“The two main disorders that comprise autoimmune thyroid disease are Hashimoto thyroiditis and Graves disease. The former is the most common cause of hypothyroidism, whereas the latter is a major cause of hyperthyroidism. Occasionally, a patient may present with features of one of these disorders at one time and features of the other at another time. The usual sequence is hyperthyroidism followed by hypothyroidism. However, cases of hypothyroidism followed by hyperthyroidism, such as in our patient, have also been described.”
- Rarely, autoimmune hyperthyroidism can occur after many years of hypothyroidism in patients with Hashimoto thyroiditis.
- When a patient on L-T4 for Hashimoto hypothyroidism presents with hyperthyroidism, over-replacement with L-T4 is the likely cause, but the possibility of endogenous hyperthyroidism should also be considered.
- Although radioactive iodine therapy for Graves disease is generally safe, especially in an otherwise healthy patient, severe exacerbations of hyperthyroidism can occur, and close monitoring in the first few weeks after therapy is prudent.