Endocrinology: inferior petrosal sinus sampling: 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: inferior petrosal sinus sampling

Sample item

A patient has ACTH-dependent Cushing syndrome with a 4 mm pituitary lesion on MRI and failure of suppression on high-dose dexamethasone is equivocal. What investigation separates pituitary from ectopic ACTH source?

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

The answer and the reasoning

A. Inferior petrosal sinus sampling with a central to peripheral ACTH ratio above 2 at baseline or 3 after CRH

Bilateral inferior petrosal sinus sampling compares ACTH in the sinuses with peripheral blood. A central to peripheral gradient of 2 or more at baseline, or 3 or more after CRH, indicates a pituitary source. It is used when imaging and dynamic tests are discordant or the lesion is small.

Option by option

  • A. Inferior petrosal sinus sampling with a central to peripheral ACTH ratio above 2 at baseline or 3 after CRH (correct)

    Correct. IPSS localises ACTH secretion.

  • B. Urinary catecholamines

    Catecholamines assess phaeochromocytoma.

  • C. Repeat random cortisol

    Random cortisol does not localise the source.

  • D. CT adrenal

    Adrenal CT is for ACTH-independent disease.

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 A, Inferior petrosal sinus sampling with a central to peripheral ACTH ratio above 2 at baseline or 3 after CRH. Bilateral inferior petrosal sinus sampling compares ACTH in the sinuses with peripheral blood.

Why is "Urinary catecholamines" not the answer?

Catecholamines assess phaeochromocytoma.

Why is "Repeat random cortisol" not the answer?

Random cortisol does not localise the source.

Why is "CT adrenal" not the answer?

Adrenal CT is for ACTH-independent disease.

What concept does this question test?

It tests Endocrinology: inferior petrosal sinus sampling in General Medicine. A central to peripheral gradient of 2 or more at baseline, or 3 or more after CRH, indicates a pituitary source. It is used when imaging and dynamic tests are discordant or the lesion is small.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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: inferior petrosal sinus sampling?

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.