Congenital Hypothyroidism: Clinical Case Discussion & Key Points
Model Case Presentation
Patient Demographics
Name: Baby Meera, Age: 6 weeks, Gender: Female, Informant: Mother (Reliable)
Chief Complaints
- Excessive sleepiness and poor feeding since birth
- Prolonged jaundice – 6 weeks
- Constipation and abdominal distension – 4 weeks
History Summary
Baby has been excessively sleepy since birth, rarely cries, and has a hoarse, weak cry when she does. Feeds poorly — takes a long time, sucks weakly, and falls asleep at the breast. Mother reports the baby feels cold to touch and sweats very little. Constipation since birth (stool once in 3–4 days, hard). Jaundice noted at birth persisted beyond 3 weeks. No vomiting, no seizures. Passed meconium within 48 hours. No family history of thyroid disease. Antenatal period uneventful; no antithyroid medications taken by the mother. Born at term via NVD; birth weight 3.2 kg. Non-consanguineous parents. No newborn screening was performed.
Examination Summary
| Parameter | Finding | Significance |
|---|---|---|
| Weight | 3.5 kg (at 6 weeks) | Poor weight gain — expected ~4.5 kg |
| Length | 52 cm | Short — growth retardation |
| Temperature | 36.0°C | Hypothermia |
| HR | 98/min | Bradycardia for age |
| Jaundice | Present | Prolonged neonatal jaundice (>3 weeks) |
| SpO2 | 98% | Normal |
General appearance: Pale, puffy face, periorbital puffiness, large tongue (macroglossia), wide open anterior fontanelle (4 × 4 cm) and posterior fontanelle (1 × 1 cm).
Skin: Dry, thick, cold, mottled. Carotenemia may be noted (yellow-orange tinge). No goiter palpable (athyreosis/ectopia).
Abdomen: Distended. Umbilical hernia present. Liver and spleen not enlarged.
CNS: Hypotonia. Sluggish Moro reflex. Delayed relaxation of deep tendon reflexes. Lethargy.
Thyroid: Not palpable (consistent with thyroid agenesis or ectopia). Note: Goiter would suggest dyshormonogenesis.
✅ Complete Diagnosis
Congenital Hypothyroidism (Primary, Permanent) — likely due to Thyroid Dysgenesis (Athyreosis), presenting with classical features: prolonged jaundice, hypothermia, macroglossia, large fontanelles, umbilical hernia, hypotonia, constipation, and poor weight gain. Not detected by newborn screening (NBS not done).
📝 History — Exam Q&A
Congenital hypothyroidism (CH) is defined as thyroid hormone deficiency present at birth, resulting in inadequate thyroid hormone production for normal growth and neurodevelopment.
- Worldwide incidence: 1 in 2,000–4,000 live births
- India (non-endemic areas): ~1 in 1,031 term neonates (higher than worldwide average)
- India (iodine-endemic areas): Up to 1 in 13 neonates
- Female predominance: F:M = 2:1
- It is the most common preventable cause of intellectual disability in children
- It is the most common pediatric endocrine disorder
Based on level of defect:
| Type | Defect | TSH | T4 |
|---|---|---|---|
| Primary CH (most common, ~95%) | Thyroid gland itself | ↑↑ | ↓ |
| Central/Secondary CH (~5%) | Pituitary (TSH deficiency) | ↓ or normal | ↓ |
| Tertiary CH (rare) | Hypothalamus (TRH deficiency) | ↓ or normal | ↓ |
| Peripheral CH (rare) | Thyroid hormone resistance/transport defect | ↑ | ↑ or normal |
Primary CH — based on etiology:
| Etiology | Goiter | Permanence | Frequency |
|---|---|---|---|
| Thyroid Dysgenesis (agenesis, ectopia, hypoplasia) | Absent | Permanent | ~80–85% globally; ~57% in India |
| Dyshormonogenesis (enzyme defects in T4 synthesis) | Present | Permanent | ~15–20% globally; ~39% in India (higher in South India) |
| Transient CH (iodine, maternal antibodies, drugs) | Variable | Transient | ~14% in India |
💡 India Difference
Globally, thyroid dysgenesis causes ~80–85% of CH. In India, dyshormonogenesis is proportionally higher (~39%), especially in South India due to consanguineous marriages and iodine deficiency — an important exam point.
