Disease Description (Causes and Symptoms)
- Definition summary: A condition in which systemic metabolic activity decreases due to insufficient secretion of thyroid hormones (mainly T4/T3).
- Main causes
- Problems with the thyroid gland itself (primary): Hashimoto’s (autoimmune) thyroiditis, thyroidectomy, radioactive iodine treatment, congenital defects, and the recovery phase after subacute (viral) thyroiditis
- Central (secondary/tertiary): abnormalities of the pituitary gland (low TSH) or hypothalamus (tumors, infections, metastases, etc.)
- Pathophysiology summary
- Decreased thyroid hormones → decreased basal metabolic rate, decreased heat production, and abnormalities in protein synthesis and lipid and carbohydrate metabolism
- Nonpitting edema due to myxedema (mucopolysaccharidosis), elevated cholesterol, bradycardia, decreased cardiac function, etc.
- Typical symptoms
- Fatigue and lethargy, weight gain (possibly accompanied by decreased appetite), sensitivity to cold, dry and pale skin, hair changes
- Voice changes (hoarseness), muscle pain and cramps, constipation, heavy menstrual bleeding (women), generalized edema (nonpitting)
- Laboratory findings: in primary hypothyroidism, elevated TSH + decreased free T4; in central hypothyroidism, normal/decreased TSH + decreased free T4
- Severe complications: myxedema coma (acute and potentially fatal), cardiovascular complications (heart failure, myocardial ischemia), and atherosclerosis related to hyperlipidemia
Treatment Methods and Precautions
- Basic principle: Replace the deficient thyroid hormones at an appropriate dose (replacement therapy)
- First-line drug treatment
- Oral levothyroxine (T4) is the standard treatment
- Recommended starting doses (general guidelines)
- Young adults without cardiovascular disease: approximately 1.6 µg/kg/day (replacement dose)
- Older adults (>60–65 years) or patients with coronary artery disease: start with a low dose of 12.5–25 µg/day and increase gradually
- During pregnancy: an increase of approximately 25–30% immediately after pregnancy is confirmed is common (follow the doctor’s instructions)
- Monitoring: Test TSH (and free T4 if necessary) every 6–8 weeks after starting treatment or changing the dose. Once stabilized, annual testing is recommended (more frequently in special circumstances)
- Central (pituitary) hypothyroidism
- Because TSH is unreliable, adjust the dose based on free T4
- Temporary hypothyroidism (subacute or transient thyroiditis)
- Recovery is possible, so consider discontinuing the medication if it is no longer necessary after regular follow-up
- Emergency treatment (myxedema coma)
- IV levothyroxine (e.g., an initial 200–400 µg IV loading dose followed by 50–100 µg daily) ± low-dose T3 (liothyronine) supplementation (depending on the clinical situation), along with IV glucocorticoids (e.g., hydrocortisone) to rule out adrenal insufficiency
- Drug interactions and precautions (including self-management)
- Medications/substances that cause reduced absorption: calcium preparations, iron supplements, antacids (containing aluminum), sucralfate, cholestyramine, etc. should be taken at least 4 hours apart from levothyroxine
- Others: anticonvulsants (rifampicin, phenobarbital, etc.) and enzyme inducers increase levothyroxine metabolism → a dose increase may be necessary
- Anticoagulants such as warfarin: thyroid hormones may enhance the anticoagulant effect, so INR monitoring is necessary
- How to take it: take on an empty stomach (30–60 minutes before breakfast) or 3 hours after bedtime is recommended (maintain consistency)
- Dose reassessment is necessary during pregnancy, weight changes, breastfeeding, surgery, or when starting or stopping certain medications
- Precautions for complications and long-term management
- Inappropriate overdosing: palpitations and increased risk of osteoporosis (especially with long-term high doses)
- Untreated or delayed treatment: hyperlipidemia, worsening cardiovascular disease, and, in severe cases, myxedema coma
- Most primary Hashimoto’s cases are generally permanent, so long-term medication and follow-up are necessary
Outpatient Visit Checklist (Preparation and Example Questions)
- Items/information to bring
- List of currently used medications and supplements (including the exact formulation and time of administration; calcium, iron, and antacids are especially important)
- Previous test results (recent TSH, free T4, anti-TPO/Tg antibodies, and, if necessary, thyroid ultrasound and biopsy results)
- History of surgery, radioactive iodine treatment, or radiation to the neck
- History of cardiovascular disease (angina, myocardial infarction, arrhythmia, etc.)
- Whether you are pregnant, planning a pregnancy, or breastfeeding
- Records of symptom changes (onset, patterns of worsening and improvement), weight changes, and menstrual changes
- Information to tell the healthcare provider in advance during the outpatient visit
- Medications recently started or stopped (especially iron, calcium, anticonvulsants, antituberculosis drugs, etc.)
- History of allergies or adverse effects
- Whether you have heart disease or are an older adult
Examples of General Questions to Ask the Doctor
- What are the expected side effects of this medication (levothyroxine)? What symptoms should I watch for?
- What is the target range for TSH (or free T4) in my case? How often should I be tested?
- How should I schedule the dosing time (morning on an empty stomach vs. bedtime)? Can I take it together with my other medications?
- I am planning a pregnancy. How should my dose be adjusted?
- How will osteoporosis or effects on the heart be monitored during long-term treatment?
Examples of Disease-Specific Questions
- In my case (for example, depending on anti-TPO positivity, age, and whether I have heart disease), is this hypothyroidism permanent? Do I need to take medication for life?
- I am taking calcium/iron supplements (or vitamins and antacids). How far apart should I take them from levothyroxine?