A 28-year-old man with known generalized myasthenia gravis on pyridostigmine presents to the emergency department with acute onset of severe weakness, respiratory distress, and difficulty swallowing over the past 6 hours. Vital signs: RR 28/min, SpO₂ 88% on room air, BP 140/90 mmHg. There is no recent infection or medication change. What is the most appropriate immediate action?

Explanation

## Management of Myasthenic Crisis **Key Point:** Myasthenic crisis is a life-threatening emergency requiring immediate airway protection and immunotherapy (plasmapheresis or IVIG). The clinical presentation—acute respiratory failure in a known MG patient without recent medication changes—is diagnostic of myasthenic crisis, not cholinergic crisis. ### Recognition of Myasthenic Crisis The patient meets criteria for myasthenic crisis: - Known MG with acute decompensation - Respiratory compromise (RR 28, SpO₂ 88%) - Bulbar weakness (difficulty swallowing) - No recent infection or medication change (rules out cholinergic crisis from overdose) **High-Yield:** Myasthenic crisis occurs in 15–20% of MG patients and is characterized by: - Acute respiratory failure requiring mechanical ventilation - Triggered by infection, surgery, medication non-compliance, or pregnancy - Mortality 5–10% if untreated; <5% with modern ICU care ### Immediate Management Algorithm ```mermaid flowchart TD A[Acute respiratory failure in MG patient]:::outcome --> B{Airway patent?}:::decision B -->|No/Compromised| C[Intubate and mechanically ventilate]:::urgent B -->|Yes| D[Assess SpO2 and respiratory reserve]:::action C --> E[ICU admission]:::action D --> F{SpO2 < 92% or RR > 25?}:::decision F -->|Yes| G[Prepare for intubation]:::urgent F -->|No| H[Close monitoring]:::action E --> I[Initiate plasmapheresis or IVIG]:::action H --> I I --> J[Avoid pyridostigmine temporarily]:::action J --> K[Supportive care + immunotherapy]:::action ``` **Clinical Pearl:** In myasthenic crisis, pyridostigmine should be **held or reduced** because: - It may worsen respiratory secretions and increase aspiration risk - Plasmapheresis/IVIG address the underlying immune pathology - Symptomatic relief is secondary to survival ### Plasmapheresis vs. IVIG | Feature | Plasmapheresis | IVIG | |---|---|---| | **Mechanism** | Removes circulating AChR antibodies | Modulates B-cell and complement activation | | **Onset** | 24–48 hours | 3–5 days | | **Duration** | 2–4 weeks | 3–4 weeks | | **Advantage** | Faster response in critical patients | Easier access, no vascular access needed | | **Disadvantage** | Requires vascular access, apheresis center | Slower onset, hypervolemia risk | | **Choice in crisis** | Preferred if available and urgent | Alternative if plasmapheresis unavailable | **Warning:** Do NOT perform edrophonium (Tensilon) testing in a patient with respiratory compromise—it can precipitate severe bronchospasm and apnea. Edrophonium is also rarely used now due to availability issues. **Mnemonic: CRISIS** — **C**ritical airway assessment, **R**espiratory support (intubation if needed), **I**mmunotherapy (plasmapheresis/IVIG), **S**upport in ICU, **I**nfection screening, **S**ymptomatic agents held temporarily.