Thyroid Dysgenesis (sporadic in 95–98%; genetic in 2–5%):
- Agenesis (athyreosis): Complete absence — most severe form. Genes: TSHR, PAX8, NKX2-1, FOXE1
- Ectopic thyroid: Most commonly at the base of the tongue (lingual thyroid) or along the thyroglossal duct path — most common ectopia
- Hypoplasia: Small gland in normal location
Dyshormonogenesis (autosomal recessive; goiter present):
- TPO gene mutation — defect in iodine organification (most common dyshormonogenesis)
- DUOX2/DUOXA2 — oxidase defect
- SLC5A5 (NIS) — sodium-iodide symporter defect (iodine transport defect)
- TG gene — thyroglobulin synthesis defect
- SLC26A4 (Pendrin) — Pendred syndrome: goitrous CH + sensorineural deafness
- IYD (DEHAL1) — iodotyrosine deiodinase defect
- Iodine deficiency — most common worldwide cause of transient CH and goitrous CH
- Iodine excess — neonatal exposure to iodine-containing antiseptics, contrast dyes (Wolff-Chaikoff effect)
- Maternal TSH receptor-blocking antibodies (TRAb) — cross the placenta; most commonly in mothers with Hashimoto's thyroiditis or Graves' disease treated with surgery
- Maternal antithyroid drugs — PTU or carbimazole taken during pregnancy cross the placenta
- Prematurity/Low birth weight — hypothalamic-pituitary immaturity causing delayed TSH rise
Most CH neonates (>95%) appear normal at birth because:
- Maternal thyroxine transfer: ~25–50% of fetal T4 comes from mother transplacentally, partially protecting the fetus/neonate from the effects of thyroid hormone deficiency
- Partial thyroid function: Many cases (ectopic, hypoplastic, partial dyshormonogenesis) have some residual thyroid function at birth
- Delayed clinical manifestation: Classic features develop over 4–6 weeks as maternal T4 is cleared and thyroid-dependent processes deteriorate
This is why newborn screening is critical — only ~5% of CH infants are detected on clinical grounds alone before biochemical confirmation.
Early features (first 4–6 weeks, if untreated):
- Prolonged physiological jaundice (>3 weeks in term, >4 weeks in preterm) — due to decreased conjugation enzyme activity and prolonged fetal hemoglobin
- Lethargy, excessive sleeping, hypoactivity
- Feeding difficulty — weak suck, slow feeding
- Constipation
- Hypothermia — cold, mottled skin
- Hoarse cry (weak, low-pitched)
- Large anterior and posterior fontanelles
- Hypotonia
Cretinism is the clinical syndrome of untreated severe congenital hypothyroidism. Features appear after 6 weeks:
| System | Features |
|---|---|
| Facies | Coarse facies, puffy eyelids, depressed nasal bridge, wide-set eyes (hypertelorism), broad flat nose, thick lips |
| Tongue | Large (macroglossia) — protrudes out |
| Skin | Dry, rough, thick, cold, pale or mottled; myxedema (non-pitting edema due to mucopolysaccharide deposition) |
| Hair | Coarse, scanty, brittle; low hair line |
| Voice | Hoarse cry |
| Abdomen | Pot-belly abdomen, umbilical hernia, constipation |
| Neurological | Intellectual disability (most severe consequence), hypotonia, delayed milestones, hearing impairment (~10%) |
| Growth | Short stature, delayed bone age, delayed dentition |
| Cardiac | Bradycardia, pericardial effusion (rare) |
| Thyroid | Goiter if dyshormonogenesis; no goiter if dysgenesis |
- Was newborn screening done? — Most important question; CH is a screened disorder
- Prolonged jaundice? — Key early clue; >3 weeks in term baby should prompt thyroid function tests
- Feeding difficulty, hoarse cry, excessive sleep? — Early symptoms
- Constipation? — Common symptom
- Maternal history: Thyroid disorder (Hashimoto's, Graves')? Antithyroid medications (PTU/carbimazole) during pregnancy?
