6 months. Reassess endogenous testosterone and testicular volume. If spontaneous puberty does not resume, consider second course or re-evaluate for HH.
• Alternative (Experimental) Therapies:
  • Aromatase Inhibitors (Letrozole/Anastrozole): Delays epiphyseal fusion by blocking estrogen synthesis. May increase final adult height, but safety concerns (vertebral deformities, altered spermatogenesis) limit routine use; FDA non-approved.
  • Anabolic Steroids: Oxandrolone (1.25-2.5 mg/day PO). Weak androgenic effect; carries hepatotoxicity risk. Rarely used.

2. Persistent Hypogonadotropic Hypogonadism (HH)

• Testosterone Replacement (Virilization):
  • Initiation: Can begin around age 12-14.
  • Escalation: Start at 50 mg IM every 4 weeks. Increase by 50 mg increments every 6-12 months over 3 years.
  • Adult Maintenance: 100-200 mg IM every 2 weeks, or daily transdermal testosterone gel (1%).
  • Limitation: Exogenous testosterone does not induce testicular growth or spermatogenesis.
• Fertility Induction (Spermatogenesis):
  • Regimen: Requires exogenous gonadotropins. hCG (500-3000 IU 2-3x/week) + Recombinant human FSH (75-225 IU 2-3x/week) administered Subcutaneously (SC).
  • Pulsatile GnRH: Delivered via SC pump (if pituitary intact). Most physiologic, but highly complex.

3. Hypergonadotropic Hypogonadism (e.g., Klinefelter Syndrome)

• Testosterone Replacement: Initiate when LH/FSH rise above normal and testosterone falls. Titrate to adult dosing (e.g., 200-250 mg every 3-4 weeks IM or transdermal gel).
• Fertility Preservation: Sperm counts decline rapidly during puberty in Klinefelter syndrome. Consider sperm banking in early puberty. Adult paternity achievable via micro-dissection Testicular Sperm Extraction (microTESE) coupled with Intracytoplasmic Sperm Injection (ICSI).
• Gynecomastia Management: Aromatase inhibitors largely ineffective. Surgical reduction often required for severe psychosocial distress.
• Comorbidity Screening: Monitor fasting glucose, lipids, HbA1c, and bone mineral density (increased risk for metabolic syndrome and osteopenia).

Prognosis & Long-Term Consequences

• Adult Height: CDGP adult height may be slightly below genetic target, but generally normal.
• Bone Health: Late pubertal timing directly causes decreased peak Bone Mineral Density (BMD) in adulthood, increasing long-term osteopenia risk.
• Psychosocial: Untreated significant delay correlates with transient academic and emotional difficulties.