[36] Congenital Hypothyroidism Flashcards
What is congenital hypothyroidism?
A condition of thyroid hormone deficiency present at birth
Why is congenital hypothyroidism important to detect in neonatal screening?
- Relatively common
- Preventable cause of severe learning difficulties
What is the most common cause of sporadic congenital hypothyroidism?
Maldescent of the thyroid and athyrosis
What normally happens to the thyroid during early fetal life?
The thyroid migrates from a position at the base of the tongue to its normal site below the larynx
What happens to the thyroid in maldescent?
The thyroid remains as a lingual mass or a unilobular small gland
What is the reason for the failure of formation or migration of the thyroid?
Not well understood
Other than maldescent of the thyroid and athyrosis, what are the causes of congential hypothyroidism?
- Dyshormonogenesis
- Iodine deficiency
- Hypothyroidism due to TSH deficiency
What is dyshormonogenesis?
An inborn error of thyroid hormone synthesis
What is hypothyroidism due to TSH deficiency usually associated with?
Pituitary dysfunction
What is the significance of hypothyroidism due to TSH deficiency being associated with pituitary dysfunction?
The pituitary dysfunction usually manifests in other ways before hypothyroidism is evident
What are the risk factors for dyshormonogenesis?
More common in ethnic groups with consanguineous marriage
What is the problem with the early diagnosis of congenital hypothyroidism?
They are difficult to differentiate from normal in the first month of life
What happens to the clinical features of congential hypothyroidism with age?
They become more prominent
What are the clinical features of congential hypothyroidism?
- Feeding problems
- Constipation
- Faltering growth
- Prolonged jaundice
- Pale, cold, mottled dry skin
- Coarse facies
- Large tongue
- Hoarse cry
- Goitre
- Umbilical hernia
- Delayed development
How are most infants with congenital hypothyroidism picked up?
Routine neonatal biochemical screening
How does congential hypothyroidism present on routine neonatal biochemical screening?
Raised TSH in the blood, done by a blood spot on filter paper, called the ‘Guthrie card’
What is recommended in infants who are identified to have congential hypothyroidism?
Thyroid imaging
What is the purpose of thyroid imaging in congenital hypothyroidism?
Determine if the cause is due to thyroid dysgenesis, or due to hormone biosynthetic disorders
What thyroid imaging may be used in congential hypothyroidism?
- Ultrasound
- Radionucleotide scanning
What is the treatment for congential hypothyroidism?
Thyroxine
When should treatment with thyroxine be started in congenital hypothyroidism?
Before 2-3 weeks of age
Why is it important that treatment with thyroxine is started before 2-3 weeks of age in congenital hypothyroidism?
To reduce the risk of impaired neurodevelopment
How long is treatment required for in congenital hypothyroidism?
Life-long
How is the dose of thyroxine determined in congenital hypothyroidism?
Titration of the dose to maintain normal growth, TSH, and T4 levels
How is therapy monitored in congenital hypothyroidism?
Measuring serum TSH and T3 levels
How often is therapy monitored in congenital hypothyroidism?
- Every 1-3 months in 1st year
- Every 2-3 months when 1-2 years of age
- Every 4-6 months when >2 years of age
What is the aim of treatment with thyroxine in congenital hypothyroidism?
To maintain T4 in upper 1/4 of normal range, and TSH in lower end of normal range.
What are the complications of congenital hypothyroidism?
Without early hormone replacemenmt therapy, a number of adverse sequelae may occur, including;
- Neurodevelopmental delay and mental retardation
- Poor motor coordination
- Hypotonia
- Ataxia
- Poor growth and short stature
