Question

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. CPK
• B. Edrophonium test
• C. EMG
• D. Muscle biopsy

Hint:

A rapid-acting anticholinesterase that briefly reverses the ptosis points to the diagnosis.

Answer 1

The Correct Option is B

Step 1: The combination of fluctuating ptosis, restricted eye movements in all directions, proximal weakness, and fatigability that worsens with use is classic for myasthenia gravis, a disorder of the neuromuscular junction caused by antibodies against acetylcholine receptors.

Step 2: The edrophonium (Tensilon) test is the most useful bedside test here. Edrophonium is a short-acting acetylcholinesterase inhibitor that increases acetylcholine at the junction. A rapid, transient improvement in ptosis or weakness confirms the diagnosis, and the quick onset and short duration make it practical.

Step 3: Other confirmatory tests exist but are not the best single answer. Acetylcholine receptor antibodies are highly specific, yet a negative result does not exclude the disease. Repetitive nerve stimulation shows a decremental response of more than 10 to 15 percent in evoked amplitude.

Step 4: CPK and muscle biopsy assess primary muscle (myopathic) disease, and standard EMG is less specific for junction pathology than the edrophonium test, so they are not the most useful first test here.