Thyroid Physiology and Hormone Regulation Quiz

Thyroid Disorders in Children

• Thyroid disorders are a significant concern in children, affecting growth, development, and metabolism.
• The thyroid gland is located in the middle of the neck, beneath the thyroid cartilage.
• The gland comprises two lobes, an isthmus, and sometimes a pyramidal lobe. These lobes originate from different embryonic sources.
• Thyroid hormones (T3 and T4) are crucial for regulating growth, development, metabolism, and body temperature. They are synthesized within the follicular cells of the thyroid gland.
• Iodine uptake is the first step in thyroid hormone synthesis. Iodine is transported into the follicular cell by a sodium-iodide transporter.
• Inorganic iodine is then transported to the basolateral surface by the protein pendrin, and organified by the enzymes thyroid peroxidase (TPO) and Dual oxidase 2 (Duox2).
• Organified iodine is incorporated into thyroglobulin, combining with tyrosine to form monoiodotyrosine (MIT) and diiodotyrosine (DIT).
• Two DIT molecules fuse to create thyroxine (T4), while one DIT and one MIT combine to form triiodothyronine (T3).
• Ninety percent of circulating T4 and 20-30% of T3 is directly produced by the thyroid gland. Remaining T3 is generated from peripheral conversion of T4 by the enzyme monodeiodinase I (MDI).
• Free T4 and T3 circulate bound to proteins (TBG, albumin, transthyretin).
• T4 is primarily bound to TBG, while T3 binds to all three.
• Thyroid hormone metabolism involves the conversion of T4 to T3, and their inactivation to reverse T3 (rT3) and T2 by type 3 MDI in target tissues.
• T3 is the active thyroid hormone, entering cells and binding to intracellular receptors to regulate gene expression.
• Thyroid hormone production and release in the body is controlled by TSH, secreted by pituitary thyrotropes acting on TSH receptors. This regulates iodine uptake, organification, coupling, and hormone release. Also regulates follicular development.
• TSH secretion controlled by the hypothalamic hormone, TRH (thyrotropin-releasing hormone).
• Thyroid function assessment in a child includes clinical evaluation and assessment of thyroid function and structure. A full history and examination are important.
• Common symptoms of hypothyroidism in children include weakness, lethargy, weight gain, somnolence, facial puffiness, decreased performance, and decreased activity/ hypotonia.
• Symptoms of hyperthyroidism in children include weight loss, anxiety, tremors, eye protrusion, neck swelling, and the presence of type 1 diabetes mellitus or celiac disease.
• Thyroid examination typically assesses size, mobility, and consistency. The presence of a goiter may indicate further testing.
• Thyroid function tests—TSH, T4, and potentially T3—are used to evaluate thyroid dysfunction. Free T4 is a more consistent indicator than total T4.
• Congenital hypothyroidism (CH) is the most common congenital endocrine disorder in childhood and is largely preventable. It is defined as thyroid hormone deficiency present at birth, with approximately 1 case per 1500 live births.
• Causes of CH include thyroid dysgenesis, dyshormonogenesis, TSH resistance, transient hypothyroidism, and peripheral hypothyroidism.
• Secondary (central) hypothyroidism arises from pituitary or hypothalamic abnormalities, characterized by low/inappropriately normal TSH with low free T4. Causes include CNS insult, tumor, radiation, or trauma.
• Primary hypothyroidism is diagnosed by the presence of elevated TSH levels with low or normal T4 levels. Common causes include ectopic thyroid, genetic defects, or dyshormonogenesis.
• Treatment for hypothyroidism typically involves levothyroxine replacement therapy, with careful monitoring of free T4 and TSH levels. Dose adjustment is often necessary.

Acquired Hypothyroidism

• Subclinical hypothyroidism is frequently experienced by adolescents.
• Causes of acquired hypothyroidism include chronic lymphocytic (Hashimoto's) thyroiditis, iodine deficiency, medications and post-radiation or ablative (radioiodine therapy or surgery).
• Symptoms, physical examination, and investigations aid in diagnosis.

Thyrotoxicosis in Children

• Thyrotoxicosis, while rare in children is important to identify. It generally is characterized by an increased production of thyroid hormones, leading to clinical manifestations like weight loss, hyperdefection (often associated with increased urination-polyuria) , tremors, anxiety, irritability, and worsening school performance.
• Causes of thyrotoxicosis include TSH receptor activating mutations, toxic thyroid nodules, toxic multinodular goiter, subacute lymphocytic (granulomatous) thyroiditis, and acute thyroiditis.
• Graves' disease is a common cause of thyrotoxicosis, predominantly in females affecting most children who present with symptoms.
• Diagnosing thyrotoxicosis involves identifying the cause, evaluating complications, and considering a comprehensive clinical and laboratory evaluation, including thyroid function tests (TFTs), erythrocyte sedimentation rate (ESR), and potentially antibodies (e.g., TSH receptor antibodies).
• Management strategies for thyrotoxicosis may include antithyroid drugs, radioactive iodine, or surgery, adjusting the strategy based on child characteristics.
• Monitoring is critical; after treatment the thyroid profile needs to monitored for 6 weeks and then monthly to ensure proper response to the treatment and prevent complications.

Congenital Hypothyroidism (CH) Assessment

• Evaluation of newborns for hypothyroidism (neonatal screening) is essential.
• Screening for CH typically involves measuring TSH levels—high TSH levels suggest a need for further evaluation.
• Typical presentation involves certain signs and symptoms and physical characteristics if diagnosed at an early age or later ages.
• Confirmation of the diagnosis involves assessing underlying factors. If no improvement or the disorder is prolonged, confirmatory medical procedures may be required.

Monitoring of Thyroid Function

• Monitoring of thyroid hormone levels (free T4 and TSH) is vital throughout treatment to maintain appropriate levels.
• Adjustments to medication doses are typically needed to maintain the proper target levels of free thyroxine. This requires accurate tracking and frequent dosage adjustments.
• Persistent monitoring of thyroid function tests is essential after treatment, with appropriate dosage adjustments.

This quiz focuses on key concepts related to thyroid physiology, hormone synthesis, and the assessment of thyroid function. It covers various tests, the role of thyroid hormones, and developmental factors related to the thyroid gland. Assess your knowledge about this critical endocrine system.