Hypothyroidism Flashcards
Congenital hypothyroidism - background
- Hypothyroidism from birth resulting from insufficient secretion of thyroid hormones
- Relatively common condition - 1/4000 births. Twice as common in girls than in boys
- One the few preventable causes of severe learning difficulties
Congenital hypothyroidism - causes (4)
- Thyroid dysgenesis (85%) = maldescent of thyroid and athyrosis. Results in thyroid aplasia/hypoplasia, ectopic thyroid (lingual/sublingual)
- Thyroid hormone biosynthetic defect (15%) = hereditary, e.g. Pendred’s syndrome
- Iodine deficiency (rare in developed countries but common worldwide)
- Congenital TSH deficiency = rare, associated with other pituitary hormone deficiencies
Congenital hypothyroidism - clinical features
- Usually asymptomatic and picked up on screening
- FTT, feeding problems, constipation
- Prolonged jaundice
- Pale, cold, mottled dry skin
- Coarse facies, large tongue, goitre (occasionally), umbilical hernia
Congenital hypothyroidism - dx
National neonatal biochemical screening programs:
- Test in first week of life
- Blood spot - filter paper collection (Guthrie card)
- TSH (high) and/or free T4 (low) estimation
Thyroid imaging also recommended to determine if cause is due to thyroid dysgenesis or hormone biosynthetic disorder
- Thyroid US
- Radionucleotide scanning (99T or 131I)
Congenital hypothyroidism - complications (if not treated)
Without tx, can have:
- Neurodevelopmental delay and mental retardation
- Poor motor coordination
- Hypotonia
- Ataxia
- Poor growth and short stature
Congenital hypothyroidism - mx
- Start replacement therapy as soon as dx made (within 1-2d) to prevent intellectual disability
- Thyroxine 10-12mcg/kg orally, daily, titrating according to TSH and free T4 response
- Given as crushed tablets
Monitoring/follow-up
- Monitor intellectual and physical development along with TFTs = every 2-3mo in the first five years, then every 3-6mo
- Mx with consultation with a paediatric endocrinologist. Tx generally lifelong but in some cases may be transient
Acquired hypothyroidism - overview
- Relatively common condition, estimated prevalence 0.1-0.2%
- Incidence in girls 5-10x greater than boys
- Etiology = may be due to primary thyroid problem or indirectly to a central disorder of hypothalamic-pituitary disorder
Acquired hypothyroidism - causes
Primary hypothyroidism (raised TSH, low T4/T3) (5)
- Autoimmune (Hashimoto’s or chronic lymphocytic thyroidism) = common
- Iodine deficiency = most common cause worldwide
- Subacute thyroiditis
- Drugs (e.g. amiodarone, lithium)
- Post-irradiation thyroid (e.g. bone marrow transplant - total body irradiation), or post-ablative (radioiodine therapy or surgery)
Central hypothyroidism (low serum TSH and low T4) = hypothyroidism due to either pituitary or hypothalamic dysfunction (3)
- Intracranial tumours/masses
- Post-cranial radiotherapy/surgery
- Developmental pituitary defects (e.g. genetic, such as PROP-1 and Pit-1 genes)
Acquired hypothyroidism - RF/association
- DS
- Turner’s syndrome
- Vitiligo
- Rheumatoid arthritis
- DM
(+ Addison’s disease)
Acquired hypothyroidism - clinical features
- Goitre = primary hypothyroidism
- Increased weight gain/obesity, decreased growth velocity, delayed puberty
- Fatigue, mental slowness, deteriorating school performance
- Constipation
- Other = dry skin/coarse hair, slipped upper femoral epiphysis (hip pain/limp), bradycardia
Acquired hypothyroidism - dx/ix
Dependent on biochemical confirmation of hypothyroid state.
A. Thyroid function tests
1. High TSH
2. Low T4 or low T3
B. Thyroid antibody screen (looking for raised antibody titres):
- Antithyroid peroxidase
- Anti-thyroglobulin
- TSH receptor (blocking type)
Acquired hypothyroidism - tx (3)
- Thyroxine 85-105mcg/m2 orally, daily, with titration according to TSH and free T4 response
- Monitor TFTs every 4-6 mo during childhood
- Monitor growth and neurodevelopment
