Endocrinology and diabetes: acute iodide effect on thyroid hormone release: practice question

A General Medicine question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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General Medicine · Endocrinology and diabetes: acute iodide effect on thyroid hormone release

Sample item

A patient with Graves disease is given a large dose of iodide before thyroid surgery and thyroid hormone release falls promptly. Which mechanism explains this?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

D. Excess iodide transiently inhibits hormone organification

A large iodide load transiently inhibits iodide organification and hormone release, known as the Wolff-Chaikoff effect. It also reduces gland vascularity, which is why it is given before surgery. The effect wears off in some patients as the gland escapes.

Option by option

  • A. Competitive blockade of the iodide transporter by perchlorate

    Perchlorate blocks iodide uptake and is a different mechanism and drug.

  • B. Destruction of follicular cells by radiation

    Gland destruction is the effect of radioiodine, which acts over weeks.

  • C. Blocked peripheral conversion of T4 to T3

    Reduced T4 to T3 conversion is the action of propranolol and propylthiouracil, not iodide.

  • D. Excess iodide transiently inhibits hormone organification (correct)

    Correct. High iodide briefly suppresses organification and release of hormone.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this General Medicine question

What is the answer to this General Medicine question?

The best answer is D, Excess iodide transiently inhibits hormone organification. A large iodide load transiently inhibits iodide organification and hormone release, known as the Wolff-Chaikoff effect.

Why is "Competitive blockade of the iodide transporter by perchlorate" not the answer?

Perchlorate blocks iodide uptake and is a different mechanism and drug.

Why is "Destruction of follicular cells by radiation" not the answer?

Gland destruction is the effect of radioiodine, which acts over weeks.

Why is "Blocked peripheral conversion of T4 to T3" not the answer?

Reduced T4 to T3 conversion is the action of propranolol and propylthiouracil, not iodide.

What concept does this question test?

It tests Endocrinology and diabetes: acute iodide effect on thyroid hormone release in General Medicine. It also reduces gland vascularity, which is why it is given before surgery. The effect wears off in some patients as the gland escapes.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Endocrinology and diabetes: acute iodide effect on thyroid hormone release?

For each disease know the classic presentation, the best test, and the first-line treatment. Then use the flashcards and the other General Medicine questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.