Hypothyroidism Lecture Notes

Introduction

• Presenter: Tom from Zero to Finals
• Topic: Hypothyroidism
• Additional resources: Notes available at Zero to Finals

Causes of Hypothyroidism

Common Causes

• Developed World: Hashimoto's Thyroiditis
  • Autoimmune inflammation of the thyroid gland
  • Associated with anti-thyroid peroxidase (anti-TPO) antibodies
  • Associated with anti-thyroglobulin antibodies
  • Initially causes a goiter, followed by atrophy of the thyroid
• Developing World: Iodine Deficiency
  • Essential for thyroid hormone production
  • Prevention through iodine addition to foods like table salt

Treatment-Related Causes

• Hypothyroidism can result from treatments for hyperthyroidism:
  • Carbimazole
  • Propylthiouracil
  • Radioactive iodine
  • Thyroid surgery

Medication-Induced Causes

• Lithium: Inhibits thyroid hormone production, can cause goiter and hypothyroidism
• Amiodarone: Interferes with thyroid hormone production and metabolism; typically causes hyperthyroidism, but can cause thyrotoxicosis

Secondary Causes (Central Causes)

• Pituitary gland fails to produce enough TSH
  • Often associated with hypopituitarism
  • Causes include:
    • Tumors
    • Infections
    • Vascular pathology (e.g., Sheehan syndrome)
    • Radiation therapy

Presentation of Hypothyroidism

• Symptoms:
  • Weight gain
  • Fatigue
  • Dry skin, coarse hair, hair loss
  • Fluid retention (edema, pleural effusions, ascites)
  • Amenorrhea
  • Constipation

Investigating Hypothyroidism

• Primary Hypothyroidism:
  • Low T3 and T4 levels
  • High TSH level (due to lack of negative feedback)
• Secondary Hypothyroidism:
  • Low TSH level
  • Low thyroid hormones

Management of Hypothyroidism

• Replace thyroid hormone with oral levothyroxine (synthetic T4)
• Levothyroxine metabolizes to T3 in the body
• Adjust doses based on TSH levels:
  • Measure TSH monthly until levels stabilize
  • High TSH: Increase dose
  • Low TSH: Decrease dose

Additional Resources

• Zero to Finals Website: Additional notes, illustrations, and test questions
• Blog: Career advice and tips on succeeding as a doctor
• YouTube Channel: Subscribe for updates on new videos

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