Congenital hypothyroidism
Incidence
In the US: The incidence of congenital hypothyroidism, as detected through newborn screening, is approximately 1 per 4000. Internationally: In areas of iodine deficiency, the prevalence of goiter is reported to range from 5-15% of the population. Some of the highest incidences (1 in 1400 to 1 in 2000) have been reported from various locations in the Middle East.
Clinical Characteristics
Congenital hypothyroidism is a disorder of the thyroid metabolism characterized by a lower than normal effect of thyroid hormone. The incidence in the population is 1:4,000. A developmental defects of the thyroid gland (dysgenesis, hypoplastic, agenesis, ectopia) account for 90% of the cases of congenital hypothyroidism. While percentages of specific etiologies vary from country to country, ranges are as follows: Ectopic thyroid, 25-50% . Thyroid agenesis, 20-50% . Dyshormonogenesis, 4-15% . Hypothalamic-pituitary dysfunction, 10-15%. It may be familial or sporadic. In the absence of treatment it leads to infantile hypotonia, lack of crying, psychomotor delay, somnolence, respiratory distress syndrome, cardiomegaly, slow heart rate, constipation, delayed dentation, macroglossia and goiter. Infants with obvious findings of hypothyroidism (eg, macroglossia, enlarged fontanelle, hypotonia) at the time of diagnosis have IQs 10-20 points lower than infants without such findings. Anemia is due to decreased oxygen carrying requirement. Hyperreflexive jerk with profound slowing of the return phase occurs. All neonates are now screened at 48 hours for TSH (and/or T4) from a blood drop placed on filter paper. If screened positive the infant is given thyroid hormone.The prognosis is good: normal growth, intelligence, and life span if detected within the first few weeks of life.
Precipitants
None.
Provocation Tests
None.
Diagnostic Procedures
Diagnosis of primary hypothyroidism is confirmed by demonstrating decreased levels of serum thyroid hormone (total or free T4) and elevated levels of TSH. If maternal antibody-mediated hypothyroidism is suspected, maternal or neonatal antithyroid antibodies may confirm the diagnosis.