Juvenile hypothyroidism and hyperthyroidism

Overview

Thyroid disease that appears after the first year of life is taken to be acquired. Two conditions dominate:

• Juvenile (acquired) hypothyroidism, mostly from Hashimoto thyroiditis. It presents with growth failure, often without other obvious symptoms.
• Hyperthyroidism, which in children is nearly always Graves disease.

Both are autoimmune, both are commoner in girls, and both cluster with other autoimmune disorders such as type 1 diabetes.

Thyroid function tests: the basics

• FT4 (unbound T4) is the test of choice because it is not affected by binding-protein changes.
• TSH above normal usually means primary hypothyroidism; TSH below normal usually means hyperthyroidism.
• Use age-adjusted reference ranges.
• In early thyroid failure, TSH rises before FT4 falls.

Juvenile (acquired) hypothyroidism

Aetiology

Hashimoto thyroiditis

• Autoimmune attack with lymphocytic infiltration, lymphoid follicles, then fibrosis and atrophy.
• Usually starts after 6 years, peaks in adolescence; strong female predominance (Akbar quotes about 4:1).
• Family history of thyroid disease in about a quarter to a third.
• Goitre: diffuse, firm, non-tender, mobile, sometimes with a pebbly surface.
• The child may be euthyroid, hypothyroid, or briefly hyperthyroid ("hashitoxicosis").
• Commonest cause of goitre in children and adolescents.
• Down syndrome and Turner syndrome predispose.

Clinical features

• Slowing of growth (height velocity under about 5 cm per year), without weight loss; often weight gain. The child crosses height centiles downwards.
• Delayed bone age; immature (high) upper-to-lower segment ratio.
• Cold intolerance, tiredness, more sleep, constipation.
• Dry skin, pallor, puffy face.
• Slow-relaxing reflexes.
• Delayed puberty usually; but severe long-standing disease can cause precocious puberty or galactorrhoea.
• Some present with headache, visual problems or galactorrhoea.

Investigations

• TSH raised, FT4 (or total T4) low.
• Antithyroid peroxidase (anti-TPO) and antithyroglobulin antibodies confirm autoimmune disease.
• Delayed bone age on hand X-ray.
• Biopsy and thyroid scan are not needed for Hashimoto thyroiditis (a scan can help separate hashitoxicosis from Graves disease).
• Other findings: anaemia, raised cholesterol, raised CK.

Management

• Levothyroxine in a dose that normalises TSH and FT4.
• Children with Hashimoto thyroiditis who are still euthyroid need TSH and FT4 every 6 to 12 months.
• A goitre with normal TSH usually does not need treatment.

Prognosis and untreated complications

• Signs and symptoms resolve fully with treatment.
• No permanent intellectual damage, unlike untreated congenital hypothyroidism.
• Catch-up growth is good unless hypothyroidism starts near puberty when skeletal maturation is almost complete; long-standing disease can reduce adult height.
• Untreated: short stature, delayed puberty, poor school energy, and in severe cases effusions or myxoedema coma.

Hyperthyroidism

Aetiology

Graves disease: clinical features

• About 5 times commoner in girls; peak in adolescence; usually after 5 years; family history common.
• Insidious onset: emotional lability, falling school performance, poor concentration, poor sleep. It may be mistaken for a psychological problem.

Investigations

• FT4 and/or T3 raised, TSH suppressed.
• Occasionally only T3 is raised (T3 toxicosis).
• Raised radioactive iodine uptake (diffuse) in Graves disease; low uptake in thyroiditis.
• Anti-TPO and antithyroglobulin antibodies may also be present, usually at lower titre than in Hashimoto thyroiditis.

Management

Three options: drugs, radioiodine, surgery.

1. Antithyroid drugs (first-line in children)

• Methimazole (carbimazole is its precursor) is preferred. Nelson gives 0.4 to 0.6 mg per kg per day, as one or two doses.
• Propylthiouracil (PTU) is equally effective, but is no longer first-line because it can cause serious hepatotoxicity, even acute liver failure.
• A beta blocker (propranolol or atenolol) controls tremor and tachycardia until the antithyroid drug takes effect, then is tapered.
• Continue for about 1 to 2 years; remission is roughly 25% per year; the course can be repeated.
• Side effects: rash, muscle pain, jaundice, granulocytopenia (agranulocytosis). Agranulocytosis is sudden and occurs in the first months; check the blood count and stop the drug if white cells are low.
• Iodine suppresses the gland for only a few weeks; it is used before surgery, never long term.

2. Radioactive iodine (iodine-131)

• Slower; may need repeat doses; usually leads to permanent hypothyroidism, which is the intended end point (easier to treat than thyrotoxicosis).
• Contraindicated in pregnancy (destroys the fetal thyroid).

3. Surgery (subtotal or total thyroidectomy)

• For failure of, or poor adherence to, drug treatment.
• Risks: hypothyroidism or persistent hyperthyroidism, recurrent laryngeal nerve palsy, hypoparathyroidism (hypocalcaemia), keloid, thyroid storm.

Thyroid storm

• Rare emergency: high fever, marked tachycardia, hypertension, confusion or coma, heart failure, shock.
• Treatment: cooling, beta blocker, antithyroid drug first, then iodine, hydrocortisone for relative adrenal insufficiency, and diuretics and digoxin for heart failure.

Neonatal (congenital) hyperthyroidism

• Due to maternal TSH-receptor stimulating antibodies (IgG) crossing the placenta from a mother with Graves disease (even one treated before pregnancy).
• Can occur even if the mother was cured by surgery or radioiodine, because the antibodies persist.
• Onset may be delayed for several days if the mother was on antithyroid drugs, until the drug wears off.
• Features: irritability, tachycardia (may cause heart failure), poor feeding, failure to thrive, flushing, sweating, diarrhoea, hepatosplenomegaly, jaundice, thrombocytopenia, craniosynostosis, advanced bone age.
• Treatment: methimazole and a beta blocker if severe; mild cases can be observed.
• Self-limiting: clears by about 2 to 3 months as maternal antibodies decline.

Prognosis and follow-up

• Drug-treated children need regular FT4, TSH and blood counts, plus growth and pubertal checks.
• After surgery or radioiodine, patients often become hypothyroid (after surgery, many within 10 years) and need lifelong levothyroxine.

Quick revision

• Acquired = after first year; Hashimoto commonest; girls; after 6 years; peak adolescence.
• Firm non-tender goitre; euthyroid, hypothyroid or briefly hyperthyroid.
• Slow growth, weight gain, delayed bone age; TSH high, FT4 low; anti-TPO positive.
• Levothyroxine; euthyroid Hashimoto: TFTs every 6 to 12 months.
• Acquired hypothyroidism: no permanent brain damage; catch-up growth usually good.
• Graves: TSI; girls about 5:1; adolescents; school decline, weight loss, tremor, goitre, eye signs.
• FT4/T3 high, TSH suppressed.
• Methimazole first-line; PTU liver failure; beta blocker; agranulocytosis.
• Radioiodine: permanent hypothyroidism, not in pregnancy; surgery: nerve palsy, hypocalcaemia.
• Neonatal Graves: maternal antibodies, resolves by 2 to 3 months.

Written by The House Job from standard references (Basis of Paediatrics by Pervez Akbar; Nelson Essentials of Paediatrics).

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