Review Question - QID 108726

A 32-year-old G1P0 woman at 12 weeks gestation presents to her obstetrician for a follow-up appointment. She first presented 4 weeks ago with bilateral hand tremors. At that time, she was found to have a thyroid-stimulating hormone (TSH) concentration <0.01 mU/L and an elevated free T4. She was started on propranolol and propylthiouracil. The dosage of both medications has been titrated to the maximum dose. She reports mild improvement in her symptoms but continues to experience sweating and palpitations. She has a past medical history of polycystic ovary syndrome. Her family history is notable for hypothyroidism in her mother. She does not smoke cigarettes, stopped drinking alcohol prior to pregnancy, and does not use drugs. Her temperature is 97.6°F (36.4°C), blood pressure is 113/70 mmHg, pulse is 126/min, and respirations are 18/min. On physical exam, she appears anxious, mildly diaphoretic and has a non-tender prominence on her neck which is shown in Figure A. Which of the following is the most appropriate next step in management?