- Maternal iodine exposure: Iodine contrast during pregnancy? Povidone-iodine use in delivery (transient CH)
- Family history: Goiter, thyroid disease, deafness (Pendred syndrome), consanguinity
- Birth history: Prematurity, NICU admission (delayed TSH elevation risk)
- Sibling history: Dyshormonogenesis is autosomal recessive — siblings may be affected
Pendred syndrome is an autosomal recessive disorder due to mutation in the SLC26A4 gene (Pendrin) encoding an anion transporter involved in iodide transport in the thyroid and endolymph in the inner ear.
- Triad: Sensorineural deafness + Goiter + Partial iodide organification defect
- Partial organification defect — TSH may be mildly elevated; goiter develops in childhood/adolescence
- Perchlorate discharge test: >10% discharge confirms organification defect
- Dilated vestibular aqueduct on CT temporal bone (Mondini dysplasia)
- Most common cause of syndromic sensorineural deafness with goiter
| Syndrome/Association | Gene/Mechanism | Features in Addition to CH |
|---|---|---|
| Down syndrome (Trisomy 21) | Chromosome 21 trisomy | ~28% have CH; all Down syndrome babies need TSH at birth, 2-4 wks, 6 months, 12 months |
| Bamforth-Lazarus syndrome | FOXE1 | Spiky hair, cleft palate, choanal atresia, bifid epiglottis |
| Brain-lung-thyroid syndrome | NKX2-1 (TTF-1) | CH + respiratory distress syndrome + benign hereditary chorea |
| Pendred syndrome | SLC26A4 | Sensorineural deafness + goiter (see above) |
| Hypothyroidism + Renal abnormalities | PAX8 | CH + renal hypoplasia |
🩺 Examination — Exam Q&A
Systematic examination approach:
- General: Hypoactive, lethargic; feels cold to touch; hypothermia; pallor
- Anthropometry: Low weight for age (failure to thrive); short length; increased head circumference (pseudohydrocephalus in severe untreated)
- Skin: Dry, rough, scaly, pale, mottled; myxedematous (non-pitting, doughy edema); carotenemia
- Hair: Coarse, scanty, brittle; posterior hairline low; thin outer third of eyebrows
- Face: Coarse facies, puffy periorbital edema, depressed nasal bridge, macroglossia, thick lips, protrusion of tongue
- Fontanelles: Wide anterior fontanelle + patent posterior fontanelle (normally closes by 6–8 weeks) — key sign
- Neck: Goiter if dyshormonogenesis; absent/small if dysgenesis; midline swelling at base of tongue (lingual thyroid — ask child to stick out tongue)
- Abdomen: Protuberant (pot-belly), umbilical hernia, constipation
- Cardiovascular: Bradycardia, low-volume pulse, muffled heart sounds (pericardial effusion)
- Neurological: Hypotonia, delayed DTR relaxation (hung-up reflexes), sluggish Moro reflex
The posterior fontanelle normally closes by 6–8 weeks of age. A posterior fontanelle >0.5 cm at birth, or any patent posterior fontanelle beyond 6–8 weeks, is an important early clinical sign of congenital hypothyroidism and should prompt thyroid function testing.
Only ~3% of normal neonates have a posterior fontanelle larger than 0.5 cm — making it a specific finding for CH when present.
Both fontanelles are large due to delayed bone maturation (retarded ossification) caused by thyroid hormone deficiency.
Hung-up reflexes (also called delayed relaxation of deep tendon reflexes) refer to prolonged return of the limb to its original position after the reflex response is elicited. Best demonstrated at the ankle (Achilles reflex).
- Mechanism: Thyroid hormone is required for normal relaxation of myosin-actin crossbridges; its deficiency slows the relaxation phase of muscle contraction
- Significance: Pathognomonic of hypothyroidism — both congenital and acquired. The Achilles reflex is the most sensitive DTR for hypothyroidism
- In infants, may be assessed by watching the return of the foot after eliciting ankle jerk
Myxedema is the accumulation of mucopolysaccharides (glycosaminoglycans — hyaluronic acid, chondroitin sulfate) in the dermis and subcutaneous tissues due to thyroid hormone deficiency.
