Intravenous and inhalational agents: myotonic dystrophy and suxamethonium: practice question

A Anaesthesia 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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Anaesthesia · Intravenous and inhalational agents: myotonic dystrophy and suxamethonium

Sample item

A 32-year-old man with myotonic dystrophy and a cardiac conduction defect needs general anaesthesia. Why is suxamethonium best avoided?

AIt causes life-threatening hyperkalaemia in all patients with a myopathyBIt is cleared slowly because plasma cholinesterase is usually absentCIt can provoke a sustained generalised myotonic contracture that makes ventilation and intubation difficultDIt triggers malignant hyperthermia in every patient with myotonia

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

The answer and the reasoning

C. It can provoke a sustained generalised myotonic contracture that makes ventilation and intubation difficult

Depolarisation in myotonic muscle can cause prolonged contracture that is not reliably relieved by non-depolarising agents, and it may impair ventilation. Short-acting non-depolarisers with sugammadex reversal are preferred, with attention to the cardiac conduction defect and sensitivity to sedatives.

Option by option

A. It causes life-threatening hyperkalaemia in all patients with a myopathy
Hyperkalaemia is a concern in denervation and muscular dystrophies such as Duchenne, not the principal issue here.
B. It is cleared slowly because plasma cholinesterase is usually absent
Cholinesterase activity is not characteristically absent in myotonic dystrophy.
C. It can provoke a sustained generalised myotonic contracture that makes ventilation and intubation difficult (correct)
Correct. Myotonic contracture after suxamethonium is the specific hazard.
D. It triggers malignant hyperthermia in every patient with myotonia
Myotonia is not an established trigger state for malignant hyperthermia in every patient.

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 Anaesthesia question

What is the answer to this Anaesthesia question?

The best answer is C, It can provoke a sustained generalised myotonic contracture that makes ventilation and intubation difficult. Depolarisation in myotonic muscle can cause prolonged contracture that is not reliably relieved by non-depolarising agents, and it may impair ventilation.

Why is "It causes life-threatening hyperkalaemia in all patients with a myopa…" not the answer?

Hyperkalaemia is a concern in denervation and muscular dystrophies such as Duchenne, not the principal issue here.

Why is "It is cleared slowly because plasma cholinesterase is usually absent" not the answer?

Cholinesterase activity is not characteristically absent in myotonic dystrophy.

Why is "It triggers malignant hyperthermia in every patient with myotonia" not the answer?

Myotonia is not an established trigger state for malignant hyperthermia in every patient.

What concept does this question test?

It tests Intravenous and inhalational agents: myotonic dystrophy and suxamethonium in Anaesthesia. Short-acting non-depolarisers with sugammadex reversal are preferred, with attention to the cardiac conduction defect and sensitivity to sedatives.

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 Intravenous and inhalational agents: myotonic dystrophy and suxamethonium?

Make a table of each agent, its key advantage and its main side effect. Then use the flashcards and the other Anaesthesia 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.