Thyroid Disorders Notes

Anatomy of the Thyroid

  • Epiglottis
  • Hyoid Bone
  • Larynx (Thyroid Cartilage)
  • Pyramidal Lobe
  • Thyroid Gland
    • Lateral Lobes
    • Isthmus of Thyroid Gland
  • Trachea

Thyroid Physiology

  • Thyroid Hormones:
    • T3 (liothyronine): Active thyroid hormone with profound effects.
    • T4 (levothyroxine): Precursor to T3, synthesized from iodine.
  • Functions: Regulation of metabolism, cardiac function, growth, and development.
  • Hormone Regulation: Controlled by the hypothalamus and anterior pituitary.
  • Iodine Deficiency: Impacts thyroid function significantly.

Thyroid Hormone Actions

  • Effects on Metabolism: Increases basal metabolic rate.
  • Cardiac Function: Enhances heart rate and contractility.
  • Growth: Essential for normal growth in infancy and childhood.

Thyroid Function Tests

  • Serum TSH: Screening and diagnosis tool for hypothyroidism. Elevated levels indicate hypothyroidism.
  • Serum T4 Test: Measures total or free T4 levels in the blood.
  • Serum T3 Test: Measures total or free T3 levels; used in diagnosis and management of thyroid disorders.

Hypothyroidism

  • Description: Severe deficiency of thyroid hormone leading to various symptoms.
  • Types:
    • Myxedema in adults: Lifelong replacement therapy necessary.
    • Congenital Hypothyroidism: Replacement therapy essential from infancy.
Clinical Presentation in Adults
  • Pale, puffy, expressionless face.
  • Cold, dry skin.
  • Brittle hair or hair loss.
  • Reduced heart rate and body temperature.
  • Symptoms of lethargy and fatigue.
  • Cold intolerance.
  • Cognitive impairment.
Causes of Hypothyroidism
  • Malfunction of the thyroid gland (e.g., Hashimoto's disease).
  • Iodine deficiency.
  • Surgical removal or destruction of thyroid tissue (radioactive iodine).
  • Insufficient secretion of TSH and thyrotropin-releasing hormone (TRH).
Treatment of Hypothyroidism
  • Lifelong Replacement Therapy:
    • Levothyroxine (T4): Standard treatment.
    • Liothyronine (T3): Alternative or adjunct option.
Life Span Issues with Hypothyroidism
  • During Pregnancy: May cause neuropsychologic deficits in the child, especially in the first trimester.
  • In Infants: Can lead to growth derangements and possible mental retardation.

Hyperthyroidism

  • Forms:
    • Graves’ Disease: Most common; affects women aged 20-40. Symptoms include exophthalmos.
    • Toxic Nodular Goiter (Plummer’s Disease).
Causes of Hyperthyroidism
  • Thyroid-stimulating immunoglobulins (TSIs).
  • Treatment includes:
    • Surgical removal of thyroid tissue.
    • Destruction of thyroid tissue.
    • Suppression of hormone synthesis (e.g., beta-blockers, nonradioactive iodine).
Thyrotoxic Crisis (Thyroid Storm)
  • Causes: Significant stress in patients with thyrotoxicosis (e.g., surgery, illness).
  • Signs:
    • Hyperthermia (above 105°F), severe tachycardia, restlessness, agitation.
    • Symptoms can escalate to unconsciousness, coma, hypotension, or heart failure.
  • Treatment: Potassium iodide, Methimazole, beta blockers, sedation, glucocorticoids, IV fluids.
Methimazole (Tapazole)
  • First-line medication for hyperthyroidism.
  • Prototype thionamide; does not cause liver damage like PTU.
  • Takes 3-12 weeks for effective thyroid state recovery; contraindicated in the first trimester of pregnancy.
Levothyroxine (Synthroid)
  • Type: Synthetic preparation of thyroxine (T4); drug of choice for hypothyroidism.
  • Half-life: 7 days.
  • Administration: Take in the morning, 30-60 minutes before breakfast.
  • Adverse Effects: Tachycardia, angina, tremors; may intensify effects of anticoagulants like warfarin.
Propylthiouracil (PTU)
  • Inhibits synthesis of thyroid hormone; used as a second-line treatment for Graves’ disease.
  • Half-life: Approximately 90 minutes.
  • Adverse Effects: Can cause agranulocytosis, hypothyroidism, and severe liver damage.
Comparison of PTU and Methimazole
  • PTU causes liver injury; shorter half-life requiring multiple daily doses.
  • PTU less likely to cross placenta than methimazole.
  • PTU blocks T4 conversion to T3, whereas methimazole does not.
Radioactive Iodine-131 (131I)
  • Description: Radioactive isotope of iodine; used to affect thyroid function in cases of hyperthyroidism.
  • Half-life: 8 days; therapeutic effects may take 2-3 months to manifest.
Nonradioactive Iodine (Lugol's Solution)
  • Used preoperatively to suppress thyroid function.
  • Possible mild toxicity includes a brassy taste, burning sensations, and GI injury.
Beta Blockers
  • Used to control symptoms of tachycardia and anxiety in hyperthyroidism; beneficial during thyrotoxic crisis.