Effect of Methimazole Therapy on Thyroid Pathohistology That May Mimic Thyroid Malignancy.

Diffuse toxic goiter, as the most common cause of hyperthyroidism, is usually initially treated with thyrostatic drugs such as methimazole, followed by radioiodine therapy or surgery which may be indicated as definitive treatment. Radioactive iodine therapy has a known association with various histopathologic features including cytologic atypia, but herein we present a rare example of morphological thyrocyte changes induced by long-term pharmacological treatment with methimazole that mimicked thyroid malignancy in a pathohistological sample.