Thyroid disorders, differences in children and adults

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Introduction

Thyroid disorders are among the most common endocrine diseases and result from abnormalities in thyroid hormone production, secretion, or action. Because thyroid hormones profoundly influence growth, neurodevelopment, metabolism, and organ maturation, thyroid dysfunction in childhood presents differently than in adults and carries greater long-term consequences.

This article reviews the major thyroid disorders and highlights key differences between pediatric and adult presentations.

Physiology Overview

Thyroid hormone production is regulated through the hypothalamic–pituitary–thyroid (HPT) axis.

• Hypothalamus → TRH
• Pituitary → TSH
• Thyroid → T4 (thyroxine) and T3 (triiodothyronine)

Major functions of thyroid hormones:

• Metabolic rate regulation (↑ O₂ consumption, ↑ heat production)
• Growth and skeletal maturation
• Brain development (critical during fetal and early postnatal periods)
• Cardiovascular stimulation (↑ HR, ↑ contractility)
• Gastrointestinal motility
• Lipid and carbohydrate metabolism

Children are more dependent on thyroid hormone for **growth and neurodevelopment**, while adults mainly exhibit metabolic effects.

Hyperthyroidism

Hyperthyroidism is a state of excess thyroid hormone action at the tissue level.

Causes

• Graves disease (TSH receptor–stimulating antibodies)
• Toxic multinodular goiter
• Toxic adenoma
• Thyroiditis (transient hyperthyroid phase)
• Excess exogenous thyroid hormone

Clinical Manifestations

Adults:

• Heat intolerance
• Weight loss despite increased appetite
• Tremor, anxiety, irritability
• Palpitations, atrial fibrillation
• Hyperdefecation
• Muscle weakness

Children:

• Hyperactivity, emotional lability
• Rapid linear growth initially (can advance bone age)
• Decline in school performance
• Behavioral disturbances
• Tachycardia; risk of heart failure is higher in infants

Graves Disease

Autoimmune stimulation of TSH receptor. Features:

• Diffuse goiter
• Exophthalmos (mainly adults; rare but possible in adolescents)
• Pretibial myxedema (adults)

Hypothyroidism

Hypothyroidism is a deficiency of thyroid hormone production or action.

Causes

• Autoimmune thyroiditis (Hashimoto thyroiditis)
• Iodine deficiency
• Post-surgical or post-radioiodine
• Drugs (lithium, amiodarone)
• Congenital defects (thyroid dysgenesis, dyshormonogenesis)

Clinical Manifestations

Adults:

• Fatigue
• Weight gain
• Cold intolerance
• Constipation
• Bradycardia
• Hyperlipidemia
• Depression, cognitive slowing

Children:

• Growth retardation
• Delayed bone age
• Poor school performance
• Behavioral changes
• Cold intolerance, dry skin
• Pubertal delay

Congenital Hypothyroidism

Occurs due to thyroid dysgenesis, dyshormonogenesis, or TSH receptor defects. It is one of the most important causes of preventable intellectual disability.

Clinical Features

• Prolonged neonatal jaundice
• Feeding difficulties
• Lethargy
• Hypotonia
• Large tongue (macroglossia)
• Umbilical hernia
• Poor growth

Consequences

Without early treatment:

• Severe intellectual disability
• Growth failure
• Motor developmental delay

Newborn screening programs detect elevated TSH → enabling early therapy.

Neonatal Hyperthyroidism

Usually caused by transplacental passage of maternal TSH receptor–stimulating antibodies (in mothers with Graves disease).

Clinical Features

• Irritability
• Tachycardia
• Hypertension
• Poor weight gain
• Craniosynostosis (if prolonged)
• Heart failure in severe cases

Condition is transient and resolves as maternal antibodies disappear.

Goiter

Goiter is enlargement of the thyroid gland.

Causes

• Iodine deficiency
• Autoimmune thyroiditis (Hashimoto, Graves)
• Nodular hyperplasia
• Dyshormonogenesis (children)
• Goitrogen exposure

Differences

• In adults → often nodular, may produce hyperthyroidism
• In children → often diffuse; may indicate autoimmune disease or congenital enzyme defects

Thyroiditis

Hashimoto Thyroiditis

Autoimmune destruction of thyroid tissue → hypothyroidism.

