Hyperthyroidism (Graves' Disease)

Hyperthyroidism

  • Second half of thyroid disorders.
  • Focus on pathophysiology, clinical manifestations, and management.
  • Graves' disease is a key manifestation.
  • Textbook readings: 492-494.

Definition

  • Elevated levels of thyroid hormones.

Causes

  • Most common cause: Autoimmune process linked to Graves' disease (similar to Hashimoto's in hypothyroidism).
  • Higher incidence in women, familial component.

Factors Associated with Onset

  • Major life change, especially in females:
    • Menopause (changes in estrogen levels)
    • Pregnancy (hormonal changes)
    • Menarche (first menstruation)
  • Bacterial infections: Yersinia enterocolitica.
  • Vitamin D deficiency.
  • Tumor development on the pituitary or thyroid gland (influences thyroid hormone production).
  • Excessive iodine availability: Increased iodine leads to increased T3 and T4 production.

Thyroid Storm

  • Rare due to increased monitoring.
  • Sudden increase in circulating thyroid hormone, leading to a hypermetabolic state.
  • Triggers:
    • Significant illnesses
    • Pregnancy
    • Surgery
    • Sudden reduction or stopping of anti-thyroid medication.
  • Can be fatal; requires rapid intervention.
  • Symptoms:
    • Increased heart rate
    • Elevated blood pressure
    • Hyperthermia (elevated body temperature)

Pathophysiology of Graves' Disease

  • Autoimmune basis.
  • Abnormal antibodies are formed (thyroid stimulating antibodies).
  • These antibodies bind to thyroid stimulating hormone (TSH) receptors on the thyroid gland.
  • The thyroid stimulating antibodies compete with TSH for the receptors.
  • Binding of antibodies stimulates continuous release of thyroid hormone.
  • Excessive hormone release leads to clinical features of hyperthyroidism.

Clinical Manifestations

  • Metabolic rate increases.
  • Heart rate: Tachycardia (rapid heart rate), palpitations, angina-like sensations.
  • Muscle weakness and fatigue (due to overstimulation).
  • Increased gastrointestinal mobility.
  • Heat intolerance.
  • Increased appetite, potential weight loss (hypermetabolic state).
  • Nervousness, tremors, hyperreflexia (overactive reflexes), insomnia.

Graves' Disease Specific Manifestation

  • Exophthalmos: Bulging eyes due to inflammation around the eyes.
    • Autoantibody-induced inflammation.
    • Increased connective tissue behind the eye.
    • Difficulties blinking or closing eyes; requires moisture to prevent dryness.

Management of Hyperthyroidism

  • Anti-thyroid medication (usually first choice).
  • Radioactive isotopes (more common in America; Australia uses medicine first).
  • Surgery (less common).

Radioactive Isotopes:

  • Treat toxic thyroid adenoma, multi nodular goiter.
  • Used for Graves' disease relapse.
  • More common in older people.
  • Destroys thyroid tissue, which can lead to hypothyroidism.
  • Usually a one-off dose.

Surgery:

  • Used when other treatments aren't suitable:
    • Pregnancy (radioactive isotopes contraindicated).
    • Allergies to anti-thyroid medicines.
    • Extremely large goiters.
    • Severe exophthalmos.

Anti-Thyroid Medicines:

  • Carbimazole is the main option in Australia for patient I know.
  • Reduces circulating levels of thyroid hormone.
  • Prevents iodine from being incorporated into the hormone structure (T3 and T4).
  • Inhibits the formation and release of thyroid hormones.
  • Adverse effects:
    • Pruritus and rashes (early stages, may settle).
    • Rare but significant: Agranulocytosis (requires quick action if fever, mouth ulcers, rash, sore throat occur).
  • Takes 3-4 weeks to see clinical benefits due to stored hormones in the thyroid gland.
  • During pregnancy, propylthiouracil is preferred instead of carbimazole.
  • Once normal thyroid function is established, dosage is reduced to the lowest possible level.
  • Regular checks are needed to maintain control.

Comparison

  • Comparison of Hyperthyroidism vs. Hypothyroidism: Key to differentiation is to consider the effects of 'slowing down' vs 'speeding up' of the metabolism.