Hashimoto's Thyroiditis
Hashimoto's thyroiditis is the autoimmune destruction of the thyroid gland and the leading cause of hypothyroidism in the U.S., causing up to 85% of cases, per ATA Guidelines for the Treatment of Hypothyroidism.
Symptoms
Fatigue, weight gain, cold intolerance, dry skin, hair thinning, and constipation -- the same symptoms as hypothyroidism generally, since Hashimoto's is the cause in most cases.
Causes and risk
An autoimmune process where the body's own antibodies attack the thyroid; family history of autoimmune disease and being female both raise risk substantially.
How it is evaluated
TSH confirms hypothyroidism; thyroid peroxidase (TPO) antibodies confirm the autoimmune (Hashimoto's) cause specifically, though a positive antibody alone without abnormal TSH doesn't require treatment.
Treatment
Levothyroxine is first-line once TSH is elevated, dosed around 1.6 mcg/kg/day with rechecks at 6-8 weeks after any change. Subclinical hypothyroidism (mildly elevated TSH, normal free T4) is treated selectively -- generally for TSH of 10 mIU/L or higher, positive antibodies, or symptoms -- rather than automatically. Combination T3/T4 or desiccated thyroid is not routinely recommended per the ATA guideline.
When to seek care
Myxedema coma -- hypothermia, altered mental status, slowed breathing -- is a rare emergency. A significantly enlarged thyroid causing difficulty breathing or swallowing also needs prompt evaluation.