USMLE Prep - Medical Reference Library

Myasthenic Crisis — Respiratory and Immunotherapy

System: Neurology • Reviewed: Aug 31, 2025 • Step 1Step 2Step 3

Synopsis:

Impending or established respiratory failure from myasthenia gravis requires ICU admission, ventilatory support, and early IVIG or plasma exchange.

Key Points

  • Stabilize ABCs; begin targeted evaluation without delaying life-saving therapy.
  • Use system-specific risk tools to guide testing and disposition.
  • Order high-yield tests first; escalate imaging when indicated.
  • Start evidence-based initial therapy and reassess frequently.

Algorithm

  1. Primary survey and vitals; IV access and monitors.
  2. Focused history/physical; identify red flags and likely etiologies.
  3. Order system-appropriate labs and imaging (see Investigations).
  4. Initiate guideline-based empiric therapy (see Pharmacology).
  5. Reassess response; arrange consultation and definitive management.

Clinical Synopsis & Reasoning

For Myasthenic Crisis Respiratory Immunotherapy, frame the differential by acuity and pathophysiology, then align diagnostics to the leading hypotheses. Prioritize stabilization while obtaining high‑yield studies such as CT Head (NC) (Hemorrhage exclusion), Glucose (POC) (Exclude hypoglycemia), MRI Brain (selected) (Ischemia/structural). Incorporate bedside imaging and targeted labs to define severity and identify complications; synthesize results with clinical trajectory to refine the working diagnosis and disposition needs.


Treatment Strategy & Disposition

Initiate disease‑directed therapy alongside supportive care, titrating to objective response. Pharmacologic options commonly include Thrombolytic (eligible), Antiepileptics. Use validated frameworks (e.g., Intubation Thresholds (Typical)) to guide escalation and site of care. Address precipitating factors, de‑escalate empiric therapies with data, and arrange follow‑up for monitoring and risk‑factor modification; admit patients with instability, high risk of deterioration, or needs for close monitoring.


Epidemiology / Risk Factors

  • Hypertension, AF, atherosclerosis; prior stroke/TIA

Investigations

TestRole / RationaleTypical FindingsNotes
CT Head (NC)Hemorrhage exclusionAcute bloodFirst-line
Glucose (POC)Exclude hypoglycemiaLowTreat promptly
MRI Brain (selected)Ischemia/structuralDiffusion restriction

Intubation Thresholds (Typical)

TestConcerning values
Vital capacity<15 to 20 mL kg
Negative inspiratory forceWeaker than −20 cm H2O
Rapid declineTrend matters even if above cutoffs

Pharmacology

MedicationMechanismOnsetRole in TherapyLimitations
IVIG or plasmapheresisImmune modulationDaysRapid improvementInfusion reactions
Pyridostigmine (maintenance)AChE inhibitionHoursSymptom control (not in crisis)Cholinergic effects

Prognosis / Complications

  • Outcome tied to time-to-reperfusion; aspiration/DVT risks

Patient Education / Counseling

  • Explain red flags and when to seek emergent care.
  • Reinforce medication adherence and follow-up plan.

Notes

Screen for myasthenic vs cholinergic crisis. Coordinate with neurology for long term immunomodulation after stabilization.


References

  1. Myasthenia Gravis Foundation Resources — Link
  2. Neurocritical Care Society — NMJ Disorders — Link