What is the initial treatment for myasthenia gravis?

Initial Treatment for Myasthenia Gravis

The initial treatment for myasthenia gravis should be pyridostigmine, starting at 30 mg orally three times a day and gradually increasing to a maximum of 120 mg orally four times a day as tolerated and based on symptoms. 1, 2

Diagnostic Workup Before Treatment

Before initiating treatment, a thorough diagnostic workup should be performed:

• Check acetylcholine receptor (AChR) and antistriated muscle antibodies; if AChR antibodies are negative, consider muscle-specific kinase and lipoprotein-related 4 antibodies 1
• Assess pulmonary function with negative inspiratory force and vital capacity measurements 1
• Test for possible concurrent myositis with CPK, aldolase, ESR, and CRP 1
• Consider MRI of brain and/or spine depending on symptoms to rule out CNS involvement 1
• If respiratory insufficiency or elevated CPK/troponin T is present, perform cardiac examination with ECG and echocardiogram to evaluate for possible concomitant myocarditis 1
• Obtain neurology consultation 1
• Conduct electrodiagnostic studies, including neuromuscular junction testing with repetitive stimulation and/or jitter studies 1

Treatment Algorithm Based on Disease Severity

Mild Disease (Grade 2 - Some symptoms interfering with ADLs)

• Start with pyridostigmine 30 mg orally three times daily, gradually increasing to maximum of 120 mg orally four times daily as tolerated 1, 3
• If symptoms persist despite pyridostigmine, add corticosteroids (prednisone 1-1.5 mg/kg orally daily) 1
• Wean medications based on symptom improvement 1

Moderate to Severe Disease (Grade 3-4 - Limiting self-care, respiratory involvement)

• Admit patient, may need ICU-level monitoring 1
• Initiate corticosteroids immediately 1
• Add IVIG 2 g/kg over 5 days (0.4 g/kg/day) or plasmapheresis for 5 days 1
• Provide frequent pulmonary function assessment 1
• Conduct daily neurologic evaluation 1

Important Considerations

• Avoid medications that can worsen myasthenia gravis: β-blockers, IV magnesium, fluoroquinolones, aminoglycosides, and macrolides 1, 4
• Pyridostigmine provides only partial benefit in many patients, with approximately 50% of patients showing minimal response, particularly those with ocular myasthenia 1, 5
• Most patients eventually require long-term immunosuppressive therapies, most frequently corticosteroids and/or azathioprine 3, 5
• Side effects of pyridostigmine are common (reported in up to 91% of patients) and include gastrointestinal symptoms (flatulence, diarrhea, abdominal cramps), urinary urgency, muscle cramps, blurred vision, and hyperhidrosis 6

Long-term Management Options

• For patients not responding adequately to initial therapy, consider:
  • Azathioprine, cyclosporine, mycophenolate mofetil, or other immunosuppressants 7, 5
  • Thymectomy, particularly in AChR antibody-positive generalized MG patients under 65 years 5
  • Rituximab for refractory cases 5

Monitoring and Follow-up

• Regular assessment of symptom control and medication side effects 6
• Frequent pulmonary function testing in patients with moderate to severe disease 1
• Vigilance for potential development of myasthenic crisis requiring intensive care 1