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Case: 13-year-old boy with short stature and delayed puberty
1. Likely Diagnosis: Constitutional Delay of Growth and Puberty (CDGP)
This is the most common cause of delayed puberty in adolescent boys and the second most common cause of short stature overall (after familial short stature).
2. Features That Support CDGP in This Case
| Feature | This Patient | Supports CDGP? |
|---|---|---|
| Age 13, short but height on 5th centile | Present | Yes |
| Normal growth velocity | Present | Yes - growth velocity is normal, just shifted lower |
| Bone age delayed (11 yrs in a 13-yr-old) | Present | Yes - bone age = height age, not chronologic age |
| Prepubertal genitalia (delayed puberty) | Present | Yes |
| Family history - father also "grew late" | Present | Yes - autosomal dominant family pattern |
Key textbook points:
- The bone age equals the height age (the age at which their height would plot on the 50th percentile) - Textbook of Family Medicine 9e
- There is usually a positive family history of delayed growth and puberty - Textbook of Family Medicine 9e
- CDGP children follow a lower percentile until their delayed pubertal growth spurt catches up - Textbook of Family Medicine 9e
- Normal growth velocity is the hallmark distinguishing it from pathologic causes - Harriet Lane Handbook, Table 10.20
3. How CDGP Differs from Growth Hormone (GH) Deficiency
This is the critical differential:
| Feature | CDGP | GH Deficiency |
|---|---|---|
| Growth velocity | Normal | Decreased (key distinction) |
| Bone age | Delayed | Delayed |
| Puberty | Delayed but eventually spontaneous | May be delayed; needs treatment |
| GH levels | Normal | Low (fails stimulation tests) |
| IGF-1 / IGFBP-3 | Normal | Low |
| Adult height | Normal (catches up) | Short (if untreated) |
| Predicted adult height | Near mid-parental height | Below mid-parental height |
| Treatment | Reassurance ± short-course testosterone | Recombinant GH injections required |
From Goodman & Gilman: "Children with GH deficiency present with short stature, delayed bone age, and a low age-adjusted growth velocity." The diagnosis should be considered when height is >2-2.5 SD below normal AND growth velocity is decreased AND predicted adult height is substantially below mid-parental height.
In this boy, growth velocity is explicitly stated to be normal - this argues strongly against GH deficiency and in favor of CDGP.
Also from Swanson's Family Medicine: "Constitutional delay of growth... is manifested by delayed bone age and signs of sexual maturation. Hypothyroidism and growth hormone deficiency are usually manifested with a delayed bone age AND a decreased growth velocity."
4. What Should Be Done
Investigations:
- Wrist X-ray for bone age (already done: 11 years - consistent)
- Height and weight, mid-parental height calculation: [(Father's height + Mother's height - 13 cm) / 2] for boys
- Thyroid function (TFTs) to exclude hypothyroidism
- FBC, ESR, LFTs, renal function - to exclude chronic systemic disease
- LH, FSH, testosterone - typically low/prepubertal but appropriate for bone age
- IGF-1 and IGFBP-3 if GH deficiency is still suspected
- GH stimulation test only if growth velocity is low (not needed here)
Management:
- Reassurance - explain that puberty will occur spontaneously, and final adult height will be normal. The father's history confirms this pattern.
- Regular monitoring - growth charts every 6 months
- Consider short-course low-dose testosterone (e.g., testosterone enanthate 50-100 mg IM monthly for 3-6 months) if psychological distress is significant - this can "kick-start" puberty without compromising final height
- No GH therapy is indicated in CDGP with normal growth velocity
Prognosis: Excellent. These boys eventually enter puberty spontaneously and reach a normal adult height consistent with their genetic potential (mid-parental height target) - Tietz Textbook of Laboratory Medicine, Harriet Lane Handbook
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Case: 8-year-old boy with progressive height faltering, immature facies, and delayed bone age
1. Diagnosis to Consider: Growth Hormone Deficiency (GHD)
This is the most likely diagnosis. The clinical picture is classic:
- Progressive height faltering - falling from 25th to below 3rd centile over 3 years (declining growth velocity)
- Weight preserved on 25th centile - weight is relatively spared compared to height, unlike malnutrition
- Immature facial appearance - characteristic "cherubic" doll-like face with frontal bossing
- Increased subcutaneous fat - especially truncal, due to lack of GH's lipolytic effect
- Normal school performance - rules out hypothyroidism (which causes intellectual impairment) and CNS causes
- Bone age delayed by 3 years - consistent with GHD
Idiopathic GHD is the most common cause of GH deficiency in children. - Henry's Clinical Diagnosis and Management by Laboratory Methods
