Hypothyroidism Lecture Notes

Introduction

• What is Hypothyroidism?
  • Condition with low thyroid hormone levels
  • Two types:
    • Primary: Thyroid gland is the problem
    • Secondary: Pituitary or hypothalamus is the problem

Primary Hypothyroidism

• Thyroid Hormone Production
  • Thyroid gland produces T3 (triiodothyronine) and T4 (thyroxine)
  • Hypothyroidism involves reduced production of these hormones
• Causes of Reduced Production
  • Destruction of thyroid follicular cells
    • Cannot produce thyroglobulin
    • Cannot combine thyroglobulin with iodine to form thyroid hormone
  • Iodine deficiency
    • Common worldwide cause of hypothyroidism
    • Insufficient iodine intake prevents formation of thyroid hormone

Causes of Primary Hypothyroidism

• Iodine Deficiency
  • Most common worldwide
  • Inadequate iodine prevents thyroid hormone production
• Thyroid Destruction
  • Autoimmune Thyroiditis: Antibodies against thyroglobulin or TPO (thyroid peroxidase)
    • Diseases: Hashimoto's, postpartum, IgG4-related
  • Infectious Thyroiditis: Triggered by viral infections
    • Example: De Quervain's thyroiditis (painful goiter)
  • Iatrogenic Causes: Surgical removal or radioiodine therapy
• Diagnostics
  • Primary: Low T3/T4, High TSH
  • Secondary: Low T3/T4, Low TSH

Secondary Hypothyroidism

• Causes
  • Pituitary adenoma (macroadenoma)
  • Sheehan's Syndrome (postpartum hemorrhage)
  • Traumatic brain injury
• Effect on Hormone Levels
  • Low TRH and TSH production
  • Results in reduced stimulation of the thyroid gland

Clinical Presentation

• Symptoms
  • Multi-system involvement
  • Common symptoms:
    • Goiter
    • Cold intolerance
    • Weight gain
    • Lethargy and fatigue
    • Delayed deep tendon reflexes
    • Bradycardia
    • Constipation
    • Dry skin, brittle hair & nails
• Severe Case: Myxedema Coma
  • Associated with stressors: Infection, surgery, hypothermia
  • Profound hypothermia, bradycardia, coma

Diagnosis

• Thyroid Function Tests (TFTs)
  • TSH and T4 measurements
• Primary vs. Secondary
  • Primary: High TSH, Low T4
  • Secondary: Low TSH, Low T4
• Subclinical Hypothyroidism
  • Elevated TSH, normal T4

Treatment

• General Approach
  • Levothyroxine (Synthroid) to replace thyroid hormone
• Myxedema Coma
  • IV T4 and T3 administration
  • Warming measures for hypothermia
  • Hydrocortisone for potential adrenal insufficiency

Conclusion

• Hypothyroidism encompasses a range of clinical features and requires careful diagnosis and management.
• Understanding the pathophysiology aids in distinguishing between primary and secondary types.
• Management focuses on hormone replacement and supportive care in severe cases.

Additional Resources

• For more detailed notes and illustrations, visit the provided website link in the video description.
• Practice questions and exam prep courses are also available on the website.