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Acute neuromuscular weakness: Guillain–Barré syndrome and myasthenic crisis
In acute neuromuscular weakness the immediate danger is respiratory failure; measure vital capacity (FVC) and inspiratory and expiratory pressures, intubate before collapse, and treat with IVIG or plasma exchange in both Guillain–Barré syndrome and myasthenic crisis.
Why it matters in the exam
The classic question describes a patient with ascending leg weakness and lost reflexes a few weeks after diarrhoea or a respiratory infection — Guillain–Barré — or a myasthenic patient with ptosis, difficulty swallowing and breathlessness that worsened after an infection or a new drug. The correct step is measuring FVC and not oxygen saturation, because hypoxaemia appears late.
The "20-30-40" rule helps decide on intubation: FVC below 20 mL/kg, maximal inspiratory pressure weaker than 30 cm water, or maximal expiratory pressure below 40 cm water. Further signs for intubation: neck muscle weakness, inability to swallow secretions and a weak cough. In Guillain–Barré there is also autonomic instability — arrhythmias and swings in blood pressure — so the heart is monitored.
Treatment of Guillain–Barré is IVIG (0.4 g/kg per day for 5 days) or plasma exchange; steroids are not effective. Lumbar puncture shows high protein with few cells. In myasthenic crisis give IVIG or plasma exchange, stop aggravating drugs (aminoglycosides, fluoroquinolones, magnesium, beta-blockers) and treat infection. The differential includes spinal cord compression, hypokalaemic periodic paralysis and tick paralysis.
Key points
- The immediate danger — respiratory failure; measure FVC.
- The 20-30-40 rule for deciding on intubation.
- Guillain–Barré: ascending weakness, areflexia, high CSF protein — IVIG or plasma exchange.
- Myasthenic crisis: IVIG or plasma exchange and stop aggravating drugs.
- Exclude cord compression and periodic paralysis.
Summary table
| Condition | Picture | Test | Treatment |
|---|---|---|---|
| Guillain–Barré | Symmetric ascending weakness, areflexia, after infection | Lumbar puncture: high protein, few cells; nerve conduction | IVIG or plasma exchange; no steroids |
| Myasthenic crisis | Ptosis, diplopia, dysphagia, respiratory weakness worse with effort | FVC, antibodies | IVIG or plasma exchange, stop aggravating drugs |
| Spinal cord compression | Leg weakness, sensory level, sphincter problems | Urgent MRI | Steroids for tumour, surgery |
| Periodic paralysis | Sudden weakness, reduced reflexes, low potassium | Potassium, thyroid function | Careful potassium correction |
| Impending respiratory failure | FVC below 20 mL/kg, weak cough | Repeat FVC | Early intubation |
A free exam question
בת 43 , ברקע אסתמה וסוכרת סוג 2 . פנתה למלר"ד בשל קוצר נשימה חריף. סימנים חיוניים: דופק 130 , ל"ד 150/90 , סטורציה 88% ,באוויר חדר 32 נשימות בדקה. גלוקוז 320 מ"ג/ד"ל . טופלה בסטרואידים, מגנזיום ואינהלציות תכופות של Salbutamol ואינסולין . סימנים חיוניים כעבור 3 שעות: סטורציה 96% ,באוויר חדר 18 נשימות לדקה, גלוקוז 110 מ"ג/ד"ל. כעת מתלוננת על חולשה פרוקסימלית חדשה וסימטרית ועל רעד עדין בידיים. בבדיקתה: חולשה סימטרית בכתפיים ובירכיים, רפלקסים שמורים, ללא חסר נוירולוגי פוקלי. מה מהבאים י כול להסביר את התלונות החדשות? (the question as examined, in Hebrew)
- א. ירידה חדה ומהירה ברמות הגלוקוז
- ב. CTA .של הראש והצוואר
- ג. ניקור מותני ) LP
- ד. בדיקת אלקטרוליטים בדם
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Sources
- Leonhard SE et al., Diagnosis and management of Guillain–Barré syndrome in ten steps (Nature Reviews Neurology), 2019 — Treatment and respiratory monitoring
- International consensus guidance for management of myasthenia gravis, 2020 update — Myasthenic crisis
- Tintinalli's Emergency Medicine: A Comprehensive Study Guide, 9th edition (2020) — Acute peripheral neurologic disorders
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.