| Feature | Myxedema | Pitting Edema |
|---|---|---|
| Pitting | Non-pitting (firm, doughy) | Pitting |
| Cause | Mucopolysaccharide deposition | Fluid accumulation (hypoproteinemia, heart failure, etc.) |
| Location | Diffuse — face, tongue, hands, periorbital | Dependent areas — legs, ankles |
| Skin | Dry, waxy, yellowish | Normal or shiny skin |
Goiter examination:
- Inspect — swelling in lower anterior neck; moves up with swallowing
- Palpate from behind — bilobar enlargement, consistency (soft/firm/hard), tenderness, bruit (hypervascular gland)
- Percuss — retrosternal extension (dullness over manubrium)
- Auscultate — thyroid bruit (Graves' disease)
Goiter in CH signifies:
- Dyshormonogenesis: Enzyme defect in T4 synthesis → high TSH → TSH-driven compensatory thyroid hyperplasia → goiter (always present)
- Iodine deficiency: Compensatory hyperplasia
- Maternal antithyroid drugs or antibodies — may cause transient goitrous CH
- Absent goiter → suggests thyroid dysgenesis (agenesis, ectopia) or TSH deficiency (central CH)
💡 Exam Pearl
Goiter = dyshormonogenesis; No goiter = dysgenesis. This distinction guides imaging and genetic workup.
- Decline in school performance and cognitive slowdown
- Fatigue, lethargy, cold intolerance
- Weight gain despite poor appetite, constipation
- Growth failure — short stature without proportionate weight loss (characteristic — obese short child)
- Delayed puberty (usually) OR precocious puberty in very severe, longstanding hypothyroidism (Van Wyk-Grumbach syndrome)
- Goiter (Hashimoto's thyroiditis most common cause in childhood)
- Myxedematous features (dry skin, hair, hung-up reflexes)
- Galactorrhea (TRH stimulates prolactin in severe hypothyroidism)
- Bradycardia, prolonged QTc, pericardial effusion
Van Wyk-Grumbach syndrome is precocious puberty in the setting of severe, longstanding primary hypothyroidism — a paradox since most hypothyroid children have delayed puberty.
- Mechanism: Massively elevated TSH cross-reacts with FSH receptor (structural similarity); also elevated TRH stimulates prolactin. Result: premature breast development (girls), testicular enlargement (boys), galactorrhea
- Key features: Breast development + galactorrhea in girls; macroorchidism (enlarged testes) in boys, WITHOUT adrenarche (no pubic or axillary hair) — because adrenal androgen axis is not activated
- Treatment: Levothyroxine replacement — pubertal changes regress with treatment
- Bone age: Severely delayed (unlike central precocious puberty where it is advanced)
| Feature | Congenital Hypothyroidism | Down Syndrome |
|---|---|---|
| Facies | Coarse, puffy, myxedematous | Flat facies, upslanting palpebral fissures, epicanthal folds |
| Tongue | Macroglossia (large tongue) | Protruding tongue (normal-sized but in small oral cavity) |
| Eyes | Periorbital puffiness | Upslanting palpebral fissures, Brushfield spots, epicanthal folds |
| Hands | Puffy, myxedematous | Simian crease, short clinodactyly of 5th digit |
| Hypotonia | Present | Present (more profound) |
| Reflexes | Hung-up (delayed relaxation) | Normal or reduced (not hung-up) |
| Fontanelle | Large (both anterior and posterior) | Large anterior fontanelle |
| Thyroid function | Abnormal (↑TSH, ↓T4) | Often normal; but ~28% have associated CH |
| Chromosomes | Normal | Trisomy 21 |
🚨 Important
Down syndrome and CH can coexist — always check thyroid function in Down syndrome babies.
🔬 Investigations — Exam Q&A
Newborn screening (NBS) is the cornerstone of CH diagnosis, enabling treatment before clinical manifestations appear.
Sample: Heel-prick capillary blood on filter paper (Guthrie card).
