Thyroid Disorders USMLE Step 1 Practice Question
A 67-year-old woman presents to clinic with a 3-month history of fatigue, weight gain, constipation, and cold intolerance. Her past medical history is significant for atrial fibrillation managed with warfarin and metoprolol. She reports no new medications, but mentions she started taking iodine-rich kelp supplements approximately 4 months ago for joint pain after reading about their health benefits online. Vital signs show heart rate 52 bpm, and laboratory studies reveal: TSH: 18 mIU/L (normal 0.5–5.0)
Free T4: 0.6 ng/dL (normal 0.8–1.8)
TPO antibodies: negative
Thyroglobulin antibodies: negative Which of the following best explains this patient's thyroid dysfunction?
Answer choices
- AWolff-Chaikoff effect from excessive iodine intakeCorrect answer
- BWarfarin-induced inhibition of thyroid peroxidase
- CMetoprolol-related suppression of TSH secretion
- DAtrial fibrillation with resultant thyroid hormone consumption
- EAcute autoimmune thyroiditis triggered by iodine supplementation
- FAge-related primary hypothyroidism coincidentally diagnosed
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