Iatrogenic hyperthyroidism secondary to dextrothyroxine administration

Two patients are reported who presented with clinical hyperthyroidism, increased serum thyroid function studies, and depressed radioactive iodine uptake, secondary to chronic ingestion of D-T4. Symptoms abated, and function studies returned to normal, following discontinuation of D-T4. This uncommon effect of D-T4 may be more prevalent than is generally realized and must be recognized as another potential cause of low radioiodine uptake in patients with clinical hyperthyroidism.