In some people with long-term Hashimoto’s thyroiditis who later develop hyperthyroidism, antibodies that activate the TSH receptor can be found, suggesting a change in the type of immune response directed at this receptor.

In some people with Hashimoto’s thyroiditis who later develop hyperthyroidism, thyroid-stimulating receptor antibodies can be found in the blood, but their presence alone does not prove they cause the shift to hyperthyroidism, because other biological processes like thyroid damage or changes in immune activity may also be involved.

In Graves’ disease, the immune system makes faulty antibodies that trick the thyroid into overproducing hormones, causing it to go into overdrive.

A woman with Hashimoto’s thyroiditis, who had been stable on thyroid hormone replacement for ten years, developed hyperthyroidism alongside a change in her autoimmune antibodies from those targeting the thyroid peroxidase to those targeting the thyroid-stimulating hormone receptor.

In Graves’ disease, certain antibodies in the body mistakenly turn on the thyroid gland and can also affect the eyes, causing swelling and bulging — it's like the immune system accidentally hits the gas pedal on both the thyroid and eye tissues.