Myasthenia gravis: The Daily PANCE Blueprint
A 34-year-old woman presents with a 6-week history of intermittent double vision and drooping of both eyelids. She notes her symptoms are mild when she wakes but worsen steadily as the day goes on, particularly while reading or watching television in the evening, and they ease after she rests or naps. She denies eye pain, headache, or any change in the size of her pupils. She has no limb weakness, numbness, or bowel/bladder symptoms. Her past medical history is unremarkable and she takes no medications. Vital signs are normal, and her general neurologic screen shows normal strength, sensation, and reflexes. Which finding is most likely on physical examination?
A. Worsening ptosis with sustained upward gaze for 1–2 minutes
B. A fixed, dilated pupil that reacts poorly to light
C. A resting, pill-rolling tremor of the hand
D. Hyperreflexia with an extensor (upgoing) plantar response
E. Symmetric stocking-glove distribution sensory loss
Answer and topic summary
Myasthenia gravis is an autoimmune disorder of the postsynaptic acetylcholine receptors at the neuromuscular junction, and its hallmark is fatigable, fluctuating weakness that worsens with use and toward the end of the day and improves with rest — exactly the diurnal pattern this patient describes. More than half of patients present with purely ocular symptoms (ptosis and binocular diplopia). The classic bedside maneuver is to have the patient hold a sustained upgaze for 1–2 minutes, which fatigues the levator palpebrae and produces progressive ptosis; a positive ice-pack test (≥2 mm improvement in lid opening, sensitivity ~90%, specificity ~100%) supports the diagnosis. A defining feature is that the pupils are always spared in MG. Confirmation is with anti-acetylcholine-receptor antibodies first, then anti-MuSK/anti-LRP4 if seronegative, plus chest CT to evaluate for thymoma.
Why the Others Are Wrong:
- B. A fixed, dilated, poorly reactive (“blown”) pupil indicates CN III compression (e.g., posterior communicating artery aneurysm or uncal herniation) — a can’t-miss emergency; MG never involves the pupil.
- C. A resting pill-rolling tremor points to Parkinson disease, a basal-ganglia movement disorder, not a neuromuscular-junction problem, and does not fluctuate with fatigue.
- D. Hyperreflexia with a Babinski sign is an upper-motor-neuron (central) finding; MG is a neuromuscular-junction disorder with normal reflexes and no long-tract signs.
- E. Stocking-glove sensory loss reflects a peripheral polyneuropathy; MG is purely motor and causes no sensory deficits.
Top Pearl: Pupil-sparing, fatigable ptosis plus diplopia that worsen through the day = myasthenia gravis. If the pupil is blown, abandon MG and think CN III compression (aneurysm) instead.
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