Guillain-Barre syndrome vs Myasthenia gravis
How to tell Guillain-Barre syndrome and Myasthenia gravis apart when a board question makes them look alike.
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Absent deep tendon reflexes in progressive generalized weakness points to Guillain-Barre syndrome rather than myasthenia gravis.
Side by side
Rapidly progressive ascending weakness with areflexia after recent infection supports Guillain-Barre syndrome.
Fluctuating fatigable weakness, often ocular or bulbar first, with preserved reflexes suggests myasthenia gravis.
Immune-mediated demyelination of peripheral nerves causes conduction slowing and autonomic instability.
Autoantibodies against postsynaptic acetylcholine receptors reduce neuromuscular transmission during repeated use.
CSF after the first week often shows albuminocytologic dissociation with protein above 45 mg/dL and fewer than 10 WBC/uL, and nerve studies show demyelinating slowing.
Acetylcholine receptor antibodies and decrement greater than 10% on low-frequency repetitive nerve stimulation support myasthenia gravis; CSF is usually normal.
The trap
The dangerous error is treating progressive areflexic weakness as myasthenia and sending home. Reflex loss plus autonomic or respiratory decline requires monitored admission for impending neuromuscular respiratory failure.
The repair move
Next best step: admit for continuous respiratory and autonomic monitoring, check serial FVC and inspiratory force every 4 to 6 hours, and start IVIG 0.4 g/kg/day for 5 days or plasmapheresis. Prepare early intubation when FVC drops below about 15 to 20 mL/kg or inspiratory force weakens toward minus 30 cm H2O.
Try a free question
CoreA 40-year-old man develops ascending leg weakness and areflexia 10 days after gastroenteritis. FVC is 18 mL/kg. What is the next best step in management?
Show answer and explanation
Answer: C. Admit for respiratory monitoring and begin IVIG. Progressive areflexic weakness with declining FVC indicates Guillain-Barre syndrome requiring monitored admission and immunotherapy.
Why the other choices are tempting
- A. Wrong because outpatient care is unsafe with respiratory decline risk.
- B. Wrong because pyridostigmine treats myasthenia symptoms and does not address Guillain-Barre demyelination.
- D. Wrong because steroids alone are not effective first-line therapy for Guillain-Barre syndrome.
- E. Wrong because delaying treatment for nonurgent labs risks deterioration.
Flashcards
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Which examination finding best separates Guillain-Barre syndrome from myasthenia gravis in generalized weakness?
Loss of deep tendon reflexes strongly favors Guillain-Barre syndrome.
What CSF profile supports Guillain-Barre syndrome after the first week?
Elevated CSF protein with low cell count, called albuminocytologic dissociation, supports Guillain-Barre syndrome.
Quick answers
What is the fastest way to tell Guillain-Barre syndrome from Myasthenia gravis?
Absent deep tendon reflexes in progressive generalized weakness points to Guillain-Barre syndrome rather than myasthenia gravis.
What is the key clue for Guillain-Barre syndrome?
Rapidly progressive ascending weakness with areflexia after recent infection supports Guillain-Barre syndrome.
What is the key clue for Myasthenia gravis?
Fluctuating fatigable weakness, often ocular or bulbar first, with preserved reflexes suggests myasthenia gravis.
What is the common trap with Guillain-Barre syndrome vs Myasthenia gravis?
The dangerous error is treating progressive areflexic weakness as myasthenia and sending home. Reflex loss plus autonomic or respiratory decline requires monitored admission for impending neuromuscular respiratory failure.