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 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-1 genes): 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 sus-picion 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.