Hypothyroidism Lecture Notes

Exam Focus

• All exam questions will derive from the objectives listed in the lecture.

Anatomy and Function of the Thyroid Gland

• Location: Butterfly-shaped gland in the neck, below the larynx, in front of the trachea.
• Function: Produces thyroid hormones (T3 and T4).
  • Regulate metabolism
  • Influence on development and growth
  • Protein, fat, and carbohydrate metabolism
  • Regulate body temperature and menstrual cycle
  • Affect cardiac/nervous system functions, muscle strength, weight

Thyroid Hormone Production and Regulation

• Production: Hypothalamus releases TRH, which signals the anterior pituitary to secrete TSH. TSH signals the thyroid gland to release T3 and T4.
• Regulation: Negative feedback loop
  • High T3/T4 levels inhibit TRH and TSH release.
  • Low T3/T4 levels stimulate TRH and TSH release.
• Monitoring: TSH, T3, and T4 are closely monitored in thyroid disorders.

Hypothyroidism Overview

• Definition: Deficiency of thyroid hormones due to an underactive thyroid gland.
• Diagnosis: Low T4 and elevated TSH levels.
• Demographics: More common in females and elderly patients.

Signs and Symptoms

• Fatigue
• Cold intolerance
• Weight gain
• Various other symptoms due to slowing metabolism

Causes of Hypothyroidism

1. Hashimoto’s Disease: Autoimmune condition where antibodies attack the thyroid gland.
2. Surgical Removal: Of part or the whole thyroid gland.
3. Radiation Treatment: Damages the thyroid gland.
4. Medications: (e.g., Amiodarone, Lithium, Carbamazepine, Phenytoin).
5. Iodine Deficiency: Thyroid needs iodine to function.
6. Congenital Hypothyroidism: Absent or undeveloped thyroid gland.

Goals of Therapy

1. Improve clinical signs and symptoms.
2. Reach normal TSH levels.
3. Avoid overtreatment and side effects.

Treatment Options

• Levothyroxine (Synthroid)
  • Synthetic form of T4.
  • Most common treatment option.
  • Symptoms improve in 2-3 weeks; TSH levels regulate in 4-6 weeks.
  • Rare side effects if dosing is correct. Overdose can lead to hyperthyroidism symptoms.
  • Contraindications: Uncorrected adrenal insufficiency, uncontrolled cardiovascular diseases, not for obesity or weight reduction.
  • Monitoring: TSH levels every 4-6 weeks initially, then every 4-6 months, and annually if stable.
  • Administration: Taken with water, on an empty stomach, 1 hour before breakfast or at bedtime, 4 hours apart from antacids, iron, or calcium supplements.
  • Tablets are color-coded based on strength.
• Other Options
  • Armor Thyroid: Combination of T3 and T4
  • Liothyronine: T3 hormone replacement

Safety and Administration

• Key Points for Levothyroxine Administration
  • Take with water at the same time each day.
  • On an empty stomach, either 1 hour before breakfast or at bedtime, 3+ hours after the last meal.
  • Separate from antacids, iron, or calcium supplements by 4 hours.
  • Color-coded tablets based on strength.

Conclusion

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