The two main forms of autoimmune thyroid disease are Hashimoto’s thyroiditis and Graves’ disease. Hashimoto’s thyroiditis is a chronic inflammation of the thyroid gland that typically, but not necessarily, causes hypothyroidism. While Graves’ disease is a different form of immune system attack on the thyroid that often causes hyperthyroidism. While Hashimoto’s thyroiditis is much more common than Graves’ disease, which explains why hypothyroidism is much more common than hyperthyroidism, the two conditions may have similar genetic predispositions, and can both occur in different members of the same family.
In many patients, however, the two conditions may coexist with one being more dominant than the other. This is the reason why many patients treated for Graves’ disease and hyperthyroidism can, over time, not only enter in remission, but can also become hypothyroid as a result of Hashimoto’s thyroiditis becoming the most dominant disorder. This is as if Hashimoto’s thyroiditis follows Graves’ disease.
There are also many patients who suffer from Hashimoto’s thyroiditis and even hypothyroidism caused by the Hashimoto’s thyroiditis who, all of a sudden, switch to become Graves’ disease patients which requires stopping the thyroid medication that they were receiving, as well as treating the hyperthyroidism.
The reason why the immune system changes the way it is attacking the thyroid gland can be anything going from stress, smoking, changes in iodine intake, pregnancy, radiation, or other environmental factors. The change in the immune system activity directed at the thyroid gland going from straight forward inflammation to stimulation of the gland, can happen anytime in the course of the treatment of Hashimoto’s thyroiditis.
If you have Hashimoto’s thyroiditis and hypothyroidism and are treated with thyroid medications, do not assume that your thyroid function tests will remain stable the rest of your life with thyroid treatment. This is why you will need routine and regular monitoring of your thyroid tests. The occurrence of high thyroid hormone levels while being treated may suggest to your doctor that your thyroid gland could be shifting from Hashimoto’s thyroiditis to Graves’ disease.