A 41-year-old woman presents with a 3-month history of fatigue, constipation, weight gain, and cold intolerance. Vital signs show HR 52 bpm, BP 128/82 mmHg, temperature 36.2°C. Physical examination reveals dry skin, delayed relaxation of Achilles reflex, and no thyroid nodules. Laboratory studies demonstrate TSH 8.5 mIU/L (normal 0.4-4.0) and free T4 0.8 ng/dL (normal 0.8-1.8). She denies recent iodine supplement use. Which of the following is the most likely diagnosis?

1. A)Hyperthyroidism due to Graves disease
2. B)Euthyroid sick syndrome
3. C)Secondary hypothyroidism
4. D)Primary hypothyroidismGABARITO
5. E)Subacute granulomatous thyroiditis