Which condition shows decreased radioactive iodine uptake (RAIU) compared with other hyperthyroid conditions?

• A. Subacute thyroiditis
• B. Graves' disease
• C. Toxic multinodular goiter
• D. Normal thyroid function

Answer: (A)

Radioactive iodine uptake reflects how actively the thyroid is trapping iodine for hormone production. In thyrotoxicosis caused by increased hormone synthesis, such as Graves’ disease, the gland is hyperactive and shows high uptake. In toxic multinodular goiter, autonomous nodules produce hormone, so uptake is increased in the hyperfunctioning areas. In subacute thyroiditis, however, the thyrotoxicosis comes from rupture of thyroid follicles and release of preformed hormone rather than new hormone synthesis; the damaged gland traps iodine poorly, so the uptake is decreased. Normal thyroid function would typically show normal uptake, not a decrease like seen in destructive thyroiditis.