Management of Myasthenia Gravis Crisis

Initial Assessment and Treatment

• The management of myasthenia gravis crisis requires immediate hospitalization with ICU-level monitoring, administration of corticosteroids, and initiation of either intravenous immunoglobulin (IVIG) or plasmapheresis to rapidly reduce antibody levels 1, 2, 3
• Perform immediate pulmonary function assessment with negative inspiratory force (NIF) and vital capacity (VC) measurements 1, 2
• Administer high-dose corticosteroids: methylprednisolone 1-2 mg/kg/day IV or prednisone 1-1.5 mg/kg/day orally 2, 4
• Start plasmapheresis (5 sessions over 5 days) OR IVIG (2 g/kg total dose over 5 days at 0.4 g/kg/day) 1, 2, 3

Diagnostic Workup

• Check acetylcholine receptor (AChR) antibodies and anti-striated muscle antibodies 1, 2, 3
• If AChR antibodies are negative, test for muscle-specific kinase (MuSK) and lipoprotein-related protein 4 (LRP4) antibodies 1, 2
• Measure CPK, aldolase, ESR, and CRP to evaluate for concurrent myositis 1, 3
• Perform cardiac evaluation with ECG and transthoracic echocardiogram if respiratory insufficiency or elevated CPK/troponin T to rule out concurrent myocarditis 1, 2

Medication Precautions

• IMMEDIATELY discontinue medications that can worsen myasthenia gravis: beta-blockers 1, IV magnesium (absolutely contraindicated) 5, fluoroquinolones 1, aminoglycosides 1, and macrolide antibiotics 1, 2, 5

Monitoring and Follow-up

• Daily neurological evaluation 2, 4
• Frequent assessment of respiratory function 1, 2
• Monitor for complications of immunotherapy 2
• Begin steroid taper 3-4 weeks after initiation, based on symptom improvement 1

Special Considerations

• ICPi-associated myasthenia gravis may be monophasic, potentially requiring less prolonged immunosuppression 2, 4
• If severe hypomagnesemia requires treatment, neurology consultation is mandatory before administration 5

Role of Negative Inspiratory Force (NIF) and Vital Capacity (VC) in Managing Myasthenia Gravis

Importance in Clinical Assessment

• NIF and VC measurements serve as critical components of the pulmonary function assessment in myasthenia gravis patients, especially when evaluating for respiratory compromise 6, 7
• These measurements should be performed as part of the initial diagnostic workup for all grades of myasthenia gravis, as respiratory muscle weakness represents the most severe manifestation of the disease 7

Clinical Decision Making

• The "20/30/40 rule" is used to identify patients at risk of respiratory failure: vital capacity <20 ml/kg, maximum inspiratory pressure <30 cmH₂O, or maximum expiratory pressure <40 cmH₂O 8
• Frequent pulmonary function assessment with NIF and VC is recommended for patients with moderate to severe generalized weakness (MGFA class III-V) 6
• Regular monitoring of respiratory function is advised even when patients don't show clinical signs of dyspnea, as respiratory insufficiency may develop without obvious symptoms 8

Management Implications

• For patients with moderate to severe myasthenia gravis (MGFA class III-V) with respiratory muscle weakness, frequent pulmonary function assessment including NIF and VC should be performed 6
• Treatment options for respiratory compromise include high-dose corticosteroids, IVIG (2 g/kg over 5 days), or plasmapheresis (5 sessions over 5 days) 7

Practical Application

• NIF and VC should be measured at baseline in all myasthenia gravis patients and monitored regularly during follow-up visits 7

Special Considerations

• Medications that can worsen myasthenia gravis (beta-blockers, IV magnesium, fluoroquinolones, aminoglycosides, and macrolides) should be avoided, as they may precipitate respiratory failure 7

Respiratory Status Testing in Myasthenia Gravis

Core Assessment Parameters

• The American College of Physicians, as reflected in MMWR Recommendations and Reports, suggests applying the "20/30/40 rule" to identify patients at risk of respiratory failure: vital capacity <20 ml/kg, maximum inspiratory pressure <30 cmH₂O, or maximum expiratory pressure <40 cmH₂O, and perform sniff nasal inspiratory pressure testing to evaluate diaphragm strength and inspiratory muscle function 9
• The single breath count test, which involves taking a deep breath and counting at a rate of two numbers per second while exhaling, can be used to assess respiratory muscle function, with counting to ≥25 correlating with normal respiratory muscle function 9

Monitoring Frequency and Approach

• The American Thoracic Society, as reflected in Chest, recommends conducting respiratory function assessments every 6 months in patients with stable disease 10
• The American Thoracic Society, as reflected in Chest, suggests considering polysomnography when there is concern that pulmonary function tests and clinical evaluation are not capturing complications such as hypoventilation 10

Special Considerations

• The Centers for Disease Control and Prevention, as reflected in MMWR Recommendations and Reports, notes that end-tidal carbon dioxide (EtCO2) monitoring is an optional modality for monitoring early respiratory failure, and pulse oximetry and arterial blood gases might not be reliable early indicators of emerging respiratory failure 9
• The American College of Chest Physicians, as reflected in Chest, recommends ensuring testing is performed by adequately trained practitioners familiar with assessing individuals with neuromuscular disorders 10

Treatment of Myasthenia Gravis Crisis

Medication Management

• The American Academy of Neurology recommends discontinue or withhold pyridostigmine in intubated patients, and for non-intubated patients with myasthenic symptoms, pyridostigmine may be used starting from 30 mg orally up to 600 mg daily 11
• The American Academy of Neurology suggests that in IV application, 30 mg oral pyridostigmine corresponds to 1 mg IV or 0.75 mg neostigmine IM 11

Monitoring and Care

• The British Journal of Anaesthesia recommends monitoring for a minimum of 24 hours in ICU, HDU, or recovery unit even after apparent stabilization 12

Plasma Exchange Regimen in Myasthenic Crisis

Standard Treatment Protocol

• The American Journal of Kidney Diseases recommends an alternative extended regimen of 7 exchanges over 14 days for severe cases 13, 14

Critical Medication Management During Treatment

• When using cyclophosphamide, the American Journal of Kidney Diseases suggests administering the infusion after the plasma exchange session 13, 14
• When using rituximab, the American Journal of Kidney Diseases advises holding plasma exchange for 48-72 hours after rituximab infusion to prevent antibody removal 13, 14

Safety Considerations

• The American Journal of Kidney Diseases states that plasma exchange carries risks including hemodynamic shifts, coagulation disorders, electrolyte imbalances, and line-related bacteremia, requiring careful monitoring and expertise in apheresis procedures 13, 14
• The American Journal of Kidney Diseases notes that plasma exchange requires specialized equipment and expertise, often necessitating transfer to tertiary academic centers 13, 14