CONGENITAL HYPOTHYROIDISM
DEFINITION:
A congenital disorder of thyroid metabolism characterized by a
lower than normal end organ effect of thyroid hormone resulting in
the signs and symptoms of hypothyroidism.
EPIDEMIOLOGY:
- incidence: 1/4,000
- age of onset:
- risk factors:
PATHOGENESIS:
- developmental defects of the thyroid gland (dysgenesis,
hypoplastic, agenesis, ectopia) account for 90% of the cases of
congenital hypothyroidism and may be familial or sporadic
- most newborns are asymptomatic due to the transplacental
passage of moderate amounts of maternal T4 (can produce levels
in the fetus 25-50% of normal)
- other causes of congenital hypothyroidism include TSH-Binding
Inhibitory Antibody (TBIAb), maternal radioiodine or iodine
exposure, TRH or TSH Deficiencies, TSH or Thyroid Hormone
Unresponsiveness, Inborn Errors of Thyroid Metabolism
CLINICAL FEATURES:
- infantile hypotonia
- lack of crying ("good baby")
- psychomotor delay
- sluggish/disinterested
- somnolence
2. Respiratory Manifestations
- apnea
- choking spells with feeds
- nasal obstruction
- noisy respirations
- respiratory distress syndrome
3. Cardiovascular Manifestations
- cardiomegaly
- murmers
- slow heart rate
4. Gastrointestinal Manifestations
- constipation
- delayed dentation
- feeding difficulties
- high birth weight
- large abdomen
- macroglossia
- poor appetite
- prolonged jaundice
- unbilical hernia
5. Cutaneous Manifestations
- carotenemia
- coarse, brittle, scanty hair
- cold and mottled skin
- deep, hoarse voice
- dry, scaly skin
- edema of genitals & extremities
- low hairline
- myxedema
6. Musculoskeletal Manifestations
- normal body weight but decreased length
- normal or increased head size
- broad, short fingers
- pseudohypertrophy (calf)
- short limbs
- short thick neck
7. Endocrine Manifestations
- goiter (with error of thyroid metabolism)
INVESTIGATIONS:
- all neonates are screen at 48 hours for TSH (and/or T4) from
a blood drop placed on filter paper (avoids the TSH surge at
birth due to stress producing false positive results)
- screens for primary hypothyroidism
- if result is <0.20 mIU/L
- see patient immediately for history/physical, to draw a
stat serum T4 and TSH, and to start thyroid hormone therapy
(see below)
2. Serum
- elevated TSH and reduced T4
- anemia
- unconjugated hyperbilirubinemia
3. Imaging Studies
- radioactive technetium to detect developmental defects of
the thyroid (i.e., dysgenesis, ectopia, etc.)
2. Skeletal X-Rays
- for baseline bone age
- retardation of osseous development
- absence of distal femoral epiphysis
- epiphyses with multiple foci or ossification (epiphyseal
dysgenesis)
- deformity ("beaking") of the 12th thoracic or 1st or 2nd
lumbar vertebrae
3. Skull X-Rays
- large anterior and posterior fontanelle
- side sutures
- wormian bones
- enlarged sella turcia +/- erosion and thinning
4. 2D Echo
- cardiomegaly +/- pericardial effusion
4. ECG
- low voltage P, QRS, T waves
MANAGEMENT:
- begin with positive screen as the test results are
returned in 10 days and thus the infant has been untreated for
this period
- start thyroid hormone at 6 ug/kg po od
- arrange for bone age and radionuclide scan
2. Maintenance
- see initially at 3 and 6 months of age then q6m
- moniter TSH, T4 levels, growth parameters, clinically
- moniter bone age q1y to ensure adequate osseous
development (will be delayed with undertreatment)
- full developmental assessment (with hearing tests) at 8-9
months of age and at school entry
- long term follow-up is required as this is a chronic
life-long disorder
2. Prognosis
- normal growth, intelligence, and life span if detected
within the first few weeks of life
- short stature, mental retardation, and delayed puberty with
delays in detection, progressive ataxia
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