Audio Qbank – Q331 – A 39F with neck swelling

A 39-year-old woman comes to the physician for a 2-month history of fatigue and neck swelling. She reports no weight change or cold intolerance. Her menstrual cycle the past year has fluctuated between 28 and 33 days in length. Serum cholesterol and hepatic AST are elevated. Serum TSH, T3, and T4 are all within normal range. Antibody screening shows positive titers against thyroperoxidase and thyroglobulin. Physical examination shows a diffusely enlarged thyroid gland without nodularity. Which of the following is the most likely diagnosis?