Overactive thyroid

Disease Description (Causes and Symptoms)

• Definition: A condition in which the secretion of thyroid hormones (T4, T3) is insufficient, resulting in decreased systemic metabolic rate and organ function (hypothyroidism).
• Main causes
  • Autoimmune thyroiditis (Hashimoto’s thyroiditis) — most common
  • Loss of thyroid tissue after thyroid surgery or radioactive iodine treatment
  • Thyroid inflammation/viral thyroiditis (some cases are temporary)
  • Congenital thyroid developmental abnormalities
  • Central (hypothalamic–pituitary) hypothyroidism — decreased TSH secretion (tumors, infections, metastases, etc.)
  • Medications (lithium, amiodarone, etc.) or severe iodine deficiency/excess
• Summary of pathophysiology: Thyroid hormone deficiency → decreased basal metabolic rate, changes in protein, lipid, and carbohydrate metabolism, nonpitting edema (myxedema) caused by glycosaminoglycan accumulation, decreased heart rate and cardiac output, etc.
• Common symptoms
  • Fatigue, lethargy, sensitivity to cold, weight gain (despite decreased appetite)
  • Dry, pale skin; hair loss; a low-pitched voice; slowed speech and thinking
  • Constipation, muscle pain and malaise, swelling of the hands and feet (nonpitting, myxedema)
  • In women, increased menstrual bleeding or amenorrhea may occur
  • Cardiovascular system: bradycardia, elevated cholesterol, decreased cardiac function
• Severe complication: Shock, hypothermia, and coma (myxedema coma) are medical emergencies

Treatment Methods

• Goal: Restore a normalized thyroid hormone state (improvement of symptoms and appropriate biochemical indicators).
• Drug therapy
  • Basic treatment: Oral supplementation with levothyroxine (Levothyroxine, L-T4) — once daily
    • Usual full replacement dose: approximately 1.6 μg/kg/day (in young adults without cardiovascular disease)
    • Older adults or patients with cardiovascular disease should start with a low dose (e.g., 12.5–25 μg/day) and increase it at 6–8-week intervals
    • After adjusting the dose, evaluate the response using TSH (or free T4 in central hypothyroidism)
  • T3 (liothyronine): Used rarely as short-term supplementation or in specific situations. Monotherapy is generally not recommended.
  • Central hypothyroidism: Because TSH is not useful, adjust the dose based on free T4.
• Emergency treatment
  • Myxedema coma: Treatment in the emergency department or intensive care unit, administration of IV levothyroxine (intravenous), warming, maintenance of respiratory and hemodynamic function, correction of infection, hypoglycemia, hyponatremia, and other abnormalities, and administration of steroids (when adrenal function is uncertain).
• Lifestyle management and precautions
  • How to take it: Take on an empty stomach (recommended 30–60 minutes before breakfast) (or 3–4 hours after bedtime) — maintain an interval from foods and products that affect absorption (at least 4 hours for calcium, iron, antacids, etc.)
  • Drug interactions: Calcium, iron, antacids, plant-based fiber, soy-containing products, and some PPIs may reduce absorption; interactions with warfarin, diabetes medications, and others are possible (monitoring is required)
  • Pregnancy: An increase of approximately 20–30% in the dose is generally needed once pregnancy is confirmed (regular TSH testing is required)
• Follow-up testing
  • Test TSH at 6–8-week intervals after starting treatment or changing the dose. Once stable, test every 6–12 months.
  • Manage central hypothyroidism using free T4.
• Preventive/nonpharmacological treatment
  • Treat the cause (e.g., supplementation after surgery and treatment of pituitary disease causing central hypothyroidism)
  • Lipid management and management of cardiovascular risk factors

Checkpoints Before an Outpatient Visit (What to Prepare and Example Questions)

• What to prepare
  • A list of all medications and health supplements currently being taken (including doses and dosing times)
  • Previous blood test results (TSH, free T4, antibody test results, etc.) and thyroid ultrasound or biopsy results, if available
  • A record of when symptoms began and how they have changed (weight, fatigue, sensitivity to cold, constipation, etc.)
  • Whether pregnancy is possible, plans for pregnancy, and whether you are breastfeeding
  • History of thyroid surgery or radioactive iodine treatment and any other history of radiation exposure
• Information commonly checked by doctors during an outpatient visit for diagnosis and follow-up
  • Current use of warfarin or other anticoagulants, cardiovascular medications, iron products, calcium supplements, etc.
  • History of cardiovascular disease (angina, myocardial infarction, heart failure, etc.)
  • History of allergies or adverse drug reactions

General Example Questions to Ask the Doctor

• What are the expected side effects of this medication (levothyroxine), and how should I manage them?
• What is the treatment goal (target TSH range)? How long will I need follow-up testing after starting treatment?
• What are the recommendations regarding when and how to take the medication (on an empty stomach and the interval from meals)?
• Can I take it together with other medications (e.g., iron supplements, calcium supplements, antacids, or warfarin)? Is any adjustment needed?
• How should it be managed during pregnancy (or when planning a pregnancy)?

Examples of Condition-Specific Questions

• I am planning to become pregnant. How should my thyroid hormone dose be adjusted, and what is the target TSH level?
• I am currently taking warfarin. How should INR be managed when starting levothyroxine treatment or changing its dose?

(If needed, providing test results and information about your medications can help us organize more specific points for consultation.)