- Hashimoto’s thyroiditis
- Iodine deficiency (rare in developed world)
- Thyroid surgery, irradiation, or radioiodine
- Subacute (de Quervain’s) thyroiditis (after initial hyperthyroidism)
- Severe illness
- Drugs causing hypothyroidism: lithium, amiodarone, propylthiouracil, methimazole, phenylbutazone, sulfonamides, interferon ?
- Riedel’s thyroiditis
- Deficient pituitary thyroid-stimulating hormone (TSH)
- "Subclinical" hypothyroidism: high TSH, clinically euthyroid, normal T4
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