A 50-year-old man comes to the office with a 2-day history of malaise, fever, fatigue and pain in front of his neck. He recovered from an upper respiratory illness a week prior but he previously had felt well. His medical history is unremarkable. Temperature is 38.5C, blood pressure is 150/70 mmHg, and pulse is 110 bpm. The thyroid gland is diffusely enlarged and tender. Laboratory results are as follows: Hemoglobin: 13.9 g/dL (normal 13.5 - 17.5 g/dL) Hematocrit: 44% (normal 36% - 46%) Platelets: 200,000/mm3 (normal 150,000 - 400,000/mm3) Leukocytes: 10,500/mm3 (normal 4,500 - 11,000/mm3) TSH <0.001 uU/mL (normal 0.4 - 4.0 ng/dL) Free (T4) 4.6 ng/dL (normal 0.9 - 2.4 ng/dL) ESR 100 mm/hr (normal 0 - 15 mm/h) Which of the following is the most likely diagnosis in this patient?