What is the treatment for myasthenia gravis?

Treatment of Myasthenia Gravis

The first-line treatment for myasthenia gravis is pyridostigmine, with addition of corticosteroids (prednisone 1-1.5 mg/kg daily) for patients with more than mild disease, and concurrent initiation of steroid-sparing agents to minimize steroid exposure. 1, 2

Diagnostic Confirmation

• Diagnosis should be confirmed with:
  • Electrodiagnostic studies (repetitive nerve stimulation and single-fiber EMG)
  • Antibody testing (AChR, MuSK, Lrp4)
  • Chest imaging to evaluate for thymoma
  • Specialized tests like ice pack test or edrophonium (Tensilon) test when needed 1

Treatment Algorithm

Step 1: Symptomatic Treatment

• Start with pyridostigmine (Mestinon):
  • Initial dose: 30 mg orally three times daily
  • Titrate gradually based on symptoms
  • Maximum dose: 120 mg four times daily (up to 600 mg daily in severe cases)
  • Note: 30 mg oral pyridostigmine corresponds to 1 mg IV or 0.75 mg neostigmine IM 1

Step 2: Immunosuppressive Therapy

For patients with more than mild disease or inadequate response to pyridostigmine:

• Corticosteroids:

  • Prednisone 0.5-1.5 mg/kg orally daily
  • Response rate: 66-85% of patients 1

• Steroid-sparing agents (start concurrently with corticosteroids):

  • Methotrexate: 15 mg weekly
  • Azathioprine: 2 mg/kg of ideal body weight in divided doses
  • Mycophenolate mofetil: 500 mg twice daily, increasing to 1000 mg twice daily 1, 3

Step 3: Management of Refractory Disease

For patients with inadequate response to standard immunosuppression:

• Rituximab 3
• IVIG or plasmapheresis 1, 3

Step 4: Thymectomy

• Indicated for all patients with thymoma
• Beneficial in AChR antibody-positive generalized MG patients up to age 65
• Can lead to remission rates of approximately 11.6% 1, 3

Crisis Management

For myasthenic crisis:

• Hospital admission with ICU monitoring
• Treatment options:
  • IVIG 2 g/kg over 5 days, or
  • Plasmapheresis for 5 days 1

Monitoring

• Regular neurological assessments
• Pulmonary function tests:
  • Negative inspiratory force (NIF)
  • Vital capacity (VC)
• NIF interpretation:

  • -60 cm H2O: Continue routine monitoring

  • -20 to -60 cm H2O: Close monitoring and potential intervention 1

Important Medication Considerations

Medications to Avoid

• β-blockers
• IV magnesium
• Fluoroquinolones
• Aminoglycosides
• Macrolides 1

Anesthesia Considerations

• Safe anesthetic agents:

  • Propofol, Sevoflurane, isoflurane
  • Fentanyl, remifentanil
  • Lidocaine, bupivacaine
  • Rocuronium (preferred as it can be antagonized with sugammadex)

• Avoid:

  • Atracurium
  • Mivacurium
  • Succinylcholine 1

Special Populations

Ocular MG

• Pyridostigmine for symptomatic control
• Early treatment with corticosteroids when ocular motility is abnormal and fails to respond to symptomatic treatment 3

Elderly Patients

• Consider comorbidities when selecting immunosuppressive agents
• May require dose adjustments based on renal and hepatic function 3

Women of Childbearing Age

• Consider potential teratogenicity of immunosuppressive agents
• Consult with specialists regarding medication safety during pregnancy 3

Common Pitfalls and Caveats

• Undertreatment: Aiming for complete remission or minimal manifestations should be the goal, not just symptom improvement
• Delayed initiation of steroid-sparing agents: These should be started concurrently with corticosteroids to minimize steroid exposure
• Failure to recognize and manage fatigue separately from fatigable weakness
• Overlooking respiratory function monitoring, which is critical for early detection of crisis
• Not addressing dysfunctional breathing patterns that may require specific respiratory physiotherapy techniques 1, 3