Disorders of the Thyroid in Childhood and Adolescence

Abstract

Disorders of the thyroid are one of the most common endocrinopathies in childhood and adolescence. The thyroid hormone is not only essential for metabolism and organ function but also plays a key role in the regulation of myelination of the nervous system. It is therefore crucial for normal growth and development in children. Thyroid hormone release is regulated by the hypothalamus and the pituitary gland. Therefore problems in thyroid hormones can occur as a result of disruption in the hypothalamo-pituitary-thyroid axis at any level.

Problems with the thyroid axis usually manifest as an underactive (hypothyroidism) or an overactive (hyperthyroidism) gland. The most common cause of an underactive thyroid in children is congenital hypothyroidism (CHT) followed by autoimmune hypothyroidism or Hashimoto’s thyroiditis (HT), the incidence of which peaks in adolescence. Introduction of the newborn screening test for CHT has facilitated early diagnosis and treatment of CHT improving outcome related to intellectual disability. Other rare causes of hypothyroidism include TSH deficiency in cases of secondary hypothyroidism which can be part of multiple pituitary hormone deficiency or rarely isolated. Hypothyroidism can also occur following surgical removal of the gland for Graves’ disease or damage following radiotherapy for cancer treatment.

The most common cause of hyperthyroidism is Graves’ disease which is treated with anti-thyroid drugs (ATDs) in a block and replace or dose titration regimen. The right approach is heavily debated in the medical field. ATD treatment is followed by definitive treatment with surgery or radioactive iodine if the patient relapses after stopping ATD. Another rare but serious cause of hyperthyroidism which carries a significant mortality rate if undiagnosed is neonatal thyrotoxicosis (NT). NT occurs in babies born to mothers with Graves’ disease or HT. This is a transient condition which may require treatment with ATDs. Hyperthyroidism can result from thyroid nodules such as toxic adenoma or multinodular goitre or rarely following radiotherapy and in McCune Albright syndrome.

Thyroid nodules can present as underactive or overactive thyroid but most frequently are not associated with thyroid dysfunction. Careful evaluation of nodules is critical due to the higher risk of these being cancerous in children compared with adults. Thyroid cancers can occur independently or as part of multiple endocrine neoplasias or familial neoplasias. Papillary thyroid carcinoma is the most common form of paediatric thyroid cancer. Other rare forms include follicular thyroid carcinoma and medullary thyroid carcinoma. It is important to consider the occurrence of thyroid cancers as part of multiple endocrine neoplasias.

Thyroid disorders are a common endocrinopathy in children and adolescents. Good clinical history and family history are vital in diagnosis, surveillance and planning follow-up in these patients.