Question:medium
A 25 year old woman presents with generalized restriction of eye movement in all directions, intermittent ptosis, proximal muscle weakness, and fatigability. Which is the MOST useful test in making the diagnosis?
A 25 year old woman presents with generalized restriction of eye movement in all directions, intermittent ptosis, proximal muscle weakness, and fatigability. Which is the MOST useful test in making the diagnosis?
Show Hint
A rapid-acting anticholinesterase that briefly reverses the ptosis points to the diagnosis.
Updated On: Jun 24, 2026
- CPK
- Edrophonium test
- EMG
- Muscle biopsy
Show Solution
The Correct Option is B
Solution and Explanation
Step 1: A young woman with drooping eyelids that come and go, eye movements limited in every direction, and limb weakness that grows with exertion fits myasthenia gravis, an antibody-mediated failure of signal transmission at the neuromuscular junction.
Step 2: To confirm it quickly, the edrophonium challenge is preferred. By briefly blocking acetylcholinesterase, edrophonium boosts available acetylcholine, and an immediate but short-lived reversal of the ptosis or weakness clinches the diagnosis.
Step 3: Supporting investigations include antibodies to the acetylcholine receptor, which are almost diagnostic when present but can be negative in true disease, and slow repetitive nerve stimulation, which reveals a falling response amplitude.
Step 4: Creatine kinase and a muscle biopsy are aimed at muscle-fibre disease rather than the junction, and a routine EMG lacks the specificity of the drug test, so none of these is the single most useful choice.
\[\boxed{\text{Edrophonium test}}\]
Step 2: To confirm it quickly, the edrophonium challenge is preferred. By briefly blocking acetylcholinesterase, edrophonium boosts available acetylcholine, and an immediate but short-lived reversal of the ptosis or weakness clinches the diagnosis.
Step 3: Supporting investigations include antibodies to the acetylcholine receptor, which are almost diagnostic when present but can be negative in true disease, and slow repetitive nerve stimulation, which reveals a falling response amplitude.
Step 4: Creatine kinase and a muscle biopsy are aimed at muscle-fibre disease rather than the junction, and a routine EMG lacks the specificity of the drug test, so none of these is the single most useful choice.
\[\boxed{\text{Edrophonium test}}\]
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