Endocrinology: hypocalcaemic tetany: 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 · Endocrinology: hypocalcaemic tetany

Sample item

After total thyroidectomy a woman develops perioral tingling. Inflating a blood pressure cuff on her arm above systolic pressure for three minutes produces carpal spasm. What is the mechanism?

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

The answer and the reasoning

C. Low ionised calcium lowers the threshold for sodium channel opening, increasing nerve excitability

Low extracellular calcium reduces the surface charge screening, so sodium channels open at a less depolarised potential and nerves fire spontaneously. This produces Chvostek and Trousseau signs after parathyroid damage.

Option by option

  • A. Low magnesium blocking calcium channels

    Magnesium is not the primary issue after thyroidectomy.

  • B. Raised calcium blocks sodium channels

    Hypercalcaemia reduces excitability, which gives weakness.

  • C. Low ionised calcium lowers the threshold for sodium channel opening, increasing nerve excitability (correct)

    Correct. Hypocalcaemia lowers threshold and causes hyperexcitability.

  • D. Hyperkalaemia depolarising the membrane

    Hyperkalaemia is not the issue in this setting.

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 C, Low ionised calcium lowers the threshold for sodium channel opening, increasing nerve excitability. Low extracellular calcium reduces the surface charge screening, so sodium channels open at a less depolarised potential and nerves fire spontaneously.

Why is "Low magnesium blocking calcium channels" not the answer?

Magnesium is not the primary issue after thyroidectomy.

Why is "Raised calcium blocks sodium channels" not the answer?

Hypercalcaemia reduces excitability, which gives weakness.

Why is "Hyperkalaemia depolarising the membrane" not the answer?

Hyperkalaemia is not the issue in this setting.

What concept does this question test?

It tests Endocrinology: hypocalcaemic tetany in Physiology. This produces Chvostek and Trousseau signs after parathyroid damage.

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: hypocalcaemic tetany?

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.