USMLE Prep - Medical Reference Library

Myasthenic Crisis — Airway Strategy, IVIG vs PLEX, and Weaning

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

Synopsis:

Impending respiratory failure from myasthenia gravis requires ICU-level care; plan early airway strategy, treat with IVIG or plasma exchange, optimize anticholinesterase and immunotherapy, and prevent precipitants while using objective measures to guide extubation.

Key Points

  • Stabilize ABCs; treat life‑threatening derangements immediately.
  • Confirm diagnosis early with highest‑yield imaging/labs.
  • Initiate guideline‑based therapy and escalate by response.
  • Plan disposition and follow‑up explicitly.

Clinical Synopsis & Reasoning

Myasthenic crisis is impending/established ventilatory failure due to MG. Secure airway early; use short‑acting neuromuscular blockers if needed and avoid agents that worsen neuromuscular transmission. Choose IVIG 0.4 g/kg/day for 5 days or plasma exchange (5–6 exchanges), manage triggers, and titrate chronic immunotherapies. Extubation is guided by NIF, vital capacity, and clinical recovery.

Treatment Strategy & Disposition

Myasthenic crisis is impending/established ventilatory failure due to MG. Secure airway early; use short‑acting neuromuscular blockers if needed and avoid agents that worsen neuromuscular transmission. Choose IVIG 0.4 g/kg/day for 5 days or plasma exchange (5–6 exchanges), manage triggers, and titrate chronic immunotherapies. Extubation is guided by NIF, vital capacity, and clinical recovery.

Epidemiology / Risk Factors

  • Risk varies by comorbidity and precipitating factors

Initial Targets

ParameterTarget/Action
HemodynamicsMaintain perfusion; avoid hypotension
MonitoringSerial exam, labs, and imaging
TherapyStart early, reassess, de‑escalate when appropriate

Investigations

TestRole / RationaleTypical FindingsNotes
CBCScreen leukocytosis/anemiaContext‑specificTrend response
BMPElectrolytes/renal functionDerangements commonReplace K+/Mg2+
Key imagingCondition‑specific (CTA/MRI/Endoscopy)See textDo not delay when red flags

Pharmacology

MedicationMechanismOnsetRole in TherapyLimitations
IVIG 0.4 g/kg/day ×5ImmunotherapyDaysFirst‑line with PLEXHeadache, thrombosis risk
Plasma exchange (5–6)ImmunotherapyDaysAlternative first‑lineAccess complications
Pyridostigmine (careful)AChE inhibitorMinutesSymptom controlSecretions/bradycardia

Prognosis / Complications

  • Outcome depends on timeliness of diagnosis and definitive therapy

Patient Education / Counseling

  • Explain red flags, adherence, and follow‑up plan

References

  1. International Consensus Guidance for MG (2021) — Link
  2. SOP Myasthenic Crisis (2019) — Link