Endocrinology
Hypothyroidism
갑상선저하증
Thyroid hormone deficiency causing systemic metabolic slowdown
- How common
- 5% women, 1% men
- Typical age
- Increases age ≥40
What is it?
Most cases autoimmune (Hashimoto); reduced T4/T3 secretion with compensatory TSH rise.
Commonly affected: Thyroid → systemic metabolism
How it develops
- Gland injuryAutoimmune (Hashimoto), surgery, radiation
- Low T4/T3Decreased synthesis/secretion
- Loss of negative feedbackCompensatory TSH rise (>4.5 mIU/L)
- Metabolic slowdownReduced HR, temp, GI motility, nerves
Symptoms
- Fatigue/lethargyMetabolic slowdown
- Cold intoleranceImpaired thermoregulation
- Weight gainDespite stable appetite
- Constipation/bradycardiaSlow GI/heart
- Dry skin/hair lossCoarse skin, lateral eyebrow loss
How it is examined
- TSH (screening)TSH >4.5 mIU/L → primary
- Free T4Low free T4 → overt hypothyroidism
- Anti-TPO antibodyHashimoto diagnosis
Imaging
No imaging needed for diagnosis.
- Clinical + lab
Thyroid US for suspected nodule.
- Heterogeneous gland
Non-surgical care
- Levothyroxine1.6 μg/kg/day, take fasting
- Dose titration (TSH monitor)Recheck TSH q4–6 wks
- Timing education30–60 min before meal; separate from Ca/Fe
- Low start in elderly/cardiacElderly: start 25 μg
Conservative options are generally tried first. Medications listed here can have side effects — discuss them with your prescriber.
When surgery is considered
None (hormone replacement)
Outlook
Lifelong levothyroxine restores normal life.