A 31-year-old woman presents with fever 40°C, delirium, tachycardia 150/min, and a diffusely enlarged tender-free goitre following an upper respiratory infection. Free T4 is markedly elevated. Which component of therapy specifically reduces peripheral conversion of T4 to T3?
- A Propylthiouracil ✓
- B Propranolol
- C Lugol iodine given before the thionamide
- D Hydrocortisone
Correct answer: A. Propylthiouracil
Explanation
Propylthiouracil uniquely inhibits peripheral deiodination of T4 to T3 in addition to blocking hormone synthesis, which is why it is preferred over methimazole in thyroid storm. Propranolol controls adrenergic symptoms and also mildly blocks conversion but the thionamide effect is the classic answer. Iodine must follow the thionamide by at least an hour to prevent substrate-driven hormone synthesis.
Reference: Williams Textbook of Endocrinology, 14th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.