Underactive thyroid (hypothyroidism)
Also known as: hypothyroidism, Hashimoto's thyroiditis, myxoedema
Insufficient thyroid hormone, most often because the immune system destroys the thyroid gland, slowing the body's metabolism.
Overview
Thyroxine sets the pace of nearly every cell, so its lack slows everything: energy, thought, bowel, heart rate and heat production. Symptoms creep in over months and are easily mistaken for ageing or depression. A simple blood test makes the diagnosis and a daily tablet of levothyroxine restores normal life.
Causes
- Autoimmune (Hashimoto's) thyroiditis
- Treatment of an overactive thyroid (radioiodine, surgery)
- Iodine deficiency worldwide
- Drugs: amiodarone, lithium, immunotherapy
- Pituitary failure (rare)
- Congenital
Risk factors
- Female sex
- Age over 60
- Family history
- Other autoimmune disease
- Pregnancy and the year after
Symptoms
What a clinician may find
- Weight gain, dry skin and hair, puffy face
- Slow pulse, cold intolerance
- Slow-relaxing reflexes
- Goitre
- Hoarse voice, constipation, heavy periods
Complications
- High cholesterol and heart disease
- Depression and cognitive slowing
- Infertility and pregnancy complications
- Myxoedema coma (rare, life-threatening)
Diagnosis
A raised TSH with a low free T4 confirms primary hypothyroidism; thyroid peroxidase antibodies indicate the autoimmune cause. Cholesterol is often raised.
Treatment
Levothyroxine once daily on an empty stomach, dose adjusted by TSH every six to eight weeks until stable, then checked yearly; higher doses are needed in pregnancy.
Prevention
Adequate iodine intake; screening in pregnancy and after thyroid treatment.
When to seek care
See a doctor for persistent tiredness with weight gain, cold intolerance or low mood; emergency care for drowsiness, very low temperature or confusion in someone with known hypothyroidism.