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 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 some people with Hashimoto thyroiditis, antibody levels may drop to undetectable levels without surgery, and this change may occur alongside improvement in ongoing hypothyroid symptoms even after taking levothyroxine.

In people with subclinical hypothyroidism, higher levels of anti-thyroid peroxidase antibodies are linked to more frequent levothyroxine prescription and more irregular appearance of the thyroid gland on ultrasound.

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 people with Hashimoto thyroiditis, levels of thyroid peroxidase antibodies usually remain elevated. A return to normal levels is uncommon and typically happens only after medical treatments like selenium supplements, thyroid hormone medication, or surgical removal of the thyroid.