Timing:
- Term infants: 48–72 hours after birth (to avoid falsely elevated TSH in the first 24–48 hours due to the physiological TSH surge at birth)
- Premature and low birth weight infants: Repeat at 2 weeks and 4 weeks (risk of delayed TSH elevation)
- Cord blood: Can be used (TSH cut-off ≥20 mIU/L); used in some Indian programs
Three strategies:
| Strategy | Method | Advantage |
|---|---|---|
| Primary TSH (most common worldwide) | TSH alone; T4 if TSH elevated | Cost-effective; detects primary CH |
| Primary T4 + reflexive TSH | T4 first; TSH if T4 low | Detects central (secondary) CH |
| Simultaneous TSH + T4 | Both measured | Most comprehensive; expensive |
Cut-off for primary TSH strategy (India): TSH ≥20 mIU/L on cord blood or ≥10–15 mIU/L on postnatal heel-prick → recall for confirmatory testing.
🚨 Limitation
Primary TSH strategy misses central (secondary/tertiary) CH because TSH is low or normal. Central CH requires T4 measurement for detection.
After a positive NBS, serum confirmatory tests must be done as soon as possible:
- Serum TSH: Elevated in primary CH (most sensitive and specific test for primary CH)
- Serum free T4 (FT4): Decreased in primary CH; gives severity
- Total T4: Less reliable than FT4 (affected by TBG levels)
Diagnostic criteria for primary CH on confirmatory testing:
- TSH > 10 mIU/L (in neonates >48 hours) + low FT4 → confirmed primary CH
- TSH > 10–40 mIU/L + FT4 normal → mild/subclinical CH or transient hyperthyrotropinemia
💡 Goal
Treatment should begin by 14 days of life — earlier the better for neurodevelopmental outcome.
| Investigation | What It Shows | Key Points |
|---|---|---|
| Thyroid Scintigraphy (99mTc or 123I) | Functional thyroid tissue; ectopic thyroid location; agenesis (no uptake) | Gold standard for etiology; must be done BEFORE L-T4 (or may delay briefly); 123I preferred over 99mTc as it also gives iodine organification info |
| Thyroid Ultrasonography | Anatomical size and location; ectopic gland; goiter | Cannot assess function; may miss ectopic (non-neck) thyroid; combined use with scintigraphy most informative |
| Perchlorate Discharge Test | Iodine organification defect; >10% discharge = abnormal | Done with 123I; confirms dyshormonogenesis; diagnoses Pendred syndrome |
✅ Key Guideline Point (ENDO-ERN 2021, AAP 2023)
Do NOT delay treatment for imaging. Start L-T4 first; imaging can be done simultaneously or shortly after to determine etiology and permanence. Treatment takes priority over investigations.
X-ray of the knee (distal femoral and proximal tibial epiphyses) is used to assess the severity of intrauterine hypothyroidism and bone maturation:
- At full term, the distal femoral and proximal tibial epiphyses are normally ossified
- In CH: Absent or delayed epiphyseal ossification = severe intrauterine thyroid hormone deficiency
- Also shows epiphyseal dysgenesis (irregular, fragmented ossification centers) — characteristic of severe hypothyroidism
- Correlates with neurodevelopmental outcome: absent epiphyses → more severe brain injury prenatally
- Bone age is retarded throughout skeleton
- Thyroglobulin (TG): Undetectable in athyreosis; elevated in dyshormonogenesis and ectopic thyroid. Helps distinguish agenesis (no TG) from ectopia (some TG)
- Anti-TPO and anti-Tg antibodies: In mother — to detect autoimmune cause of transient CH. Maternal TRAb (blocking antibodies) tested if suspected transient CH
- Serum calcium: Rarely needed; hypocalcemia if associated hypoparathyroidism (DiGeorge)
- CBC: Macrocytic or normocytic anemia in hypothyroidism (decreased erythropoietin response)
- Serum cholesterol and triglycerides: Elevated in hypothyroidism (decreased LDL receptor activity) — less relevant in neonates
- CK (creatine kinase): Elevated in hypothyroid myopathy
- Urine iodine: To assess iodine status; rules out iodine deficiency as cause
- Genetic testing: If family history, consanguinity, or syndromic features — targeted gene panel (TSHR, PAX8, NKX2-1, TPO, DUOX2, TG, SLC5A5, SLC26A4)
Chest X-ray:
- Cardiomegaly (globular shape if pericardial effusion present)
- Pleural effusion (myxedema)
ECG:
- Sinus bradycardia
- Low voltage complexes (limb leads and precordial) — due to pericardial effusion and myxedematous infiltration
- Prolonged QTc interval — risk of arrhythmia in severe hypothyroidism
- Flat or inverted T waves
Echocardiography: Pericardial effusion; may show dilated cardiomyopathy in severe longstanding CH. Also important as ~14% of CH patients have congenital heart defects (septal defects commonest).
