Paediatrics: Acquired hypothyroidism

Acquired hypothyroidism

A relatively common condition with an estimated prevalence of 0.1–0.2% in the population. The incidence in girls is 5–10 times greater than in boys.

Aetiology

Acquired hypothyroidism may be due to a primary thyroid problem or indirectly to a central disorder of hypothalamic-pituitary function.

Primary hypothyroidism (raised TSH; low T4/T3)

• Autoimmune (Hashimoto’s or chronic lymphocytic thyroiditis).
• Iodine deficiency: most common cause worldwide.
• Subacute thyroiditis.
• Drugs (e.g. amiodarone, lithium).
• Post-irradiation thyroid (e.g. bone marrow transplant—total body irradiation).
• Post-ablative (radioiodine therapy or surgery).

Central hypothyroidism (low serum TSH and low T4) 

Hypothyroidism due to either pituitary or hypothalamic dysfunction.

• Intracranial tumours/masses.
• Post-cranial radiotherapy/surgery.
• Developmental pituitary defects (genetic, e.g. PROP-1, Pit-1genes): isolated TSH deficiency; multiple pituitary hormone deficiencies.

Clinical features

The symptoms and signs of acquired hypothyroidism are usually insidious and can be extremely difficult to diagnose clinically. A high index of suspicion is needed.

• Goitre: primary hypothyroidism.
• Increased weight gain/obesity.
• Decreased growth velocity/delayed puberty.
• Delayed skeletal maturation (bone age).
• Fatigue: mental slowness; deteriorating school performance.
• Constipation: cold intolerance; bradycardia.
• Dry skin: coarse hair.
• Pseudo-puberty: girls—isolated breast development; boys—isolated testicular enlargement.
• Slipped upper (capital) femoral epiphysis: hip pain/limp.

Diagnosis

Diagnosis is dependent on biochemical confirmation of hypothyroid state.

• Thyroid function tests: high TSH/low T4/low T3.
• Thyroid antibody screen. Raised antibody titres:
• antithyroid peroxidase;
• anti-thyroglobulin;
• TSH receptor (blocking type).

Treatment

• Oral Levothyroxine (25–200 micrograms/day).
• Monitor thyroid function test every 4–6mths during childhood.

 Monitor growth and neurodevelopment.