Radiotherapy and nuclear medicine basics: MIBG interfering drugs: practice question

A Radiology 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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Radiology · Radiotherapy and nuclear medicine basics: MIBG interfering drugs

Sample item

A patient on labetalol and a tricyclic antidepressant is booked for an MIBG scan for suspected phaeochromocytoma. What is the correct approach?

AWithhold the interfering drugs before the scanBGive a loading dose of the same drugs on the scan dayCContinue them because they raise tumour uptakeDDouble the MIBG dose to compensate

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

The answer and the reasoning

A. Withhold the interfering drugs before the scan

Labetalol, tricyclic antidepressants and some sympathomimetics block uptake of MIBG into chromaffin cells and cause false negatives. They should be stopped for a suitable period before the scan if clinically safe, and thyroid blockade is also used.

Option by option

A. Withhold the interfering drugs before the scan (correct)
Correct. These drugs inhibit MIBG uptake, so they are withheld beforehand to avoid false-negative results.
B. Give a loading dose of the same drugs on the scan day
Additional drug on the day would further reduce uptake.
C. Continue them because they raise tumour uptake
These drugs reduce tumour uptake rather than raise it.
D. Double the MIBG dose to compensate
Doubling the dose raises radiation exposure and does not reliably overcome the blockade.

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.

Questions about this Radiology question

What is the answer to this Radiology question?

The best answer is A, Withhold the interfering drugs before the scan. Labetalol, tricyclic antidepressants and some sympathomimetics block uptake of MIBG into chromaffin cells and cause false negatives.

Why is "Give a loading dose of the same drugs on the scan day" not the answer?

Additional drug on the day would further reduce uptake.

Why is "Continue them because they raise tumour uptake" not the answer?

These drugs reduce tumour uptake rather than raise it.

Why is "Double the MIBG dose to compensate" not the answer?

Doubling the dose raises radiation exposure and does not reliably overcome the blockade.

What concept does this question test?

It tests Radiotherapy and nuclear medicine basics: MIBG interfering drugs in Radiology. They should be stopped for a suitable period before the scan if clinically safe, and thyroid blockade is also used.

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 Radiotherapy and nuclear medicine basics: MIBG interfering drugs?

Learn signs with the image, and the disease they point to. Then use the flashcards and the other Radiology 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.