Radioactive iodine is most successful in treating hyperthyroidism that results from which condition?

• A. Grave's disease.
• B. Subacute thyroiditis.
• C. Hashimoto's thyroiditis.
• D. Papillary thyroid carcinoma.

Answer: (A)

Radioactive iodine therapy works best when the thyroid is actively taking up iodine and producing excess hormone. Graves’ disease causes diffuse, iodine-avid stimulation of the entire thyroid due to autoimmune TSH receptor activation, so radioactive iodine selectively destroys overactive tissue and lowers thyroid hormone production.

In subacute thyroiditis, the thyroxin excess comes from leakage of preformed hormone, not increased synthesis, and uptake of iodine is low, so radioactive iodine isn’t effective. Hashimoto’s thyroiditis can have a transient hyperthyroid phase, but the underlying problem is autoimmune destruction leading to hypothyroidism, with variable uptake that isn’t ideal for this therapy. Papillary thyroid carcinoma isn’t treated for hyperthyroidism itself; radioactive iodine is used to ablate residual cancer tissue after surgery, not to manage hormone excess.