| TSH | Free T4 | Diagnosis |
|---|---|---|
| ↑↑ (high) | ↓ (low) | Primary hypothyroidism (CH — overt) |
| ↑ (mildly elevated) | Normal | Subclinical hypothyroidism / compensated CH / transient hyperthyrotropinemia |
| Normal or ↓ | ↓ | Central (secondary or tertiary) hypothyroidism |
| Normal | Normal | Euthyroid |
| ↑↑ | ↑ or normal | Thyroid hormone resistance (rare) |
| Normal | ↓ (total T4 low) | TBG deficiency (benign X-linked; free T4 will be normal) |
💡 Neonatal TSH normal values
TSH surges at birth (up to 60–80 mIU/L in first few hours) then normalizes within 24–48 hrs. NBS TSH at 48–72 hours: normal < 6–10 mIU/L depending on laboratory. This physiological surge must not be confused with CH.
💊 Management — Exam Q&A
Treatment: Oral Levothyroxine (L-T4, synthetic T4)
- Dose: 10–15 mcg/kg/day (higher dose for severe/overt CH)
- Formulation: Tablet (crushed and dissolved in small amount of breast milk or water); liquid preparation available
- Start by: 14 days of life — ideally within 7–10 days; the earlier the better
- Why not T3 (triiodothyronine)? T4 is preferred because the brain converts T4 to T3 locally, providing sustained and regulated supply. T3 would cause fluctuating levels.
- Why not combined T3+T4? Not recommended routinely; T4 alone is standard of care
✅ Drug Administration Instructions
L-T4 tablets should be given crushed, 30 minutes before feeds. Avoid concurrent administration with soy formula, iron, calcium, and antacids — they reduce absorption. Cow's milk also reduces absorption.
Treatment targets (AAP 2023, ENDO-ERN 2021):
- Free T4: Maintain in the upper half of the age-specific reference range during the first 3 years of life (critical period of brain development)
- TSH: Normalize to 0.5–2.0 mIU/L
- Goal: FT4 should normalize within 2 weeks, TSH within 4 weeks of starting treatment
Monitoring schedule:
| Age | Monitoring Frequency |
|---|---|
| First 6 months | Every 1–2 months |
| 6–12 months | Every 2–3 months |
| 1–3 years | Every 3–4 months |
| >3 years | Every 6–12 months |
Neurodevelopmental assessment, hearing, and growth monitoring at every visit.
Determination is done by a trial off levothyroxine at age 3 years (when critical brain development is complete):
- Reduce dose and stop L-T4 for 30 days
- Measure TSH and FT4 at 30 days off treatment
- If TSH rises > 10 mIU/L and FT4 drops → permanent CH → lifelong L-T4
- If TSH and FT4 remain normal → transient CH → treatment can be discontinued
Clues suggesting permanent CH: Thyroid agenesis/severe ectopia on imaging, very high initial TSH, very low initial T4, known genetic mutation
Clues suggesting transient CH: Maternal blocking antibodies, maternal ATD use, iodine excess, normal or near-normal imaging, mild TSH elevation on NBS
- Treated before 2 weeks: Normal or near-normal IQ; grossly normal neurodevelopmental outcome
- Treated between 2–4 weeks: Slightly reduced IQ (~5–10 points); mostly normal outcome
- Untreated/delayed treatment: Severe intellectual disability (IQ < 70), spasticity, deafness — irreversible
- Even with early treatment, subtle deficits in verbal skills, attention, memory, and fine motor function may persist — especially in severe CH (athyreosis)
- ~10% of CH children have hearing impairment — audiological evaluation is mandatory
- Children with thyroid agenesis tend to have slightly lower IQ than those with ectopia — due to more severe prenatal thyroid hormone deficiency
💡 Most Important Prognostic Factor
Age at initiation of treatment + adequacy of early L-T4 dose are the two most critical determinants of intellectual outcome.
