Respiratory medicine: paraneoplastic SIADH: 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 · Respiratory medicine: paraneoplastic SIADH

Sample item

A 62-year-old smoker has a central hilar mass. His serum sodium is 120 mmol/L, urine osmolality is 450 mOsm/kg and he is clinically euvolaemic. Which tumour type is most likely?

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

The answer and the reasoning

B. Small cell carcinoma

Small cell lung cancer is a neuroendocrine tumour that produces ectopic ADH and causes SIADH, as well as ectopic ACTH. Squamous carcinoma instead produces PTHrP and hypercalcaemia. Small cell tumours are centrally placed and spread early.

Option by option

  • A. Adenocarcinoma

    Adenocarcinoma is usually peripheral and associated with hypertrophic osteoarthropathy.

  • B. Small cell carcinoma (correct)

    Correct. Small cell carcinoma is the classic cause of ectopic ADH secretion.

  • C. Squamous cell carcinoma

    Squamous carcinoma is central but characteristically causes hypercalcaemia through PTHrP.

  • D. Large cell carcinoma

    Large cell carcinoma is peripheral and is not typically linked with SIADH.

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 B, Small cell carcinoma. Small cell lung cancer is a neuroendocrine tumour that produces ectopic ADH and causes SIADH, as well as ectopic ACTH.

Why is "Adenocarcinoma" not the answer?

Adenocarcinoma is usually peripheral and associated with hypertrophic osteoarthropathy.

Why is "Squamous cell carcinoma" not the answer?

Squamous carcinoma is central but characteristically causes hypercalcaemia through PTHrP.

Why is "Large cell carcinoma" not the answer?

Large cell carcinoma is peripheral and is not typically linked with SIADH.

What concept does this question test?

It tests Respiratory medicine: paraneoplastic SIADH in General Medicine. Squamous carcinoma instead produces PTHrP and hypercalcaemia. Small cell tumours are centrally placed and spread early.

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 Respiratory medicine: paraneoplastic SIADH?

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.