Thyroid Disorders USMLE Step 1 Practice Question
A 54-year-old man presents to clinic with progressive fatigue, weight gain, and decreased libido over the past 6 months. He has a history of Hodgkin lymphoma treated with mediastinal radiation 20 years ago. On examination, he appears lethargic with dry skin and bradycardia (HR 52 bpm). Laboratory studies reveal: TSH 1.8 mIU/L (normal 0.4-4.0), free T4 0.6 ng/dL (normal 0.7-1.9), ACTH 18 pg/mL (normal 7-46), and morning cortisol 6 mcg/dL (normal 8-20). Which of the following is the most likely diagnosis?
Answer choices
- APrimary hypothyroidism from radiation-induced destruction of thyroid follicles
- BAutoimmune thyroiditis triggered by radiation exposure to thyroid tissue
- CCentral hypothyroidism due to pituitary dysfunction from radiation exposureCorrect answer
- DSecondary adrenal insufficiency with resultant hypothyroid symptoms
- EThyroid hormone resistance syndrome from post-radiation genetic mutation
- FFactitious hyperthyroidism with suppressed TSH from levothyroxine overuse
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