2. Which Growth Parameter Is Particularly Important?
Growth velocity (the rate of height gain, cm/year) is the single most important parameter.
- In GHD, growth velocity is decreased - the child is actively falling across height centiles (as seen here: 25th → below 3rd over 3 years)
- This is the critical distinction from CDGP, where growth velocity is normal and the child follows a low but parallel centile
- From Goodman & Gilman: "Children with GH deficiency present with short stature, delayed bone age, and a low age-adjusted growth velocity"
- From Harriet Lane Handbook (Table 10.20): Pathologic causes of short stature = decreased growth velocity vs. CDGP and familial short stature = normal growth velocity
A child falling through centiles = pathological. A child running along a low centile = likely constitutional/familial.
3. Investigations to Request
| Investigation | Rationale |
|---|---|
| Bone age (wrist X-ray) | Already done - delayed by 3 years (consistent with GHD) |
| IGF-1 (Insulin-like Growth Factor 1) | Screening test - low in GHD; stable levels, can be taken any time |
| IGFBP-3 | Companion to IGF-1; less nutrition-dependent; but imperfect sensitivity |
| GH stimulation test x2 | Gold standard - definitive diagnosis requires failure to respond to two different stimuli |
| Thyroid function tests (TFTs) | Hypothyroidism causes similar picture (delayed bone age + slow growth) - must exclude first |
| Full blood count, ESR, renal/liver function | Exclude chronic systemic disease |
| MRI pituitary/hypothalamus | Essential once GHD confirmed biochemically - exclude craniopharyngioma or structural defect |
| Karyotype | If Turner syndrome (46,XX) is a differential (less relevant in a boy) |
Screening pathway:
- If IGF-1 is within normal range for age/sex → GHD excluded
- If IGF-1 is low → proceed to formal GH stimulation testing
- Tietz: "If IGF-I is squarely within its reference interval for age and sex in children, GH deficiency is excluded. If IGF-I is low, definitive GH testing is required."
GH stimulation tests used in children:
- Insulin tolerance test (ITT) - gold standard but unpleasant; less used in children
- Arginine stimulation test - preferred in children
- Glucagon stimulation test - widely used alternative
- Clonidine, L-dopa - other pharmacologic stimuli
- Cut-off: GH failing to rise above 10 ng/mL in children = abnormal (vs. 3-5 ng/mL in adults)
- Classical pediatric diagnosis requires two separate stimulation tests both showing deficient GH response
4. Why Is a Random GH Level Not Useful?
GH is secreted in pulses - it is released episodically, primarily during deep sleep (stages III/IV) and after exercise. Between pulses, GH levels are very low or undetectable.
- In healthy normal individuals, approximately 80% of random GH results are below 1 ng/mL - indistinguishable from a GH-deficient child
- A single low random GH level therefore cannot diagnose GHD because it may simply reflect the trough between normal secretory pulses
- A single normal random GH level does not exclude GHD either
- Henry's: "No simple reproducible method for determining abnormal GH secretory patterns exists... typically 80% of GH results are below 1 ng/mL in healthy normal individuals, and secretory peaks reach 20-40 ng/mL"
This is why pharmacological stimulation tests are required - they bypass the pulsatile nature of GH secretion and provoke a maximal GH response, making the test reproducible and diagnostically valid.
Summary of management once confirmed:
- Recombinant human GH (rhGH) therapy - daily subcutaneous injections
- Regular monitoring of growth velocity and IGF-1 levels on treatment
- MRI pituitary to identify structural cause
- Screen for other pituitary hormone deficiencies (TSH, ACTH, ADH axes)
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