Hashimoto's thyroiditis

Hashimoto’s thyroiditis is the immune system slowly dismantling the thyroid factory. Over years, the body’s own white cells infiltrate and destroy the gland, so output gradually dwindles until it can no longer keep up.

It is an autoimmune disease in which immune cells and antibodies — typically against thyroid peroxidase — attack and replace thyroid tissue with scar and immune infiltrate. Early on the gland may be normal or even briefly leak hormone; over time it fails, making Hashimoto’s the most common cause of hypothyroidism in iodine-sufficient regions. The thyroid may feel firm and rubbery, sometimes enlarged into a goiter, sometimes shrunken.

Diagnosis combines a high TSH with low thyroid hormone and positive anti-thyroid antibodies. There is no way to stop the underlying autoimmunity, so treatment simply replaces what the gland can no longer make, using daily levothyroxine titrated to normalize TSH. Hashimoto’s often keeps company with other autoimmune conditions, such as type 1 diabetes or vitiligo, in the same person or family.