PLEX for Impending Myasthenia Gravis Crisis
Yes, therapeutic plasma exchange (PLEX) is absolutely appropriate and strongly recommended for adult patients with impending myasthenia gravis crisis, particularly for Grade 3-4 toxicity (severe weakness, dysphagia, facial weakness, respiratory muscle weakness, or rapidly progressive symptoms). 1
When to Use PLEX
For impending or manifest myasthenic crisis, PLEX should be initiated immediately alongside corticosteroids in patients with:
- Grade 3-4 severity (limiting self-care, weakness limiting walking, ANY dysphagia, facial weakness, respiratory muscle weakness, or rapidly progressive symptoms) 2
- MGFA severity class III-V (moderate to severe generalized weakness to myasthenic crisis) 2
- Respiratory insufficiency requiring monitoring 1
The key distinction is that all grades of myasthenia gravis warrant work-up and intervention given the potential for progressive disease to lead to respiratory compromise 1. There is no Grade 1 toxicity in myasthenia gravis—by definition, symptomatic disease requires intervention.
PLEX vs IVIG: The Evidence
PLEX and IVIG have comparable efficacy 3. A Class I randomized controlled trial demonstrated that both treatments reduced disease severity scores equally, with 69% improvement on IVIG and 65% on PLEX, with similar duration of effect 3. The choice between them should be based on:
- Availability and access - PLEX requires specialized equipment and trained personnel
- Cost considerations - PLEX is generally less expensive (
$4,500-5,000) than IVIG ($12,000-16,000) 4 - Patient factors - PLEX requires adequate vascular access and hemodynamic stability
- Speed of response - Both work rapidly, but PLEX may have a slight edge in reducing duration of mechanical ventilation 5
Specific PLEX Protocol
For Grade 3-4 impending/manifest crisis:
- PLEX: 5 sessions over 5 days (typically 1.0-1.5 plasma volume exchanges per session, approximately 200-250 mL/kg) 1
- Concurrent corticosteroids: Continue methylprednisolone 2-4 mg/kg/day 1
- Alternative: IVIG 2 g/kg IV over 5 days (0.4 g/kg/day) 1, 2
Predictors of Good Response to PLEX
Recent evidence identifies specific factors predicting better response to PLEX:
- Presence of thymoma (100% response vs 50% without, P=0.002) 6
- High concentration of AChR antibodies (37.37 nmol/L vs 25.4 nmol/L in responders, P=0.039) 6
- Respiratory symptoms show the most remarkable improvement (72% response rate) 6
- Extraocular symptoms are least sensitive (only 8% response) 6
Critical Management Algorithm
Step 1: Immediate Assessment
- Pulmonary function testing with negative inspiratory force (NIF) and vital capacity (VC) 1
- AChR antibodies, anti-striated muscle antibodies 1
- CPK, troponin, ECG, echocardiogram to rule out concurrent myocarditis 1
- Neurology consultation 1
Step 2: Admit to ICU-capable unit 1, 2
Step 3: Initiate Treatment
- Permanently discontinue immune checkpoint inhibitors if applicable 1
- Start PLEX (5 sessions) OR IVIG (2 g/kg over 5 days) 1, 2
- Continue corticosteroids 1, 2
- Pyridostigmine (30 mg PO TID, titrate to max 120 mg QID) 1
Step 4: Monitoring
Critical Pitfalls to Avoid
Medications that worsen myasthenia gravis must be stopped immediately:
Do not delay treatment waiting for antibody results - the turnaround time can be several days, and treatment must be started immediately when crisis is suspected 7.
Avoid sequential PLEX after IVIG - plasmapheresis immediately after IVIG will remove the administered immunoglobulin 2.
Novel Considerations
Emerging evidence suggests nanomembrane-based TPE technology may reduce the need for invasive mechanical ventilation (42% vs 83% with conventional treatment, P=0.02) 5. TPE and non-invasive ventilation (NIV) were independent predictors for short-term (≤7 days) respiratory support 5.
Consider rituximab if refractory to IVIG or plasmapheresis 2.