- Craniosynostosis — premature fusion of cranial sutures; most serious complication of over-treatment in neonates
- Irritability, poor sleep, excessive sweating
- Accelerated bone age → premature closure of growth plates → short final height
- Tachycardia, arrhythmias
- Behavioral problems, hyperactivity
- Thyrotoxicosis features if severe over-treatment
This is why regular monitoring is essential — underdosing risks intellectual disability; overdosing risks craniosynostosis and advanced bone age.
Subclinical hypothyroidism (SH) = elevated TSH with normal FT4, no symptoms.
- If TSH 5–10 mIU/L: Observe and repeat TFT in 4–6 weeks; most are transient, especially in neonates
- If TSH 10–40 mIU/L in infants < 3 years: Treat with L-T4 (critical period of brain development)
- If TSH > 40 mIU/L: Always treat regardless of age
- If TSH 5–10 mIU/L in older children: Treat if symptomatic, or if TSH persistently elevated on repeat, or if anti-TPO positive (Hashimoto's — risk of progression to overt hypothyroidism)
- Down syndrome: Lower threshold to treat; TSH > 6 mIU/L → treat
- Universal salt iodization (USI) is the most effective public health intervention to prevent iodine deficiency-related CH
- India's National Iodine Deficiency Disorders Control Programme (NIDDCP) mandates iodized salt (≥15 ppm iodine at production)
- Pregnant and lactating women require 220–290 mcg/day iodine (WHO recommendation)
- Iodine supplementation during pregnancy in deficient areas prevents endemic cretinism and reduces incidence of transient CH
- Breastfed infants: Mother's iodine intake critical; formula-fed infants: iodine added to formula
- Excessive iodine also harmful (Wolff-Chaikoff effect causing transient hypothyroidism) — use of povidone iodine in delivery/NICU should be minimized or replaced with chlorhexidine
🔭 Recent Advances — Exam Q&A
- Lowering of TSH cut-offs has led to identification of a larger group of mild/subclinical CH — creating controversy about whether all these need treatment
- Second screening is now recommended (AAP 2023, ENDO-ERN 2021) for: preterm (<37 weeks), LBW (<2.5 kg), twin pregnancies (dilution effect), NICU admissions — to detect delayed TSH elevation
- Simultaneous T4+TSH strategy is gaining favor for comprehensive detection including central CH
- In India: Expansion of NBS programs under RBSK (Rashtriya Bal Swasthya Karyakram) to include CH at state level
- Point-of-care TSH testing for NBS in resource-limited settings is being studied
- Liquid L-T4 formulations: Better dose accuracy for neonates/infants compared to crushed tablets; may improve compliance; available in some countries
- Higher initial dose (15–17 mcg/kg/day) in severe CH (athyreosis, extremely low T4) has shown better early neurodevelopmental outcomes — studied in recent trials (ENDO-ERN 2021 recommends 10–15 mcg/kg/day)
- Once-weekly L-T4 dosing has been studied in stable older patients for compliance — not recommended in infants
- Soft gel capsule formulations — better bioavailability and less susceptibility to food/drug interactions compared to traditional tablets — now available in some countries
- Genetic testing is increasingly used to confirm etiology and counsel families, especially in:
- Dyshormonogenesis (autosomal recessive — risk to siblings is 25%)
- Familial dysgenesis (rare, but genes like PAX8, NKX2-1 identified)
- Syndromic CH (NKX2-1 for brain-lung-thyroid; FOXE1 for Bamforth-Lazarus)
- Central CH — PIT1, PROP1, LHX3/4, HESX1 mutations
- Next-generation sequencing (NGS) panels can simultaneously test multiple CH-related genes
- Genetic diagnosis allows prediction of permanence and recurrence risk — avoids unnecessary re-testing at age 3 years for known permanent causes
- In India, genetic testing for CH is becoming more accessible through programs like ICMR-NNF India collaborative
- ~28% of Down syndrome (Trisomy 21) children have CH or thyroid dysfunction
- Screening protocol in Down syndrome (AAP 2023 update):
- NBS at birth (standard)
- Repeat serum TSH at 2–4 weeks of age (to detect delayed TSH rise)