Features:

• Firm, rubbery goiter
• Presence of anti-TPO and anti-TG antibodies

More common in adolescents than younger children.

Subacute (De Quervain) Thyroiditis

Painful thyroid enlargement following viral illness. Transient hyperthyroidism → hypothyroidism → recovery.

Diagnostic Evaluation

• Serum TSH (primary marker)
• Free T4, total T3
• Thyroid antibodies (anti-TPO, anti-TG, TRAb)
• Thyroid ultrasound
• Radioiodine uptake scan (adults; rarely in children)
• Bone age assessment (in pediatric hypothyroidism or hyperthyroidism)

Key Differences Between Thyroid Disorders in Children and Adults

Feature	Children	Adults
Importance of thyroid hormone	Critical for **brain development** and **growth**	Mainly regulates metabolism and cardiovascular function
Hyperthyroidism presentation	Hyperactivity, behavioral issues, rapid growth, tachycardia	Weight loss, heat intolerance, tremor, atrial fibrillation
Hypothyroidism presentation	Growth retardation, delayed puberty, poor school performance	Fatigue, weight gain, constipation, depression
Congenital disorders	Common (dysgenesis, dyshormonogenesis)	Rare
Goiter features	Often diffuse (autoimmune, dyshormonogenesis)	Often nodular (multinodular goiter)
Long-term consequences	Severe developmental delay if untreated congenital hypothyroidism	Metabolic and cardiovascular complications

Illustrations

1. Overview of Thyroid Hormone Physiology

Overview of thyroid hormone synthesis and regulation.

2. Graves Disease

Mechanism of TSH receptor–stimulating antibodies in Graves disease.

3. Hashimoto Thyroiditis

Lymphocytic infiltration and germinal centers characteristic of Hashimoto thyroiditis.

4. Cretinism / Congenital Hypothyroidism

Consequences of untreated congenital hypothyroidism.

Summary

Thyroid disorders affect children and adults differently due to the essential role of thyroid hormones in neurodevelopment and growth. Hyperthyroidism in children often presents with behavioral and growth abnormalities, whereas adults exhibit classic metabolic symptoms. Hypothyroidism in children causes growth retardation and cognitive impairment, while adults experience fatigue, weight gain, and metabolic slowing. Congenital hypothyroidism poses the greatest risk, requiring early detection and treatment to prevent irreversible developmental damage.

Sources

• Jameson JL, De Groot LJ. *Endocrinology: Adult and Pediatric*, 7th Edition. Elsevier.
  • Chapter 74: Thyroid Physiology
  • Chapter 75: Hyperthyroidism
  • Chapter 76: Hypothyroidism and Thyroiditis
  • Chapter 80: Thyroid Disorders in Children

• Melmed S, Auchus RJ, Goldfine AB, Koenig RJ, Rosen CJ. *Williams Textbook of Endocrinology*, 14th Edition. Elsevier.
  • Chapter 11: Hypothalamic–Pituitary–Thyroid Axis
  • Chapter 12: Disorders of the Thyroid in Adults
  • Chapter 13: Thyroid Function in Growth and Development (Pediatrics)

• Brent GA, Davies TF. *Thyroid Disease Management*. New England Journal of Medicine Review Articles.
  • Pathophysiology of Graves Disease
  • Autoimmune Thyroiditis mechanisms

• Ross DS et al. American Thyroid Association Guidelines.
  • Management of Hyperthyroidism and Graves Disease
  • Guidelines for Screening and Treatment of Congenital Hypothyroidism

• Robbins and Cotran. *Pathologic Basis of Disease*, 10th Edition. Elsevier.
  • Chapter 24: The Endocrine System (Thyroid Disorders)

• Guyton AC, Hall JE. *Textbook of Medical Physiology*, 14th Edition.
  • Chapter 76: Thyroid Metabolic Hormones
  • Effects on Growth and Development

• Larsen PR, Kronenberg HM. *Williams Manual of Endocrinology*, 9th Edition.
  • Pediatric and Adult Thyroid Disorders Overview