A 24-year-old man comes to the physician for a 1-month history of sensation of fullness in his neck. Physical examination shows a nodule. TSH is 2.0 mIU/L. Ultrasound is performed followed by fine-needle aspiration. The specimen shows apple-green birefringence with Congo red stain. Which of the following is the most appropriate next best step in management?
Check serum calcium
Check serum metanephrines
131Iodine uptake scan
Core-needle biopsy
Thyroidectomy