- Serum TSH at 6 months and 12 months of age
- Then annually throughout life
- Higher risk of both congenital and acquired hypothyroidism; also higher risk of hyperthyroidism (Graves' disease)
- Lower threshold for treatment: TSH > 6 mIU/L in Down syndrome → treat
- Transient CH from maternal TSH receptor-blocking antibodies more common in Down syndrome
- Despite early treatment, studies show children with CH have mild but consistent deficits in working memory, processing speed, attention, and executive function compared to unaffected siblings (even with early treatment)
- The degree of prenatal hypothyroidism (reflected in bone age and initial T4 level at diagnosis) is the major predictor of these subtle deficits
- Hearing impairment in ~10% of CH children — universal hearing screen recommended; may be due to cochlear hypothyroidism or associated syndromic CH (Pendred)
- Neurodevelopmental surveillance and early intervention (speech therapy, occupational therapy) are part of standard CH follow-up
- Long-term follow-up into adulthood is recommended — transition from pediatric to adult endocrinology care is an important clinical milestone
⚡ Key Points — Quick Revision
One-Liners for Exam
- Most common preventable cause of intellectual disability: Congenital Hypothyroidism
- Most common pediatric endocrine disorder: Congenital Hypothyroidism
- Incidence: 1 in 2,000–4,000 worldwide; ~1 in 1,031 in non-endemic India
- Gender: F:M = 2:1
- Most common cause globally: Thyroid dysgenesis (80–85%); most common type = Agenesis (athyreosis)
- In India: Dyshormonogenesis proportionally higher (~39%); agenesis commonest within dysgenesis
- Goiter present: Dyshormonogenesis (autosomal recessive)
- Goiter absent: Thyroid dysgenesis
- Most common ectopic thyroid location: Lingual thyroid (base of tongue)
- Most common dyshormonogenesis gene mutation: TPO (iodine organification defect)
- Why asymptomatic at birth? Maternal T4 transfer (25–50%) partially protects the neonate
- Key early sign: Prolonged jaundice >3 weeks in a term baby — must check TFT
- Large posterior fontanelle >0.5 cm at birth: Must check TFT — only 3% of normal neonates have this
- Pathognomonic sign: Hung-up reflexes (delayed relaxation of DTR)
- Myxedema: Non-pitting edema due to mucopolysaccharide deposition — not fluid
- NBS timing: 48–72 hours (term); repeat at 2 and 4 weeks in preterm/LBW
- Confirmatory test: Serum TSH + Free T4
- Gold standard for etiology: Thyroid scintigraphy (99mTc or 123I)
- Treatment: L-T4, 10–15 mcg/kg/day; start by 14 days of life
- Treatment target: FT4 in upper half of normal; TSH 0.5–2.0 mIU/L
- Permanence check: Trial off L-T4 at age 3 years
- Over-treatment risk: Craniosynostosis
- Pendred syndrome: Goitrous CH + sensorineural deafness; SLC26A4 mutation
- Van Wyk-Grumbach syndrome: Precocious puberty (breast/testicular enlargement) in severe longstanding hypothyroidism; no adrenarche; regresses with L-T4
- Down syndrome screening: NBS + repeat at 2–4 weeks + TSH at 6 and 12 months + then annually
- Knee X-ray: Assesses severity of intrauterine hypothyroidism; absent epiphyseal ossification = severe prenatal deficiency
- Brain-lung-thyroid syndrome: NKX2-1 gene; CH + RDS + benign hereditary chorea
⚡ Drug Interaction Alert
Levothyroxine absorption is reduced by: Iron supplements, Calcium, Soy formula, Cow's milk, Antacids, Proton pump inhibitors, Cholestyramine. Give L-T4 30 minutes before feeds, at least 4 hours apart from these substances.
🚨 Exam Traps
- CH is more common in females (2:1) — unlike most autosomal conditions
- Soft murmur of pericardial effusion vs. hard VSD murmur — both can coexist (14% of CH have congenital heart defects)
- Primary TSH-only NBS misses central (secondary) CH — always note this limitation
- In dyshormonogenesis, the goiter may not be present at birth — it develops later due to persistent TSH stimulation; do not rule out dyshormonogenesis in newborn based on absence of goiter at birth
- Do NOT delay L-T4 treatment for imaging — treat first, investigate to find etiology afterward