Q. A 72-year-old woman presents to her primary care physician with a complaint of enlargement of her thyroid gland. She reports that the enlargement has been gradually increasing over the past few years and is now quite noticeable. She has no other significant medical history. The patient lives in an area known for iodine deficiency. On physical examination, the patient is found to have a large, painless goiter. Thyroid function tests show an elevated T3 level and a decreased TSH level. A thyroid scintigraphy shows increased radioiodine uptake by multiple hyperfunctioning areas and decreased uptake by the rest of the gland and intervening parenchyma. What is the most likely diagnosis for this patient?