Adrenal: dexamethasone suppression: practice question

A Physiology 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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Physiology · Adrenal: dexamethasone suppression

Sample item

A 34-year-old woman with Cushingoid features has raised ACTH. Her cortisol does not suppress with 1 mg low-dose dexamethasone but falls by more than 50% with high-dose dexamethasone. What is the most likely source of excess ACTH?

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

The answer and the reasoning

A. Pituitary corticotroph adenoma

A pituitary corticotroph adenoma keeps some responsiveness to glucocorticoid feedback, which is overcome at low dose but achieved at high dose. An ectopic ACTH source such as small cell carcinoma does not respond to feedback and shows no suppression. Adrenal tumours and exogenous steroids cause low ACTH because of suppression of the pituitary.

Option by option

  • A. Pituitary corticotroph adenoma (correct)

    Correct. Partial feedback sensitivity gives suppression at high dose in Cushing disease.

  • B. Exogenous glucocorticoid therapy

    Exogenous steroids would suppress ACTH, not raise it.

  • C. Adrenocortical adenoma

    An adrenal adenoma would produce a low ACTH and no suppression.

  • D. Small cell carcinoma of the lung

    Ectopic ACTH secretion is autonomous and does not suppress at either dose.

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 Physiology question

What is the answer to this Physiology question?

The best answer is A, Pituitary corticotroph adenoma. A pituitary corticotroph adenoma keeps some responsiveness to glucocorticoid feedback, which is overcome at low dose but achieved at high dose.

Why is "Exogenous glucocorticoid therapy" not the answer?

Exogenous steroids would suppress ACTH, not raise it.

Why is "Adrenocortical adenoma" not the answer?

An adrenal adenoma would produce a low ACTH and no suppression.

Why is "Small cell carcinoma of the lung" not the answer?

Ectopic ACTH secretion is autonomous and does not suppress at either dose.

What concept does this question test?

It tests Adrenal: dexamethasone suppression in Physiology. An ectopic ACTH source such as small cell carcinoma does not respond to feedback and shows no suppression. Adrenal tumours and exogenous steroids cause low ACTH because of suppression of the pituitary.

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 Adrenal: dexamethasone suppression?

For each system, sketch the key graph (pressure–volume loop, oxygen dissociation curve, nephron handling) and explain it aloud. Then use the flashcards and the other Physiology 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.