Thyrotoxicosis

Disease Description (Causes and Symptoms)

• Definition: A condition in which systemic metabolic function is reduced due to insufficient thyroid hormones (mainly T4/T3).
• Main causes
  • Autoimmune thyroiditis (Hashimoto’s thyroiditis) — most common.
  • After thyroidectomy or radioactive iodine treatment.
  • Hypofunction following subacute (viral) or chronic thyroiditis.
  • Drug-induced (e.g., lithium, amiodarone, etc.).
  • Congenital defects.
  • Central (secondary) hypothyroidism: hypothalamic/pituitary diseases (tumors, infections, metastases, etc.).
• Pathophysiology summary: Decreased thyroid hormones → ↓ basal metabolic rate, abnormalities in protein, lipid, and carbohydrate metabolism, and reduced cardiovascular, gastrointestinal, and nervous system function. Depending on the cause, TSH is elevated (primary) or normal/decreased (central).
• Main symptoms
  • Fatigue, lethargy, weight gain (despite decreased appetite), sensitivity to cold, dry·pale skin, hair loss
  • Bradycardia, constipation, reduced memory and concentration, reduced exercise capacity
  • Voice changes (hoarseness), muscle pain·tingling, nonpitting edema (myxedema)
  • Women: heavy menstrual bleeding (menorrhagia), possible infertility
  • In severe cases: hyperlipidemia, worsening cardiovascular disease, coma (myxedema coma)

Treatment and Precautions

• Basic treatment
  • Standard treatment: Daily oral supplementation with synthetic T4 (levothyroxine).
  • Treatment principle: Lifelong supplementation is necessary in most cases, but recovery is possible after some cases of temporary thyroiditis.
  • Dose adjustment
    • Young adults without cardiovascular disease may receive the full initial dose (full replacement dose), depending on body weight, age, and underlying conditions.
    • In older adults or patients with coronary artery disease, starting with a low dose and gradually increasing it is recommended (e.g., increases of 12.5–25 μg at a time).
    • During pregnancy, requirements increase (generally a 20–30% increase from the baseline dose) — active treatment during pregnancy is necessary.
  • Monitoring: Measure TSH (and free T4) every 6–8 weeks after starting treatment or changing the dose; once the target range is reached, test every 6–12 months.
• Other treatments/tests
  • If autoimmune thyroiditis is suspected, antibody testing (anti-TPO, anti-thyroglobulin).
  • If nodules are suspected, ultrasound and, if necessary, biopsy.
  • If central hypothyroidism is suspected, pituitary evaluation (brain imaging and testing of other hormone axes).
• Lifestyle management
  • Levothyroxine is recommended on an empty stomach (30–60 minutes before breakfast). Alternatively, it may be taken 3–4 hours after bedtime.
  • Absorption may be reduced through interactions with antacids, calcium·iron supplements, antacid preparations, cholestyramine, etc. → The dosing interval needs to be adjusted (usually an interval of at least 4 hours).
  • Dose changes may be necessary due to increased TBG with estrogen medications or pregnancy.
• Precautions and risk of complications
  • Excessive dosing may cause a hyperthyroid state (palpitations, increased risk of osteoporosis).
  • If untreated, hyperlipidemia·atherosclerosis·worsening heart failure, infertility, reduced neurocognitive function, and, rarely, myxedema coma may occur.
  • Patients with cardiovascular disease need a lower starting dose and monitoring of their cardiac status.

Checklist Before an Outpatient Visit (Including Preparation Items and Example Questions)

• Preparation items
  • A list of all currently used medications and dietary supplements (including doses and administration times).
  • Copies of recent test results (TSH, free T4, antibody tests, thyroid ultrasound results, etc.).
  • A specific record of symptom changes (time of onset, patterns of worsening/improvement, and related circumstances).
  • History of thyroid surgery or radioactive iodine treatment, history of radiation exposure, whether pregnant or planning pregnancy, and history of heart disease.
• Examples of items that are useful for patients to record during an outpatient visit
  • Recent weight changes (kg), menstrual changes (women), degree of fatigue (impact on daily life), frequency of constipation, and sensitivity to cold.
  • Medication-taking patterns, including administration times (especially whether iron, calcium, or antacids are being taken).
• Example questions: Questions patients should prepare in advance for their doctor
  • "What do my current TSH and free T4 levels mean?"
  • "What is the plan for starting and increasing levothyroxine?"
  • "When should I take it, and how much time should I leave between it and other medications?"

General Example Questions to Ask the Doctor

• What are the common side effects of this medication (levothyroxine)? When should I contact the hospital?
• What is the target TSH range for treatment? How often should testing be performed?
• Is dose adjustment necessary during pregnancy or breastfeeding?
• Are there interactions with other medications (vitamins, antacids, antidepressants, etc.)?
• If my symptoms do not improve, what additional tests will be performed?

Examples of Disease-Specific Questions

• My anti-thyroid peroxidase antibody (anti-TPO) is positive. To what extent is thyroid function likely to change (worsen) in the future, and how often should follow-up testing be performed?
• A thyroid nodule was found (or I previously received radioactive iodine treatment). What is the plan for determining the cause of my current hypothyroidism and for additional tests (ultrasound, biopsy, uptake test, etc.)?